France



5d metals are used in electronic architectures because of their high spin-orbit coupling (SOC) leading to efficient spin ↔ electric conversion and strong magnetic interactions. When C&lt;sub&gt;60&lt;/sub&gt; is grown on a metal, the electronic structure is altered due to hybridisation and charge transfer. Previously, it has been shown that this can lead to the emergence of spin ordering [1]. This interfacial effect is also critical in spin filtering and spin transport effects [2]. We have studied the spin Hall magnetoresistance (SHMR) for YIG/Pt/C&lt;sub&gt;60&lt;/sub&gt; and YIG/Ta/C&lt;sub&gt;60.&lt;/sub&gt; [3]. The SHMR at room temperature are up to a factor 6 higher than for the pristine metals, with the spin Hall angle increased by 20-60%. Here we studied YIG/PtMn with without C&lt;sub&gt;60&lt;/sub&gt;. PtMn is an antiferromagnet that has been shown to have a strong spin Hall effect [4]. This will allow us to determine if the molecular orientation can play a role in the enhanced SOC observed in Pt. We aim to: investigate the mechanisms that generate spin orbit scattering at the hybrid conducting interface and maximise the effect.&lt;br/&gt;By fitting the SHMR data, we can extract the spin Hall angle which is significantly higher with the molecular overlayer. The SHMR saturates once the applied field saturates the magnetisation out-of-plane, at 0.1-0.15 T for a YIG film, and no higher than 0.5 T for any measured condition. However, above this field range, other contributions such as Koehler MR, localisation and the Hanle effect can result in significant linear contributions to the MR that would artificially enhance the SHMR ratio and spin hall angle [Fig1]. Thus, the spin Hall angle ΘSH is bigger for PtMn/C60 than PtMn, which we attribute to an enhancement of the spin orbit coupling (SOC) by the C&lt;sub&gt;60&lt;/sub&gt;. Figure 2 shows the maximum SHMR measured as a function of the PtMn thickness for both pure metal and PtMn covered on molecules. Also, the PtMn/C&lt;sub&gt;60 &lt;/sub&gt;SHMR value is increased after annealing the sample at 200 C.

**References:**

References:&lt;br/&gt;1. F. Al ma’mari, &lt;i&gt;et al&lt;/i&gt;., Nature. 524, 69—73 (2015)&lt;br/&gt;2. M. Cinchetti, &lt;i&gt;et al&lt;/i&gt;., Nature materials. 16, 507 (2017)&lt;br/&gt;3. S. Alotibi, et al., arXiv preprint: 1912. 02712, 2020.&lt;br/&gt;4. Y. Ou, Phys. Rev. B 93, 220405(R) (2016).

**Images:**

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INTERMAG 2021

 Effects of a Molecular C60 Interfaces on the Spin Hall Magnetoresistance of YIG/PtMn

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5d metals are used in electronic architectures because of their high spin-orbit coupling (SOC) leading to efficient spin ↔ electric conversion and strong magnetic interactions. When C60 is grown on a metal, the electronic structure is altered due to hybridisation and charge transfer. Previously, it has been shown that this can lead to the emergence of spin ordering [1]. This interfacial effect is also critical in spin filtering and spin transport effects [2]. We have studied the spin Hall magnetoresistance (SHMR) for YIG/Pt/C60 and YIG/Ta/C60. [3]. The SHMR at room temperature are up to a factor 6 higher than for the pristine metals, with the spin Hall angle increased by 20-60%. Here we studied YIG/PtMn with without C60. PtMn is an antiferromagnet that has been shown to have a strong spin Hall effect [4]. This will allow us to determine if the molecular orientation can play a role in the enhanced SOC observed in Pt. We aim to: investigate the mechanisms that generate spin orbit scattering at the hybrid conducting interface and maximise the effect. By fitting the SHMR data, we can extract the spin Hall angle which is significantly higher with the molecular overlayer. The SHMR saturates once the applied field saturates the magnetisation out-of-plane, at 0.1-0.15 T for a YIG film, and no higher than 0.5 T for any measured condition. However, above this field range, other contributions such as Koehler MR, localisation and the Hanle effect can result in significant linear contributions to the MR that would artificially enhance the SHMR ratio and spin hall angle [Fig1]. Thus, the spin Hall angle ΘSH is bigger for PtMn/C60 than PtMn, which we attribute to an enhancement of the spin orbit coupling (SOC) by the C60. Figure 2 shows the maximum SHMR measured as a function of the PtMn thickness for both pure metal and PtMn covered on molecules. Also, the PtMn/C60 SHMR value is increased after annealing the sample at 200 C.

**References:**

References: 1. F. Al ma’mari, et al., Nature. 524, 69—73 (2015) 2. M. Cinchetti, et al., Nature materials. 16, 507 (2017) 3. S. Alotibi, et al., arXiv preprint: 1912. 02712, 2020. 4. Y. Ou, Phys. Rev. B 93, 220405(R) (2016).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/081f905ccccdb5556742fbf743fdc34e.jpg)

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poster

In our information society, the importance of energy conservation is increasing year by year. To tackle this issue, the transition from volatile memory to non-volatile memory can be a solution. One of the candidates for non-volatile memories is a racetrack memory[1], driven by current-induced domain wall motion (CIDWM). For practical use, faster CIDWM and lower threshold current density are key factors. In order to reach this goal, we have been focusing on and investigating Mn4N as a promising material. Mn4N film is an antiperovskite ferrimagnet without rare-earth elements, which is advantageous in fast magnetization reversal due to its perpendicular magnetic anisotropy (Ku ~ 1.1×105 J/m3) and a small saturation magnetization (MS ~ 80 kA/m)[2]. Previous study on 1-2μm-wide Mn4N strips showed the fastest spin-transfer-torque-driven domain wall motion (vDW ~ 900 m/s at 1.3×1012 A/m2) at room temperature (RT)[2], comparable to those reported in the system including rare-earth 4f magnets or heavy metals. To achieve faster vDW, Mn4N based mixed crystals have been studied in pursuit of the use of magnetic and/or angular momentum compensation for more efficient CIDWM thanks to diverged damping constants. Recently, Mn4-xNixN films have been suggested to have a magnetic compensation (MC) point between x = 0.1 and 0.25 at RT[3]. We found that Mn4-xCoxN films have a compensation point between x = 0 and 0.8 from x-ray magnetic circular dichroism (XMCD) measurements[4]. However, there is a lack of information about the magnetic behavior of Mn4-xCoxN at values x much smaller or larger than 0.8. Considering that the compensation in Mn4-xNixN takes place in a small range of composition x, further compensation points can be found when x is far from 0.8. In this work, we performed XMCD measurements on Mn4-xCoxN epitaxial films at x = 0.2 and 1.3 and investigated the change in magnetic structures by composition ratio to verify MC at RT. 20-30 nm-thick Mn4-xCoxN films with x = 0-1.3 were epitaxially grown on SrTiO3(001) substrates by molecular beam epitaxy. SiO2 or Ta capping layers were sputtered in-situ on the surface to prevent oxidation. X-ray absorption spectroscopy (XAS) and XMCD measurements were performed at BL-16A of KEK-PF for x = 0.2 and 1.3. In these measurements, we applied an external magnetic field of 5 T perpendicular to sample surfaces. The incidence angle of the circularly polarized x-ray was 54.7°(magic angle) to the plane in order to simplify the sum rule calculation. For x = 0.8, the XMCD measurements were carried out at BL23SU of SPring-8[4]. Figures 1(a)-1(c) show the XAS and XMCD spectra of Mn in Mn4-xCoxN at x = 0.2, 0.8[4], and 1.3, respectively. In these figures, the sharp peak near 640 eV comes from Mn atoms at corner sites (I sites), and the broad peak near 643 eV originates from those at face-centered sites (II sites)[4]. We observed the sign reversals of XMCD signals between x = 0.2 and 0.8, and also between x = 0.8 and 1.3. Similar sign reversals were also observed in the XMCD signals of Co atoms. These results indicate that MC occurs twice in the range of x = 0-1.3 in Mn4-xCoxN. Besides, the XAS spectra of Co indicate that Co preferentially occupied the corner sites. We also calculated the mean magnetic moment of Co by using the sum rule analysis. Figure 2 shows the expected magnetic structures derived from the XMCD measurements. Around x = 0.2, Co atoms preferentially replaced Mn(I) and thus the total magnetic moment of I site and that of face-centered site (II site) became closer. With further increasing x, the total magnetic moment became zero. In this manner, the first MC occurred between x = 0.2 and 0.8. After the first MC, the total magnetic moment of II sites became larger and this led to the reversal of magnetic moments of all atoms in order to minimize the Zeeman energy. Above x = 0.8, Co atoms gradually got to occupy II sites and thus the second MC occurs. As far as we investigated, Mn4-xCoxN is the only material which has two MC points at RT. This property can be useful for spintronic devices, for example, the use of compensation in a wide range of composition. The XMCD experiment for x = 0.2 and 1.3 was performed with the approval of the Photon Factory Program Advisory Committee (Proposal No. 2019G574).

**References:**

[1] S. Parkin and S. Yang, Nat. Nanotechnol., Vol.10, p.195 (2015) [2] T. Gushi et al., Nano Lett., Vol.19, p.8716 (2019) [3] T. Komori et al., JAP, Vol.127, p.043903 (2020) [4] K. Ito et al., Phys. Rev. B, Vol.101, p104401 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/afcad013ae3441a446c71d093ae63afb.jpg)
Fig. 1 XAS (blue) and XMCD (black) spectra in (a) Mn3.8Co0.2N, (b) Mn3.2Co0.8N[3], and (c) Mn2.7Co1.3N films at the Mn L2,3 absorption edges.

![](https://assets.underline.io/uploads/markdown_image/1/image/3f59e17fa54814000208a461221f56c6.jpg)
Fig. 2 Schematic of the expected magnetic structures of Mn4-xCoxN.

 Two magnetic compensation compositions in Mn4-xCoxN epitaxial films at room temperature proved by X-ray magnetic circular dichroism

Single molecule magnetism (SMM) presents a novel avenue for the pursuit of a bottom up approach to the design of next generation magnets, their molecular origin of magnetism and sensitivity to their chemical environment allows SMMs to be designed and exploited at the molecular level1. Applications include proposals for SMMs to be used as qubits and components in spintronic devices2,3. Here we present the synthesis and magnetic properties of mononuclear Ln(III) complexes, where two Er(III) complexes exhibit SMM behavior and blocking temperatures of around 40K.4 We used a synthetic approach and ligand fine-tuning where the ligand field is favorable for the Er(III) compounds to exhibit SMM properties. Single crystal structure analysis was carried out to obtain structural information on all the presented complexes. The field dependence of the magnetization for both Er(III) compounds were measured at 2, 3 and 5 K; the magnetization curves did not saturate at high fields indicating the presence of significant magnetic anisotropy and/or low-lying excited states. In order to investigate the potential presence of slow relaxation of the magnetization caused by SMM behavior, ac magnetic susceptibility measurements were performed, in applied dc-fields from 0 to 3000 Oe, in attempts to suppress any quantum tunneling of the magnetization (QTM). For both compounds the in-phase and out-of-phase ac susceptibility show field-dependent signals; the optimum field was found to be 500 Oe and this was used for further ac measurements. In both cases, the ac measurements reveal temperature dependent in- and out-of-phase signals with clear maxima up to 3.5 K. The maxima of the frequency dependent out-of-phase susceptibility curves were used extract the relaxation time as a function of temperature.

**References:**

[1] B. M. Day, F.-S. Guo, R. A. Layfield, Acc. Chem. Res. 51,1880–1889 (2018). [2] M. Shiddiq et al., Nature 531, 348–351 (2016). [3] S. Thiele et al., Science 344, 1135–1138 (2014). [4] I.A. Kühne, et al., Dalton Trans 48, 15679 (2019)

**Images:**

 The Influence of Electron-Withdrawing Groups on the Relaxation Time of Field-Induced Er(III) Single Molecule Magnets.

Two-dimensional arrays of interacting magnetic nanostructures allow the exploration of the many body physics associated with highly frustrated magnets in a convenient manner. Based on a lab-on-chip approach, artificially made structures can be viewed as experimental simulators of frustrated magnetism, complementing what can be done with chemically synthesized compounds. For example, collective magnetic phenomena such as emergent charge crystallization, magnetic moment fragmentation, and Coulomb phase physics have been recently evidenced in artificial systems. If the initial motivation was to realize an artificial ice magnet, a wide range of systems have been now investigated, including structures that have no counterparts in bulk materials. Whether they are chemically synthesized or nanofabricated, the spin dynamics of frustrated magnets generally freezes before magnetic ordering eventually sets in at very low temperature. Here, we will show how dynamical freezing can be bypassed in an artificial kagome ice to access low-energy states [1]. More specifically, we will demonstrate that the a priori dynamically inaccessible ordered ground state and fragmented spin liquid configurations can be obtained reproducibly, imaged in real space at room temperature, and studied conveniently (Figs.1 and 2). We will then identify the mechanism by which dynamical freezing occurs in the dipolar kagome ice. Besides, although artificially made structures were initially designed to address the physics of frustrated spin models, they can be used to investigate vertex models as well. Experimental strategy to fabricate artificial vertex models will be also briefly discussed [2].

**References:**

[1] V. Schanilec et al., Phys. Rev. Lett. 125, 057203 (2020). [2] Y. Perrin et al., Phys. Rev. B 99, 224434 (2019).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/06cf2e370a40d127454b84c97e8d5755.jpg)
Real space magnetic images with their associated spin-charge representations in an artificial kagome ice trapped within a fragmented spin state. Scale bar is 6 μm.

![](https://assets.underline.io/uploads/markdown_image/1/image/c53af84486a627fed47bc581cd73f8c2.jpg)
Analysis of the pairwise spin correlations.

Dynamical freezing in an artificial kagome ice magnet

The realization of physical systems whose electronic and magnetic properties can be easily manipulated by playing with valence electrons are very promising from both the fundamental and applied perspectives. Half-metallic ferromagnets are ideal candidates for spintronic applications because of their high spin polarization of charge carriers at the Fermi level [1,2]. High Curie temperature is one of the important precondition of the half-metallic ferromagnets from the application point of view. Co2- based intermetallic Heusler alloys (L21 structure, space group Fm-3m, # 225) are among the most attractive half-metallic systems due to their high Curie temperatures, high spin polarization and the structural similarity to binary semiconductors [1,2]. The Co2FeSi (CFS) system is one such candidate of interest for spintronic applications due to its high Curie temperature crystallizing in the L21 structure but Fermi level falls on the edge of the minority conduction band (in both generalized gradient approximation (GGA) and GGA+U approach) making the system shy from being robust half metallic. High Tc = 1100K and large magnetic moment of 6.00 μB/f.u. is reported in Ref [3]. If one of the Co atom in CFS is replaced by low valence transition metal atom Y = Sc, Ti, V, Cr, Mn, and Fe, alloys with rich and useful properties can be tailored. The quaternary Heusler alloy CoFeMnSi [4] is observed theoretically and experimentally to be spin gapless semiconductor, CoFeCrSi [5] is reported to be half-metallic with some structural disorder, CoFeVSi and CoFeTiSi are reported theoretically to be nearly half-metallic and half-metallic respectively, but both are observed experimentally to show multi-phase behavior in bulk form. The Fermi level lies on the edge of the minority valence band in all Y substituted quaternary Heusler alloys, leading to an unstable half-metallicity. So, as we go from CFS to CoFeYSi, Fermi level is shifted from lower edge of conduction band to upper edge of valence band in minority spin channel which is in accordance to Ref. [2,6]. They have suggested that an expansion of the lattice should shift the Fermi level deeper in energy and the contraction should shift it higher in energy. Therefore, one can expect robust half metallicity with Fermi level exactly at the middle of the band gap for some intermediate Y concentrations in CFS due to the expansion of the lattice when Y with larger atomic radius substitutes for Co. The substitution of Y to Co may be also seen as d-electron deficiency. In this work, we have introduced the substitution of all low valence transition metal atoms Y = Sc, Ti, V, Cr, Mn, and Fe to Co atoms in the parent CFS system, and examined the structural, electronic, magnetic, and mechanical properties of quaternary Heusler compounds Co2-xYxFeSi (0≤x≤1) to get a global overview of the electronic, magnetic and mechanical properties, promising candidates for spintronics applications. All single phase alloys exhibit face centered cubic crystal structure with a strong tendency towards L21 ordering, as corroborated by X-ray diffraction. The low-temperature saturation magnetic moments agree fairly well with our theoretical results and also obey the Slater-Pauling rule, a prerequisite for half metallicity. Fig.1 shows the linear decrease of the spontaneous magnetizations measured at 2K with the valence electron counts per formula units with element Y = Ti, V, Cr, Mn, Fe, and Co in Co2-xYxFeSi (x = 0.50). All alloys are soft ferromagnets with high Curie temperatures, ranging from 700K to 1100K, allowing for applications at room temperature and above. The Curie temperatures are observed to vary almost linearly with the saturation magnetic moment which is also expected in half-metallic systems. First-principles calculations also predicted finite band gap in the minority spin channel for most of the alloys in Co2-xYxFeSi series. Fig. 2 shows the calculated density of states (DOS) plots using GGA approach for majority and minority spin channels of Co2-xMnxFeSi (0≤x≤1) alloys, where the Fermi level is represented by the zero energy. It can be seen clearly that the system exhibits half-metallic behavior after Mn substitution. In the case of parent compound CFS, there is significant amount of DOS at the Fermi level on both the spin channels. After Mn substitution, the Fermi level is observed to shift deeper in energy-levels and falls at the middle of the energy gap on spin down channel for x = 0.50. Further increase of Mn content shifts the Fermi level towards the lower edge of energy gap due to lattice expansion. But, still Fermi level lies within energy gap making the system Half-metallic. In addition, conduction band and valence band in majority spin channel touch each other at Fermi level in x = 1, making the system spin gapless semiconductor. The energy gap is observed to increase with the increase of Mn content. Although, the calculated minority spin gap is the highest for x = 1, the half-metallic gap is greater for x = 0.50. Relatively high mechanical hardness values among the reported Heusler alloys are also observed, approaching 16 GPa for the most Ti-rich material [6-8].

**References:**

1. C. Felser, G. H. Fecher, and B. Balke, Angewandte Chemie International Edition, 46, 668 (2007). 2. I. Galanakis, P. Dederichs and N. Papanikolao, Physical Review B, 66, 174429 (2002). 3. E. Fischer, J. Karel and S. Fabbrici, Physical Review B, 94, 024418 (2016). 4. L. Bainsla, A.I. Mallick and M.M. Raja, Physical Review B, 91, 104408 (2015). 5. Y. Jin, P. Khareland P. Lukashev, Journal of Applied Physics, 120, 053903 (2016). 6. R. Mahat, S. KC and U. Karki, Physical Review B, Submitted (2021). 7. R. Mahat, S. KC and D. Wines, Journal of Alloys and Compounds, 830, 154403 (2020). 8. R. Mahat, S. KC and D. Wines, Journal of Magnetism and Magnetic Materials, 521, 167398 (2021).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/7c947ceb5f0d173267903a665062a366.jpg)
Fig.1. The saturation magnetic moment versus valence electron counts per formula units with element Y = Ti, V, Cr, Mn, Fe, and Co in Co2-xYxFeSi (x = 0.50), both experimental and expected from Slater Pauling rule for half metals. The black data points represent reported literature values [3].

![](https://assets.underline.io/uploads/markdown_image/1/image/42867fe7839357c6b915951bb21bee55.jpg)
Fig.2. Spin polarized total DOS for Co2-xYxFeSi (Y = Mn, 0≤x≤1). Number of states is scaled with respect to one formula unit.

 Effect of mixing the low-valent transition metal atoms Y = Sc, Ti, V, Cr, Mn and Fe on the properties of quaternary Heusler compounds Co2-xYxFeSi (0≤x≤1)

Strongly correlated materials with multiple order parameters provide unique insights into the fundamental interactions in condensed matter systems and present opportunities for innovative technological applications. A class of antiferromagnetic honeycomb lattices compounds, A4B2O9 (A = Co, Fe, Mn; B = Nb, Ta), have been explored owing to the occurrence of linear magnetoelectricity. From our investigation of magnetoelectricity on single crystalline Co4Ta2O9, we discovered strongly nonlinear and antisymmetric magnetoelectric behavior above the spin-flop transition for magnetic fields applied along two orthogonal in-plane directions. This observation suggests that two types of inequivalent Co2+ sublattices generate magnetic-field-dependent ferroelectric polarization with opposite signs. The results motivate fundamental and applied research on the intriguing magnetoelectric characteristics of these buckled-honeycomb lattice materials.

**References:**

[1] N. Lee, D. G. Oh and Y. J. Choi, Scientific Reports, vol. 10, 12362 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/14735df7b8d80e6faf7c4ad0add6d601.jpg)
Fig. 1 Temperature dependence of the anisotropic ferroelectric polarization. (a–c) T dependence of Pa obtained by integrating the pyroelectric current after poling from 100 to 2 K in at Ha, Hb*, and Hc, respectively. Pa was measured at H = 1, 3, 5, 7 and 9 T. (d–f) T dependence of Pb* measured at Ha = 9 T, Hb*, and Hc, respectively. (g–i) T dependence of Pc measured at Ha = 9 T, Hb*, and Hc, respectively.

![](https://assets.underline.io/uploads/markdown_image/1/image/1dddc0b497f4c43b1b9e466269999736.jpg)
Fig. 2 Comparison of electric and magnetic properties. (a) Hb* dependence of Pa at T = 2 K. (b) Hb* dependence of the magnetodielectric effect along the a axis, MDa (%) = {ε′(H) − ε′(0T)} / ε′(0T) × 100 , measured with AC excitation of Ea = 1 V at f = 100 kHz and T = 2 K. (c) Hb* derivative of Mb* at 2 K.

 Highly nonlinear magnetoelectric effect in buckled honeycomb antiferromagnetic Co4Ta2O9

Introduction Multiferroic materials have been attracting much attention because they have multiple ordered (ferroelastic, ferroelectric, and ferromagnetic) states. In particular, magnetic and ferroelectric material has a property that magnetization M (electric polarization P) can be controlled by electric E (magnetic H) field. Such property is called “magnetoelectric (ME) effect”. In magnetic and ferroelectric material, there is also a possibility of observing an optical response that the rate of absorption is different between the cases that light enters from one direction and the opposite direction. Such a large nonreciprocal response in the visible light region was discovered in CuB2O4 [1]. The observed nonreciprocal response in light is thought to be originated from dynamical AC ME response. The present compounds, CaBaM4O7 (M=Co, Fe), have been attracting interest for their nontrivial magnetism because of the geometrically frustrated crystal structure consisting of triangular and Kagome layers. From the viewpoints of the studies of multiferroics, we have expected that the magnetic ordering couples with the spontaneous electric polarization P due to the crystal structure with a polar point-group of mm2. Indeed, we have observed the change of Pc induced by the weak ferromagnetic ordering in CaBaCo4O7 [2]. Then the magnetic-field Hab-induced giant variation in Pc was reported and the magnetostriction mechanism was proposed to explain the observed giant ME effect [3]. Also in the case of CaBaFe4O7, the ME coefficient Hαcc defined as △Pc=HαccHc with a maximum value of 39 ps/m was reported for the measurements of Hc-induced change of Pc at 80 K below the ferrimagnetic transition temperature of 275 K [4]. In this work, we have systematically investigated nonreciprocal DC ME response, i.e., crystalline (polar) direction dependence of ME coefficients for CaBaM4O7 (M=Co, Fe) single crystals. Especially, we focused on the electric-field (Ec)-induced magnetization (Mab or Mc) in CaBaM4O7 (M=Co, Fe), which had almost not yet been performed. Results and Discussion Figure 1 shows the Schematic crystal structure of CaBaM4O7 (M = Co, Fe). The space group of CaBaCo4O7 at room temperature is orthorhombic Pbn21, which is distorted and lowered symmetry from the higher one of hexagonal P63mc. Its (magnetic) point group is (m’m2’) mm2. Those of CaBaFe4O7 are Pbn21 and mm2, which are the same as CaBaCo4O7 [2,4]. Its magnetic point group is unknown yet. Both materials have quasi-triangular lattices and quasi-Kagome ones stacked along the c-axis direction. There exists multidomain structure within the orthorhombic ab plane in spite of no such one in the c axis. A spontaneous electric polarization along the c axis (Pc) is expected from the polar point group of mm2. Figure 2(i) shows the electric field dependence of the magnetization of CaBaCo4O7 in constant magnetic fields. The magnetic field (Hab) was applied within the magnetic easy ab plane perpendicular to the c axis, and the electric field (Ec) was applied along the c axis which is the direction of spontaneous electric polarization (Pc). The configuration among the external magnetic field, electric field, and crystalline direction (spontaneous electric polarizaion) is presented in the inset of Fig. 2(ii). When the electric field is applied in the parallel direction (p) to the crystalline direction, the magnetization increases as the electric field increases. Such trends can be clearly seen as solid symbols in Fig. 2(i). Conversely, in the antiparallel (a) case, the magnetization decreases with electric field (See open symbols). Figure 2(ii) shows the magnetic field dependence of Eα32 which is a component of linear ME tensor and defined as Mab≡Eα32Ec. Depending on the configurations between the electric field and the crystal direction, Eα32 shows opposite signs. The observed crystalline-direction (polarity) dependence of change in magnetization can be regarded as a DC nonreciprocal response. As is well known for the diode, nonreciprocal response is indispensable in device applications. Therefore, we explore the novel nonreciprocal phenomena as mentioned above in the present polar magnetic compounds, CaBaM4O7 (M = Co, Fe), for the future application such as “thermal diode”.

**References:**

[1] M.Saito et al., J. Phys. Soc. Jpn. 77, 013705 (2008). [2] H. Iwamoto et al., J. Phys: Conf. Ser. 400, 032031 (2012). [3] V. Caignaert et al., Phys. Rev. B 88, 174403 (2013). [4] V. Kocsis et al., Phys. Rev. B 93, 014444 (2016).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/ae2bea3298433e5c1ccf14561452cfc9.jpg)
Schematic crystal structure of CaBaM4O7 (M = Co, Fe) projected onto the bc plane (a). Its quasi-triangular (b) and quasi-Kagome layers (c) are projected onto the ab plane. The rectangular boxes represent the boundaries of unit cell [2].

![](https://assets.underline.io/uploads/markdown_image/1/image/0c8e519eab7cbb2fc00b2b326156b7ec.jpg)
(i) Electric field dependence of magnetization in CaBaCo4O7. Solid symbols correspond to the parallel configuration between the electric field and the crystalline (polar) direction, and open ones to the antiparallel configuration. (ii) Magnetic field dependence of Eα32 (≡Mab/Ec) deduced from the data shown in (i). The inset is a schematic diagram of the configuration among the external magnetic/electric fields and the crystal direction.

 Polarity dependence of change in electric polarization (magnetization) induced by magnetic (electric) fields in CaBaM4O7(M=Co, Fe) single crystals

In rare-earth orthoferrites, strongly correlated order parameters have been thoroughly investigated, which aims to find multiple fuctionalities such as multiferroic or magnetoelectric properties. We have discovered highly anisotropic and nonlinear magnetodielectric effect from detailed measurements of magnetoelectric properties in single-crystalline orthoferrite, ErFeO3. Isothermal dielectric constant varies in shapes and signs depending on the relative orientations between the external electric and magnetic fields, which may be ascribed to the spin-phonon couplings. In addition, a dielectric constant with both electric and magnetic fields along the c axis exhibits two symmetric sharp anomalies, which are closely relevant to the spin-flop transition, below the ordering temperature of Er3+ spins, TEr = 3.4 K. We speculate that the magnetostriction form the exchange couplings between Er3+ and Fe3+ magnetic moments would be responsible for this relationship between electric and magnetic properties. Our results present significant characteristics of the orthoferrite compounds and offer a crucial guide for exploring suitable materials for magnetoelectric functional applications.

**References:**

[1] H. J. Shin, Y.J. Choi and N. Lee, Scientific Reports., 10:11825 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/5564792e58f2025c698fb955501095ae.jpg)
Magnetodielectric effect of ErFeO3. Magnetodielectric (MD) effect defined as 
MD (%) = (ε′(H)−ε′(0T))/ε′(0T) × 100 for (a)–(c) a (MDa), (d)–(f) b (MDb), and (g)–(i) c (MDc) axes, respectively, at Ha, Hb , and Hc up to ± 9 T and T = 2 K.

![](https://assets.underline.io/uploads/markdown_image/1/image/7b3b7a8f4622c4c168fd19b029722ed0.jpg)
Temperature evolution of magnetodielectric effect along the c axis. (a)–(f) Hc dependence of MDc at T = 2, 2.5, 3, 3.5, 5 and 10 K. (g)–(l) Hc derivative of Mc and dMc/dHc measured at T = 2, 2.5, 3, 3.5, 5 and 10 K.

 Anisotropic and nonlinear magnetodielectric effects in orthoferritre ErFeO3 single crystals

The aim of this work is to establish the influence of deviation from oxygen stoichiometry on the properties of La-Sr manganites with manganese-substituting combination of divalent and quadrivalent ions having different electron configuration: Zn2+(3d10) and Ti4+(3p6). Polycrystalline manganites of La0.7Sr0.3Mn0.9(Zn2+0.5Ti4+0.5)0.1O3+γ compositions were prepared by ceramic processing. The sintering step was performed in air at 1473 K for 10 h. Obtained samples were then divided into three groups, which were exposed to heat treatments at 1223 K for 96 h at a partial pressure of oxygen in the gas phase of PO2 = 10-1 Pa, 10-8 Pa, and 101.3 kPa. All synthesized manganites were rhombohedral. Oxygen non-stoichiometry index (γ) of the samples of above-mentioned groups was calculated from the data on unit cell volume (V) according to algorithm proposed earlier [1] with the allowance for concentrations of Mn4+ and Mn3+ ions, anion and cation vacancies. As follows from Fig.1, unit cell volume decreases as a function of γ, and specific magnetization (σ) shows a tendency to increase almost within the measurement error. Temperature dependences of dμ(T)/dT, where μ(T) is magnetic permeability as a function of temperature T, are presented on Fig.2. Curie point defined as the temperature corresponding to the maximum of │dμ(T)/dT│, is equal to 219, 226, 229 K for manganites with values of γ = -0.008, 0.000, 0.009, respectively. One can see that temperature interval of “ferromagnetic-paramagnetic” transition is sufficiently wide (from 8 to 15 K), especially in stoichiometric manganite. Broadening of the transition interval can be associated with the formation of clusters, segregations, and magnetic inhomogeneities with various magnetization and transition temperature [2]. Manganite annealed in oxygen has the narrower transition interval than those annealed in vacuum, due to vacancy mechanism of cation diffusion, which smooths out spatial variations of the composition. Scanning electron microscopy studies have revealed the existence of microinhomogeneities having various configurations, including modulated structures. Manganite annealed at PO2 = 10-8 Pa has the highest absolute value of magnetoresistance: │MR│= 60 % in the field of 9.2 kOe at 120 K. Magnetostriction constant (λ) is maximal for a sintered sample having the oxygen non-stoichiometry index of γ = 0.004. At T = 140 K, it reaches gigantic value of λ = 7×10-3 and drops to 10-4 at 293 K. Interpretation of established regularities is discussed in terms of mechanisms of charge compensation with the allowance for formation of singly charged oxygen ions [3,4], diffusion processes, electron configuration and radii of substituents, double-exchange and Coulomb interactions.

**References:**

1. D. Merkulov, A. Badelin and V. Karpasyuk, Acta Physica Polonica A, Vol. 127, p.248 (2015) 2. V. Karpasyuk, A. Badelin, and I. Derzhavin, Journal of magnetism and magnetic materials, Vol. 476, p.371 (2019) 3. J. Mizusaki, N. Mori and H. Takai, Solid State Ionics, Vol. 129, p.163 (2000) 4. V. Karpasyuk, A. Badelin and D. Merkulov, Journal of Physics: Conference Series, Vol. 1347, p.012036 (2019)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/f309c2e6369525ef9191f175045927e6.jpg)
Fig.1. Dependencies of unit cell volume (1) and magnetization (2) on non-stoichiometry index

![](https://assets.underline.io/uploads/markdown_image/1/image/2031f433a7b459ba7ce2ed1f8ab2163f.jpg)
Fig.2. Temperature dependencies of dμ(T)/dT for manganites with γ = -0.008 (1); 0.000 (2); 0.009 (3)

 Structural and electromagnetic characteristics of La-Sr manganite with paired substitution of Zn and Ti for manganese depending on oxygen content

A strong coupling between spin, orbital, charge, and lattice degrees of freedom determines the unique properties of mixed valence manganites [1]. A phase separation phenomenon plays an important role in the physics of these materials [1, 2]. However, mechanisms of spontaneous phase separation are still not fully understood that does not permit to control the process by means of the external factors such as temperature, magnetic field, and pressure. The charge ordering (CO), which is the spatial ordering of the Mn3+ and Mn4+ ions, is closely related to the phase separation and is one of the most interesting phenomena observed in the mixed valence manganites. Herewith, the CO state is observed in the different materials with the R3+1-xA2+xMnO3 general formula [3, 4]. There are studies that indicate the martensitic nature of the charge ordering state in the mixed valence manganites [5, 6]. In this work, the polycrystalline films Pr1-xSrxMnO3 with x=0.2 and 0.4 were investigated in the temperature range of 100-390 K using the electron magnetic resonance (EMR) spectroscopy in the X-band and the magnetic susceptibility measurements. The films thickness is 100-130 nm. Single-crystal zirconium oxide stabilized by yttrium (YSZ) was used as the substrate. The samples were prepared by dc magnetron sputtering with the “facing-target” scheme that allows transferring elements from a target to a substrate without changes in the composition. The magnetic susceptibility data showed that the Curie temperature (TC) of the films is 115 K for x = 0.2 and 215 K for x = 0.4. These values are significantly lower than for the single crystals of the same composition (150 K and 300 K, respectively). This situation implies the presence of the phase separation in the films and the detection of possible magnetic correlations above Tc. The presence of the Griffiths-like phase in the films above their TC was previously established using analysis of the EMR spectra [7]. This phase represents the short-range ferromagnetic correlations in the paramagnetic region. The Griffiths temperature (TG) is 145 K for x = 0.2 and 295 K for x = 0.4 and corresponds to TC of the single crystals of the same composition. New research shows the presence of the CO state in the films above their TG. Temperature dependents of the inverse magnetic susceptibility measured for the samples in the external magnetic fields of H = 0.1 - 30 kOe demonstrate a pronounced shoulder in the wide temperature range up to values above room temperature. The example is shown in the Fig. 1 for the film with x = 0.4. It is should note that the pronounced shoulder above TG was also observed on the temperature dependence of the inverse residual magnetization of the films magnetized in the field of H = 500 Oe. In the case of the film with x = 0.4, the shoulder width as well as the temperature near the charge-ordering transition (TNCO) decreases with the growth of the applied magnetic field. The TNCO dependence on the applied magnetic field was traced. Inset in the Fig. 1 shows the TNCO (H) dependence for the film with x = 0.4. In the case of the film with x = 0.2, the inverse magnetic susceptibility above TG exhibits an ambiguous behavior in the high magnetic fields. For materials in the ferromagnetic region, the resonance line expands with decreasing temperature. The resonance line broadening observed for manganites above their TC (or TG) with increasing temperature is usually explained by the presence of spin-lattice relaxation and magnetic polarons. The temperature dependence of the resonance linewidth for the film with x = 0.2 indicates the presence of the charge ordering in the range of T = 200-350 K (Inset in the Fig. 2). For the film with x = 0.4, a maximum of about 350 K is also assumed (Fig. 2). The temperature hysteresis of the inverse magnetic susceptibility of the films is observed in the weak magnetic field above their TG. The example is shown in the Fig. 1 for the film with x = 0.4. This behavior is a direct evidence of the martensitic nature of the CO state [8]. The high-temperature charge ordering (TNCO = 600 K) was previously observed in the Bi-Sr manganite with x = 0.25 [3]. This behavior was explained by the exclusive role of the 6s2 electrons of Bi3+. The role of the 6s2 electrons of Pr3+ and the effect of intrinsic strains in the samples other than strains associated with grain boundaries or substrate lattice mismatch in films are discussed.

**References:**

1. E. Dagotto, T. Hotta, A. Moreo, Phys. Rep., Vol. 344, p. 1 (2001) 2. A. Krichene, W. Boujelben, S. Mukherjee, et al., Acta Materialia, Vol. 131, p. 491 (2017) 3. J.L. Garcia-Munoz, C. Frontera, M.A.G. Aranda, et al., J. Solid State Chem., Vol. 171, p. 84 (2003) 4. D.M. Polishchuk, A.I. Tovstolytkin, E.L. Fertman, et al., J. Magn. Magn. Mat., Vol. 410, p. 109 (2016) 5. V. Podzorov, B.G. Kim, V. Kiryukhin, et al., Phys. Rev. B, Vol. 64, p. 140406 (2001) 6. S. Dhieb, A. Krichene, N. Chniba Boudjada, et al., J. Phys. Chem. C, Vol. 124, p.17762 (2020) 7. Yu.E. Samoshkina, M.V. Rautskii, E.A. Stepanova, et al., J. Exp. Theor. Phys., Vol. 125, p. 1090 (2017) 8. X. Liang, J. Bai, J. Gu, et al., J. Mater. Sci. Technol,. Vol. 44, p. 31 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/e101268a634e7fa06dad7150320c4203.jpg)
Temperature dependences of the inverse magnetic susceptibility for the film with x = 0.4. The curves were measurement in two modes at H = 100 Oe: cooling (FC) and heating (FH). Inset: dependence of the temperature near the charge-ordering transition (TNCO) on the applied magnetic field. The squares are the experimental points, the line is the fit and approximation.

![](https://assets.underline.io/uploads/markdown_image/1/image/01cf1051a8b0d0dd510c299280e7246d.jpg)
Temperature dependence of the inverse magnetic susceptibility at H = 3 kOe and the resonance linewidth in the X-band for the film with x = 0.4. Inset: temperature dependence of the inverse magnetic susceptibility at H = 3 kOe and the resonance linewidth for the film with x = 0.2.

 High-Temperature Martensitic Transformation in Pr-Sr Manganites

Topological chiral semi-metal CoSi exhibit unusual quasi-particles excitations near the band crossing point, which have spin-1 and charge-2 chiral charge [1]. Like Dirac and Weyl semimetals, these semimetals also show some unusual electrical transport behavior, such as large magneto-resistance, mobility, and anomalous Hall effects. Therefore, we have performed temperature and magnetic field dependent electrical transport measurements on the topological chiral semimetal CoSi poly-crystals. We observed that while χ versus T indicates the paramagnetic nature of poly-crystals (inset of image1), 1/χ versus T behavior indicates that there is the presence of some weak antiferromagnetic exchange interaction at low temperature [2]. These poly-crystals show anomalous behavior in resistivity versus temperature measurements in the vicinity of such magnetic exchange interaction. The temperature and angle-dependent magneto-resistance (MR) measurements show negative behavior at low temperature, which is in contrast to the single crystal counterpart of CoSi, probably due to the presence of weak exchange interaction [3,4].

**References:**

 1. D. Takane, and T. Sato, Phys. Rev. Lett. 122, 076402, (2019). 2. Banik, S. et al. Phys. Rev. B 77, 224417 (2008). 3. X. Xu and S. Jia, Phys. Rev. B 100, 045104 (2019). 4. S.S Samatham, D Venkateshwarlu, and V Ganesan, Mater. Res. Express 1 026503, (2014).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/b58415af3c3b708d66c150d5bdbaeaab.jpg)
Temperature dependence of 1/χ showing the presence of exchange interaction at low temperature. Inset shows the temperature dependence of χ

![](https://assets.underline.io/uploads/markdown_image/1/image/18e6611ba53e53bfc851fc126014ccff.jpg)
Temperature-dependent magnetoresistance(MR) showing a change in MR from negative to positive as the temperature is increased

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