United States

First-order magnetic phase transitions (FOMPTs) generally occur due to concurrent discontinuous changes in magnetic and crystallographic sublattices. FOMPTs that involve changes in crystallographic symmetry are known as magneto-structural (MSTs), and they are commonly known as magneto-elastic (METs) when lattice symmetry remains invariant across the transition. Both MSTs and METs can give rise to plethora of functionalities. Here we report a peculiar magnetic phase transition in a lanthanide-based compound – Nd&lt;sub&gt;2&lt;/sub&gt;In – which is neither MST nor MET, but it has handful of features generally observed across FOMPTs. &lt;br/&gt;Nd&lt;sub&gt;2&lt;/sub&gt;In shows a non-hysteric paramagnetic-ferromagnetic transition with a nearly discontinuous change in magnetization at T&lt;sub&gt;C &lt;/sub&gt;~ 109 K, a typical FOMPT feature, and a broad second-order transition at ~52 K. The transition at T&lt;sub&gt;C&lt;/sub&gt; is also manifested as a sharp peak in heat capacity around T&lt;sub&gt;C&lt;/sub&gt; and much larger than recently reported&lt;sup&gt;1&lt;/sup&gt; magnetocaloric effect with the maximum calculated entropy change (ΔS) of -13 J/ Kg K in a 2 T magnetic field change. This behavior is qualitatively similar to other R&lt;sub&gt;2&lt;/sub&gt;In compounds where magnetoelastic FOMPTs are well established.&lt;sup&gt;2,3&lt;/sup&gt; Further, the temperature and magnetic field dependence of ΔS can be expressed as ΔS ~ H&lt;i&gt;&lt;sup&gt;n&lt;/sup&gt;&lt;/i&gt;, where the local exponent, &lt;i&gt;n&lt;/i&gt;, varies with both magnetic field and temperature, showing clear maxima with &lt;i&gt;n &lt;/i&gt;&amp;gt; 2, a characteristic feature of FOMPT.&lt;sup&gt;4&lt;/sup&gt; The temperature-dependent X-ray powder diffraction study, on the other hand, shows no evidence of lattice volume discontinuity or change of crystal symmetry across T&lt;sub&gt;C&lt;/sub&gt;.&lt;br/&gt;Acknowledgement: This work was performed at Ames Laboratory and was supported by the Division of Materials Science and Engineering of the Office of Basic Energy Sciences of the U.S. Department of Energy (DOE). Ames Laboratory is operated for the U.S DOE by Iowa State University under Contract No. DE-AC02-07CH11358.

2022 Joint MMM-INTERMAG

Peculiar magnetic phase transition and large magnetocaloric effect in Nd2In

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First-order magnetic phase transitions (FOMPTs) generally occur due to concurrent discontinuous changes in magnetic and crystallographic sublattices. FOMPTs that involve changes in crystallographic symmetry are known as magneto-structural (MSTs), and they are commonly known as magneto-elastic (METs) when lattice symmetry remains invariant across the transition. Both MSTs and METs can give rise to plethora of functionalities. Here we report a peculiar magnetic phase transition in a lanthanide-based compound – Nd2In – which is neither MST nor MET, but it has handful of features generally observed across FOMPTs. Nd2In shows a non-hysteric paramagnetic-ferromagnetic transition with a nearly discontinuous change in magnetization at TC ~ 109 K, a typical FOMPT feature, and a broad second-order transition at ~52 K. The transition at TC is also manifested as a sharp peak in heat capacity around TC and much larger than recently reported1 magnetocaloric effect with the maximum calculated entropy change (ΔS) of -13 J/ Kg K in a 2 T magnetic field change. This behavior is qualitatively similar to other R2In compounds where magnetoelastic FOMPTs are well established.2,3 Further, the temperature and magnetic field dependence of ΔS can be expressed as ΔS ~ Hn, where the local exponent, n, varies with both magnetic field and temperature, showing clear maxima with n &gt; 2, a characteristic feature of FOMPT.4 The temperature-dependent X-ray powder diffraction study, on the other hand, shows no evidence of lattice volume discontinuity or change of crystal symmetry across TC. Acknowledgement: This work was performed at Ames Laboratory and was supported by the Division of Materials Science and Engineering of the Office of Basic Energy Sciences of the U.S. Department of Energy (DOE). Ames Laboratory is operated for the U.S DOE by Iowa State University under Contract No. DE-AC02-07CH11358.

poster

Modification and control of magnetic anisotropy is crucial for the development of new permanent magnet materials, high density information storage, and many advanced spintronic applications. Enhanced anisotropy is often achieved via shape modification, stabilization of non-cubic crystal structures, or proximity effects such as exchange bias. An unusual proximity effect occurs at the interfaces of thin Co films adjacent to π-conjugated C60 fullerene films where initial field hysteresis loops exhibit a substantial asymmetry and considerable broadening at reduced temperatures [1]. We investigate these effects with temperature-dependent broadband ferromagnetic resonance (FMR). A key question in these studies is whether the C60-derived anisotropy affects the dynamical properties of the Co / C60 system including resonant fields, damping, and spectroscopic g-factors. We examine the magnetometry and FMR response of a Co [12 nm] / C60 [35 nm] / Nb [16 nm] sample as a function of temperature and field history. Conventional field hysteresis loops identify two main effects: the asymmetry is present only for the initial loop and the enhanced coercive field increases monotonically for temperatures below 200 K. Temperature-dependent FMR from 4 – 35 GHz confirm these observations. The effective magnetization (μ0Meff) tracks the increased anisotropy of the Co / C60 upon cooling, but following field cycling μ0Meff is reduced. The difference (Δμ0Meff) is as large as 26 mT at 10 K and Δμ0Meff drops to zero above 200 K. These effects are not observed in control samples with a Cu spacer layer inserted between the Co and C60 layers. Gilbert-type damping is slightly increased in the Co / C60 system at all temperatures, however, the enhanced anisotropy prior to field cycling has little effect on damping.

Anisotropy Enhancement in Co / C60 Fullerene Bi-Layers Determined by Ferromagnetic Resonance

The interest in the magnetic cooling devices has led to an intensive search for suitable well-performing magnetocaloric materials over the last 25 years. However, to this date only a few material systems have been found to be suitable for commercial applications. Computational screening makes possible sieving through thousands of known compounds without the need to perform time-consuming measurements and therefore can play an important role in detecting novel magnetocaloric materials. To identify such systems of interest we selected several screening parameters using properties of various well-known MCE materials as a reference. Along with magnetic properties, other factors important for practical applications were taken into consideration including price, availability, and toxicity of candidate materials. Combining these criteria, we implemented an algorithm for the screening process as a set of automated computational tools. It relies on information readily available in the structural databases to perform detailed modelling via ab-initio calculations. Two computational databases (Aflowlib and Materials Project) and two experimental databases (COD and ICSD) are used as initial source of information totaling to 800k candidate compositions. As a main metric to predict the magnetocaloric performance we use the magneto-elastic response of the candidate. This is done by computing magnetic moment of the material across a range of deformations, both volumetric and uniaxial. This parameter shows good correlation with ΔSM measured in known magnetocaloric materials. A step-by-step application of initial screening parameters to sort out unsuitable materials before performing more computationally heavy assessments allows us to quickly process large number of candidates. This resulted in a shortlist of promising compounds to serve as a guide for experimental research. The flexibility of the computational toolset makes it possible to easily build in additional screening parameters to further adjust or refine the search process.

An Efficient Strategy for the Discovery of Novel Magnetocaloric Materials

In recent years, magnetic refrigeration (MR) has gained much attention, rather than conventional gas refrigeration, being an energy efficient and eco-friendly technology. For that purpose, the current research for exploring potential magnetocaloric material is focused on the material exhibiting first-order magnetostructural transition (MST) along with large change in magnetization and hence large magnetocaloric effect (MCE) [1]–[3]. Recently, Ni-Co-Mn-Ti-based all d-metal Heusler alloy is found to be an excellent candidate for magnetic refrigeration which exhibits multicaloric properties such as MCE [4], elastocaloric effect [5], and giant barocaloric effect [6]. In the present work, we explore the effect of Sn doping at Ti-site and also heat treatment condition on MCE properties of Ni35Co15Mn37Ti13-xSnx (x = 0,1 and 2) alloys through thermal and magnetic measurements. The observed MST temperature (TM) shifts toward lower temperature with Sn doping whereas, the sharpness of the transition enhances with annealing time which effectively increases the MCE response as shown in fig.1 (a)). The sample with x = 1 exhibits a plateau-like magnetic entropy change (ΔSM) with a maximum peak value of ΔSM ~ 5.7 Jkg-1K-1 due to a magnetic field change of 50 kOe. It is interesting to note that ΔSM value remains almost the same with value ~ 4 Jkg-1K-1 for a temperature region of 300 K-350 K shown in fig.1 (b). Large ΔSM in a wide temperature interval is attributed to the existence of inter-martensite transition along with MST. The large ΔSM value with wide tunable operating temperature region in the vicinity of room temperature and the estimated large relative cooling power (RCP) of ~ 384 J/kg enable the material a suitable candidate for solid-state MR technology.

![](https://assets.underline.io/uploads/markdown_image/1/image/0742db6c7fcbb9ed5a3e2fcb08c45c88.jpg)

Figure 1: (a) Magnetization vs. T for x = 1 and 2alloys under different annealing temperatures. Inset shows DSC heat-flow vs. T with a ramp rate of 10 K/m of x = 1 sample.

![](https://assets.underline.io/uploads/markdown_image/1/image/2d9c91f1787e1efc24138fdba6d61ecd.jpg)

Figure 1: (b) ΔSM vs. T at different magnetic field for x = 1 alloy.

Large plateau-like Magnetic entropy change in Sn doped Ni-Co-Mn-Ti all d metal Heusler alloy

Gadolinium (Gd) films have been considered for micro and nano-scale application, because of their high magnetic moment and a Curie point close to room temperature (RT) [1]. Recently, free-standing thick films have been pointed out as promising active substance in energy conversion micro-devices [2] due to their magnetocaloric properties (MC). Indeed, as put in [2], good MC properties, surface quality, absence of substrate, and flexibility are the main features to get a caloric membrane to be deployed in a micro-electromechanical system (MEMS). Unfortunately, a systematic study of the optimal preparation parameters to obtain the aforementioned properties, is still lacking. Actually, film thickness, growth temperature, and the choice of the buffer layer, are all key features affecting the final result after substrate removal. Here, polycrystalline Gd films are prepared by sputtering on a silicon substrate with a thermally oxidized layer. Thickness of the film is varied from 100 nm to 17 μm, exploring growth temperatures in an interval between RT up to 666 K. Buffer layers of tungsten (W) and tantalum (Ta) are used. More than 45 Gd thick films with various growth temperatures, thicknesses and buffer layers have been prepared. The first result is that notwithstanding the growth temperature and thickness, tungsten buffer makes the substrate removal more difficult, particularly over large film surfaces (e.g. tens millimetres size). Increasing the growth temperature improves the magnetic properties [3] and changes the surface morphology. For instance, surface roughness is 10 nm and 121 nm for films prepared at 543 K and 666 K, respectively. Using tantalum, wide area free-standing films of various thicknesses from 5 to 17 μm have been obtained, with a flexibility depending on the growth temperature. Thinner free-standing films, namely 3 μm Ta/Gd/Ta have also been obtained showing smaller sizes (i.e. few millimeters size). In summary, the main result here is the identification of optimal preparation conditions (buffer layer, growth temperature and thickness) to obtain large, smooth and flexible Gd films to be used in MEMS device as a magnetocaloric membrane.

Producing gadolinium free-standing and flexible films, with high quality surface for energy applications: the role of thickness and growth temperature

ABO3 type compounds with perovskite structure are known to exhibit a very rich variety of phase transitions ranging from ferroelectric, antiferroelectric, ferrielectric, antiferrodistortive octahedral tilt, ferromagnetic, antiferromagnetic, ferrimagnetic, John-Teller, metal-insulator and superconducting transitions [1]. The richness of these phenomena is further enhanced by introducing substitutional disorder at the A or B sites leading to relaxor ferroelectricity, dipole-glass, spin-glass and quantum phase transitions [2]. The technological applications of these perovskites is due to the functional properties imported by such phase transitions. In this context, the B-site disordered iron-niobate family has evinced considerable interest due to the temperature stable giant dielectric constant and multiferroicity. The low temperature magnetic transitions and the ground state of these complex perovskites is now fully understood [3,4]. However, understanding of the high temperature behaviour is still lacking. In the present investigation, we report high temperature phase transitions in Sr(Fe1/2Nb1/2)O3 (SFN) using dc magnetization and x-ray diffraction measurements. Our dc magnetization M (T) study reveals two magnetic transitions around 620 K and 700 K for the first time. The magnetic transition occurring around 620 K is linked with the structural phase transition as confirmed by temperature dependent x-ray diffraction studies. The integrated intensity of the strongest superlattice reflection (ISL) and the octahedral tilt angle (φ) decrease continuously with increasing temperature and vanishes across the structural phase transition. We have fitted temperature variation of both ISL and φ using the expressions B(TC-T)β and B(TC-T)2β, respectively, where B is constant, TC is the structural phase transition temperature and β is critical exponent. The value of β comes out to be 0.24 which suggests the tricritical nature of the phase transition. Another transition around 700 K in the M (T) plot occurs close to the peak temperature in the loss tangent (tanδ). We believe that this transition is most likely driven by oxygen vacancies.

![](https://assets.underline.io/uploads/markdown_image/1/image/6e631abc07abd6eec3192e6391959901.jpg)

DC magnetization versus temperature plot of Sr(Fe1/2Nb1/2)O3 at 100 Oe field

Magneto-structural phase transition in the B-site disordered Sr(Fe1/2Nb1/2)O3 perovskite: A combined dc magnetization and x-ray diffraction study

Magnetocaloric effect is a new nonconventional method that can be used to provide cooling power with several benefits compared to conventional gas-compression based cooling. Heusler alloys are promising candidates for micro-magnetic cooling applications thank their desirable behaviour. Preparation of Heulser alloys in a form of glass-coated microwires by the Taylor-Ulitovsky technique allows easy and fast production of microwires with protective glass coating and many additional advantages such as scalability of the size of cooling material. Previous works show the possibility of tuning the structural and magnetic transformation temperature of glass coated Heusler microwires by changing the chemical composition and valence electron concentration ratio e/a. This is one of the most favourable properties of glass coated Heusler microwires. Combining structural and magnetic transformation may enhance the amplitude of the magnetocaloric effect when both transformations overlap, the evaluation of their contribution may become complicated. Therefore, we would like to present the possible analyses which can provide information about the magnetocaloric effect or the transformation temperatures including both structural and magnetic transitions. Direct measurements of magnetocaloric effect, indirect measurement of magnetocaloric effect, resistivity measurements, Arrott plot method, universal curves, method of critical exponent n, Kouvel-Fisher method with Arrott-Noakes plots and many others can be used to study the magnetocaloric effect and transformations on a presented group of alloys. This research was supported by Slovak Grant Agency VEGA 1/0053/19, Slovak Grant Agency grant number APVV-16-0079.

Magnetocaloric Effect Study on Heusler Based Glass-Coated Microwires

Mn0.5Fe0.5NiSi0.95Al0.05 is a member of the MnTX (T = Ni, Co; X = p-block elements) family of intermetallic compounds. It exhibits a first-order ferromagnetic transition coupled with a structural phase transition at 315 K. Near this transition a large magnetic entropy changes of ~17 J kg-1 K-1, for a field change of ΔH = 2 T, has been reported for Mn0.5Fe0.5NiSi0.95Al0.05.[1] In this work, we present an experimental study on the crystalline, magnetic, and magnetocaloric properties of Ni deficient (Mn-rich) Mn0.525Fe0.5Ni0.975Si0.95Al0.05. The study has been performed by x-ray diffraction, scanning electron microscopy, and dc magnetization measurements. X-ray diffraction measurements showed that the sample simultaneously exhibited the orthorhombic and hexagonal structures at room temperature. The ferromagnetic transition temperature occurred at ~338 K, which is significantly larger than 315 K observed in Mn0.5Fe0.5NiSi0.95Al0.05. A maximum magnetic entropy changes of ΔSM = -9.5 and 25 J kg-1K-1 for ΔH = 2 T and 5 T, respectively, has been observed. Reasonably large refrigeration capacity of 60 J /kg and 160 J/kg for field changes of ΔH = 2 T and 5 T, respectively, has also been observed. The experimental results and related discussions will be presented in detail. Work at SUNY, Buffalo State was supported by the startup fund from SUNY Buffalo State College and Undergraduate Summer Research Fellowship award, Undergraduate Research Office, Buffalo State.

Near room temperature magnetocaloric properties in Ni deficient Mn0.525Fe0.5Ni0.975Si0.95Al0.05

Magnetic cooling obtained from magnetocaloric (MC) effect can be used as a substitute to usual refrigeration [1]. Recently, few reports illustrated the MC effect in Gd based compounds [1-2]. Das et al. [2], found the MC effect in exchange frustrated bulk magnet, GdCrTiO5, where the origin of strong frustration is due to exchange interaction of Gd3+ and Cr3+ sublattices. There are limited reports on the magnetic properties of bulk GdCrTiO5 [2-4], but none focused on the nano-dimension. Therefore, in the present case, the structural and magnetic properties of sol-gel synthesized and subsequent calcined (at 800 °C) GdCrTiO5 nanoparticles were explored. The synthesized GdCrTiO5 nanoparticles stabilizes in a orthorhombic crystal structure with space group Pbam, with lattice parameters, a, b, c of 7.381(2), 8.679(2), 5.862(2) Å, respectively, as confirmed from the x-ray diffraction measurements. The transmission electron microscopy shows the particle size as 37 ± 1 nm. The temperature dependence of dc magnetization, M(T), was measured for GdCrTiO5 nanoparticles and the Néel temperature, TN = 190 ± 2 K, obtained. At low fields, the spins of the Cr and Gd align in opposite directions to each other and the net moment align in the opposite direction to the applied field, in the temperature range 10 to 108 K. Additionally, spin reorientation is observed at temperature of TSR = 17 ± 3 K. Irreversibility appeared in field-cool-cooling (FCC) and field-cool-warming (FCW) curves at low temperatures, indicating a ferromagnetic-antiferromagnetic (FM-AFM) transition. This FM-AFM transition and TSR was not observed in bulk GdCrTiO5 [2-4]. Both FM nature and exchange bias effect is further established from the field-dependent magnetization measurements. Furthermore, a change in isothermal magnetic entropy (-ΔSm) of 22 ± 3 J.kg-1.K-1 is found below 10 K, for a 7 T change in field. The obtained magnetic properties in this report are discussed in terms of exchange frustration originating from the competing interactions of the magnetic sublattices of the Cr3+ and Gd3+ in the GdCrTiO5 nanoparticles.

![](https://assets.underline.io/uploads/markdown_image/1/image/426fc49bea4c68ae303d0c9fb7b3f46d.jpg)

Fig. 1. M(T) data for GdCrTiO5 nanoparticles.

Anomalous Magnetic Properties of GdCrTiO5 Nanoparticles

In this paper, we report the variations observed in magnetothermal, magnetocaloric, and magnetic properties of the Gd2In1-xGex (0 ≤ x ≤ 0.2) system of compounds concerning the changes in substitution of Ge. Changes have been recorded in a temperature sweeping range of 2-300 K while the magnetic field was increased from 0 to a maximum of 5 T. All the compositions set into the Ni2In-type hexagonal structure and no structural changes are observed with the change in the value of x. Though the transition temperature values, which are TC ≈ 191 K and TN ≈ 100 K in case of x = 0, have only subtle shifts with the Ge substitution yet promising changes have been observed in the magnetocaloric effect. At x = 0.2 the isothermal magnetic entropy variation peak touches the value of ~ 2.5 J/kg.K in a field change from 0 to 5 T. This showcases that the compounds reported can meet the challenge of the influential applicants in the race of magnetocaloric compounds.

![](https://assets.underline.io/uploads/markdown_image/1/image/4724d1db55dd31b90895358fbd9adc22.jpg)

First derivative of the magnetization curve of the compound Gd2In0.8Ge0.2 revealing the transition temperature clearly. The TN (Néel temperature) is the antiferromagnetic transition temperature while TC (Curie temperature) is the ferromagnetic transition temperature.

![](https://assets.underline.io/uploads/markdown_image/1/image/c153c4dca4cd946b35e4fb0d2350021a.jpg)

Change in isothermal magnetic entropy vs. temperature for the Gd2In1-xGex (0 ≤ x ≤ 0.2) system of compounds in the vicinity of TN.

Modifications in the magnetocaloric effect owing to composition changes in Gd2In1-xGex (0 ≤ x ≤ 0.2) system of compounds

Rare-earth orthochromites (RCrO3, R = rare-earth element) with a distorted perovskite structure have attracted attention due to their unusual physical properties, including temperature-induced magnetization reversal, spin-reorientation, spin-flipping, Magneto-caloric effect (MCE), and exchange-bias [1]. These materials represent a new class of multiferroic, which exhibit the coexistence of ferroelectric and magnetic orders below the Néel temperature (TN) [2]. It has been found that the magnetic behavior of RCrO3 compounds is strongly influenced by the Cr3+–Cr3+ super-exchange interaction rather than the R3+–Cr3+ and R3+–R3+ super-exchange interactions [1, 3]. In this contribution, the structural and magnetic properties of magneto-caloric DyCrO3 are studied. The sample was prepared by sol-gel method and calcined at 900 °C to yield an average particle size of 175 ± 10 nm with an average crystallite size of 65.07 ± 0.06 nm and lattice strain of 0.0038 ± 0.0006, as determined from transmission electron microscopy (TEM) and Williamson-Hall analysis of x-ray diffraction patterns, respectively. Rietveld refinement of the powder x-ray diffraction patterns was performed using GSAS software (Fig. 1), based on centro-symmetric space group Pbnm. Magnetization measurements as a function of temperature, with different probing magnetic fields, were carried out to determine the various magnetic transitions in the sample under zero field cooled (ZFC) and field cooled (FC) modes (Fig. 2). DyCrO3 orders AFM ascribed to the Cr magnetic order at TNCr ≈ 147 K. The magnetization increases for T &lt; TNCr. This is the paramagnetic response of Dy3+ ions, as these continuously rotate to align with the Cr3+, before the Dy3+ order at TNDy at about 5 K [4]. This magnetic transition contributes to the MCE of DyCrO3.This behavior is in agreement with previously reported values [5]. The transition temperatures observed in the curves are validated with measurements. The cause of observed anomalies in magnetic transition will be discussed considering the magnetic interactions and structural changes.

![](https://assets.underline.io/uploads/markdown_image/1/image/337c315947dc543b01368af5183af4ab.jpg)

Fig. 1

![](https://assets.underline.io/uploads/markdown_image/1/image/28b3b93b5c44ff7ab8b854447a9a183d.jpg)

Fig. 2

Peculiar magnetic phase transition and large magnetocaloric effect in Nd2In

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