United States

Solid-state refrigeration materials have various thermal effects, among which the hydrostatic pressure is an economical and practical method to drive the barocaloric effect (BCE) of brittle materials[1,2]. The BCE is ubiquitous in first-order phase transition materials, and its packaging technology is not limited to the shape of the materials[3,4]. In the brittle magnetocaloric materials MnCoGe&lt;sub&gt;0.99&lt;/sub&gt;In&lt;sub&gt;0.01&lt;/sub&gt;, there is a low-pressure induced large reversible BCE near room temperature, which avoids part of the refrigeration capacity reduction caused by hysteresis loss[5].&lt;br/&gt;Here, we report the BCE of MnCoGe&lt;sub&gt;0.99&lt;/sub&gt;In&lt;sub&gt;0.01&lt;/sub&gt; at hydrostatic pressure of 1kbar by variable-pressure calorimetry. Fig.1a shows the temperature dependence of the heat capacity &lt;i&gt;dQ/dT&lt;/i&gt; of MnCoGe&lt;sub&gt;0.99&lt;/sub&gt;In&lt;sub&gt;0.01&lt;/sub&gt; at different hydrostatic pressures after baseline subtraction, it can be found that the thermal hysteresis (Δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;hys&lt;/sub&gt;) at 1bar is 8.8K and the phase transition temperature moves to lower temperature with the increase of pressure. The linear fitting relationship between the transformation temperature shifts with the pressure (&lt;i&gt;dT/dP&lt;/i&gt;) is obtained according to the heating and cooling transformation temperature under different pressures, as shown in the inset of Fig. 1b. The &lt;i&gt;dT/dP&lt;/i&gt; is -10.6K/kbar in the heating process and is -8.7K/kbar in the cooling process. The entropy curve &lt;i&gt;S&lt;/i&gt;(T,P) of MnCoGe&lt;sub&gt;0.99&lt;/sub&gt;In&lt;sub&gt;0.01&lt;/sub&gt; during heating and cooling process was obtained by the calorimetric curves(Fig. 1a) through the pressure-dependent integrations across the phase transition, as shown in Fig.1b. We evaluated the reversible parts (Δ&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;rev&lt;/sub&gt; and Δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;rev&lt;/sub&gt;) of entropy change Δ&lt;i&gt;S&lt;/i&gt; and adiabatic temperature change Δ&lt;i&gt;T&lt;/i&gt;&lt;i&gt; &lt;/i&gt;at 1kbar from the overlapping of the irreversible Δ&lt;i&gt;S&lt;/i&gt; and Δ&lt;i&gt;T&lt;/i&gt; during application and removal of pressure, as shown in Fig.1c and 1d, where the shaded areas represent the Δ&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;rev&lt;/sub&gt; and Δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;rev&lt;/sub&gt;, respectively. The relative narrow Δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;hys&lt;/sub&gt; and high driving rate&lt;i&gt; dT/dP &lt;/i&gt;under pressure are more conducive to achieve large Δ&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;rev&lt;/sub&gt; and Δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;rev&lt;/sub&gt;. The Δ&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;rev&lt;/sub&gt; of 19J/kg K and Δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;rev &lt;/sub&gt;of 2.9K within a temperature span of 56K at 1kbar have been achieved. The refrigeration capacity of MnCoGe&lt;sub&gt;0.99&lt;/sub&gt;In&lt;sub&gt;0.01&lt;/sub&gt; at 1kbar is as high as 373J/kg K.

![](https://assets.underline.io/uploads/markdown_image/1/image/f5b2d3fe1b51b27d3f3361529defdc74.jpg)

Fig.1.For MnCoGe0.99In0.01, a)dQ/dT, b)S, c) ΔSrev, d)ΔTrev.



2022 Joint MMM-INTERMAG

Large room-temperature reversible barocaloric effect in MnCoGe0.99In0.01 alloys at low pressure

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

Solid-state refrigeration materials have various thermal effects, among which the hydrostatic pressure is an economical and practical method to drive the barocaloric effect (BCE) of brittle materials[1,2]. The BCE is ubiquitous in first-order phase transition materials, and its packaging technology is not limited to the shape of the materials[3,4]. In the brittle magnetocaloric materials MnCoGe0.99In0.01, there is a low-pressure induced large reversible BCE near room temperature, which avoids part of the refrigeration capacity reduction caused by hysteresis loss[5]. Here, we report the BCE of MnCoGe0.99In0.01 at hydrostatic pressure of 1kbar by variable-pressure calorimetry. Fig.1a shows the temperature dependence of the heat capacity dQ/dT of MnCoGe0.99In0.01 at different hydrostatic pressures after baseline subtraction, it can be found that the thermal hysteresis (ΔThys) at 1bar is 8.8K and the phase transition temperature moves to lower temperature with the increase of pressure. The linear fitting relationship between the transformation temperature shifts with the pressure (dT/dP) is obtained according to the heating and cooling transformation temperature under different pressures, as shown in the inset of Fig. 1b. The dT/dP is -10.6K/kbar in the heating process and is -8.7K/kbar in the cooling process. The entropy curve S(T,P) of MnCoGe0.99In0.01 during heating and cooling process was obtained by the calorimetric curves(Fig. 1a) through the pressure-dependent integrations across the phase transition, as shown in Fig.1b. We evaluated the reversible parts (ΔSrev and ΔTrev) of entropy change ΔS and adiabatic temperature change ΔT at 1kbar from the overlapping of the irreversible ΔS and ΔT during application and removal of pressure, as shown in Fig.1c and 1d, where the shaded areas represent the ΔSrev and ΔTrev, respectively. The relative narrow ΔThys and high driving rate dT/dP under pressure are more conducive to achieve large ΔSrev and ΔTrev. The ΔSrev of 19J/kg K and ΔTrev of 2.9K within a temperature span of 56K at 1kbar have been achieved. The refrigeration capacity of MnCoGe0.99In0.01 at 1kbar is as high as 373J/kg K.

![](https://assets.underline.io/uploads/markdown_image/1/image/f5b2d3fe1b51b27d3f3361529defdc74.jpg)

Fig.1.For MnCoGe0.99In0.01, a)dQ/dT, b)S, c) ΔSrev, d)ΔTrev.

technical paper

The M5XB2 materials system has been widely studied as permanent magnetic materials[1] [2]. As permanent magnetic materials, their coercivity and magnetic energy product are lower than those of the mainstream permanent magnetic materials. Xie et al.[3] and Cedervall et al.[4] proposed that the Mn5PB2 and (Fe1-xCox)5PB2 compounds have the prospect of being applied as magnetocaloric materials due to their near room temperature Curie temperature. In this work, the structure and magnetocaloric properties of the Mn5(SiP)B2 compounds of the M5XB2 material system were studied. According to a refinement of the XRD data the Mn5(Si1-xPx)B2 compounds all crystallize in the Cr5B3–type body-centered tetragonal structure, with a small amount of Mn2P as a secondary phase (less than 7%). The lattice parameters and the unit-cell volume of the compounds change linearly with the increase in P content. These experimental results are consistent with calculated DFT results. The Curie temperature of the compounds can continuously be adjusted between 305 and 411 K by changing the Si/P ratio. The introduction of P also caused a decrease in saturation magnetization. The magnetic phase transition of these compounds was determined using Arrot plots and the field exponent n for the magnetic entropy change based on Landau's theory. The studied compounds all show a second-order magnetic phase transition. Since the compounds show a second-order phase transition, the magnetic entropy change caused by the phase transition was not large: 1.9 and 1.4 J/kgK for Mn5SiB2 and Mn5PB2, respectively. However, the advantage of this series of compounds is that the Curie temperature can be adjusted continuously around room temperature.

![](https://assets.underline.io/uploads/markdown_image/1/image/1d9940cac68d7c5951d382a4b1969178.jpg)

Fig. 1. Temperature dependence of magnetization of Mn5(Si1-xPx)B2(0 ≤ x ≤ 1) in a field of 0.01T.


![](https://assets.underline.io/uploads/markdown_image/1/image/a3a6abe7d32a72ba069affbbfed1f01d.jpg)

Fig. 2. TC as a function of P content for Mn5(Si1-xPx)B2 (0 ≤ x ≤ 1).

Magnetocaloric Properties of a New Type of Magnetocaloric Materials - M5XB2 System

La(Fe, Si)13 is a promising candidate for magnetocaloric based technology such as magnetic refrigeration or energy harvesting [1-3]. This alloy family consists of a low content of rare earth (7.1 at. %) and high content of iron, resulting in a cheap and non-toxic compound. La(Fe, Si)13 based alloys exhibit a large magnetocaloric effect (MCE) at the transition between ferromagnetic and paramagnetic states, which occurs at Curie temperatures (Tc) ranging between 200-259K [4]. The magnetic properties (Tc, magnetization, MCE), the crystal structure (cubic or tetragonal) and the type of transition can be tuned by adjusting the Si content. Furthermore, the Curie temperature can be increased to above room temperature by doping and hydrogenation [5]. Recently our group reported for the first time the possibility to fabricate thick films of La(Fe, Si)13 [6]. Here we present a study on compositionally graded films of La-Fe-Si. The films were fabricated by triode co-sputtering of three targets (La-Fe, Fe, Si-Fe) onto thermally oxidised stationary Si substrates (100 mm in diameter). The composition of the as-deposited films was mapped by EDX, as shown in Fig. 1. The films were annealed ex-situ in a rapid thermal annealing furnace at 900°C. For each film, we selected samples from specific regions for characterization using optical and scanning electron microscopy, VSM-SQUID magnetometry and X-ray spectroscopy. Fig. 2 displays M(T) measurements on four La-Fe-Si samples of 5 μm thickness, taken from the regions specified in Fig. 1. The presentation will report results from films of nominal thickness ranging between 150nm – 5μm. The presentation will give details about how the structural and magnetic properties vary as a function of film composition, thickness and annealing conditions. Prospects for further developments and possible applications will also be discussed. Acknowledgement: This research has received funding from the French National Research Agency under the HiPerTherMag project (ANR-18-CE05-0019).

![](https://assets.underline.io/uploads/markdown_image/1/image/e47b4016b72ccd38f00fea3375cd00d9.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/a06f84bea07fbcfb4eb5845d9b87a6ea.jpg)

Compositionally graded La-Fe-Si films

Compositionally graded La-Fe-Si films

The LaFe13-xSix compounds have been studied for nearly two decades for their potential to serve as materials for magnetocaloric cooling. They exhibit either first- or second-order phase transitions depending on x(Si). Here we present the discovery of a naturally formed two-phase composite at the LaFe2Si stoichiometry, which exhibits strongly responsive behaviors without mechanical degradation that can be exploited in weak magnetic fields. Some of the unusual properties include a two-step, nearly anhysteretic first-order phase transformation between ferromagnetic (FM) and paramagnetic (PM) states, instead of a singular phase change present in conventional LaFe13-xSix, that is preserved in magnetic fields as high as 100 kOe. In addition to the giant magnetocaloric effect, the title material exhibits large, plateau-like positive magnetoresistance, both extending over a much wider temperature range when compared to phase-pure LaFe13-xSix. Finally, the composite also shows a Griffiths-like phase associated with short-range FM clustering in the PM state (Pathak et. al., Acta Mat. 215 (2021) 117083). We will also discuss the effect of impurities on magnetic, magnetocaloric, and transport behaviors of LaFe2Si. The work at Ames Laboratory was supported by the Division of Materials Science and Engineering, the Office of Basic Energy Sciences of the DOE. Ames Laboratory is operated for the U.S DOE by Iowa State University under Contract No. DE-AC02-07CH11358. Work at SUNY, Buffalo State was supported by the startup fund from SUNY Buffalo State College and the Undergraduate Research Office, Buffalo State.

Unusual magnetic, magnetocaloric, and transport properties in phase-separated LaFe2Si

High-entropy alloys (HEAs), based on the design concept of mixing five or more principal elements to yield high entropy of mixing (ΔSmix), expands the compositional space of multicomponent materials when compared to conventional materials, which are mainly based on one or two main constituents. HEAs, thus, form compositions without dominant elements, in which new materials with excellent properties, some of them being superior or unique compared to the conventional materials, have been found [1]. These advantages prompted a large surge in studying HEAs, with the explored compositions evolving from first-generation single phase equiatomic to second-generation multiphase non-equiatomic HEAs. The latter are recently reported with properties that outdo those of the first-generation HEAs, such as excellent strength-ductility combination, surpassing the low temperature limit, or enhanced magnetocaloric properties of rare-earth-free high-entropy alloys owing to a first-order magnetic phase transition [1-3]. Here, we present, when tuning CoCrMnNiTi alloys from conventional to the high-entropy region (i.e. ΔSmix &gt; 1.5 R, where R is the gas contstant, 8.314 J mol-1 K-1), the evolution of their thermomagnetic and magnetocaloric behavior. The obtained HEA has a martensitic temperature tuned nearer to room temperature and a 10% increase in the entropy change (Fig. 1). This work demonstrates the recently proposed claim [1-3] that it is possible to obtain high-performance magnetocaloric materials within the HEA compositional space. Work supported by AEI/FEDER-UE (grant PID2019-105720RB-I00), US/JUNTA/FEDER-UE (grant US- 1260179), Consejería de Economía, Conocimiento, Empresas y Universidad de la Junta de Andalucía (grant P18-RT-746), Army Research Laboratory under Cooperative Agreement Number W911NF-19-2-0212 and Sevilla University under VI PPIT-US program.

![](https://assets.underline.io/uploads/markdown_image/1/image/ac398a967db02e43d38fa8ceed0d87a5.jpg)

Fig 1. The variation of martensitic transition temperatures (square symbols) and entropy change at the transition (circular symbols) after tuning a conventional alloy towards the high-entropy region (ΔSmix > 1.5 R).

Tuning conventional alloys towards the high-entropy space: thermomagnetic and magnetocaloric behavior

Magnetic refrigeration is an energy-efficient, environmentally-friendly alternative to conventional vapor-compression cooling technology. There are several magnetic cooling device designs in existence today that are potentially commercially viable, on condition that that suitable working materials can be developed. This challenge is unresolved due to issues associated with shaping the mostly brittle magnetocaloric alloys into thin-walled channeled regenerator structures to facilitate efficient heat transfer between the solid refrigerant and the heat exchange fluid in an active magnetic regenerator (AMR) cooling device. To address these challenges, we have developed an extrusion-based additive manufacturing (AM) method to 3D print porous magnetocaloric structures.1 This AM technique’s novelty lies in the initial material feedstock comprising of magnetic particles (upto ~ 85 wt%) and sacrificial polymer binders dispersed in a multi-solvent system. While the solvents control the ink rheology, the polymers bind the magnetic particles, enabling retention of the regenerator architecture. Next, a two-step sintering process removes the binder and subsequently promotes grain growth and densification of the final finished part. Research efforts involving La0.6Ca0.4MnO3 nanoparticles will be presented. Figure 1 shows that the magnetocaloric response (indicated by the magnetic entropy change) of the 3D printed test scaffold is only ~17% lower than that of the precursor particles. Spatially designed structures with channel dimensions of 150 µm were obtained to exhibit the effectiveness of this fabrication process. The microstructures and porosity of the as-printed and sintered samples will be discussed in the context of results obtained via 3D X-ray computed tomography. Overall, this study provides strategies for realizing low-cost magnetic regenerators, thus potentially eliminating one of the main barriers to commercialization of magnetic cooling technology.

![](https://assets.underline.io/uploads/markdown_image/1/image/40b0fbbd914b91dd6f4cee2961b48796.jpg)

Extrusion-Based 3D Printing of Magnetocaloric Structures

The possibility of inducing a structural martensitic transformation by applying a magnetic field in meta-magnetic shape memory alloys gives rise to interesting properties such as magnetic actuation, giant magnetoresistance, or giant inverse magneto-caloric effect, which make these alloys very attractive for practical applications in sensing and magnetic refrigeration. Composites made from polymer matrix with meta-magnetic shape memory powder have been recently proposed to overcome the intrinsic brittleness of the bulk alloys. This, in fact, opens the possibility of the use of particles for additive manufacturing purposes. The production, characterization, and optimization of the properties of powder particles are therefore milestones to get valuable functional composites. In the present work, the martensitic transformation and the magnetic properties of Ni45Co5Mn37In13 powder microparticles obtained by ball milling have been studied. Even for very large milling times, a considerable dispersion in the particle size is observed in all the samples. Nevertheless, it is found that the characteristic of the transformation and the magnetic response is exactly the same in those particles with the same particle size, irrespective of the milling time. A direct correlation between size and deformation can be then established, from which the effect of mechanically induced microstructural defects on the magnetism is analyzed. The effect of mechanically induced defects on the magnetocaloric effect and the viability of the use of the studied microparticles for composite elaboration are also analyzed. Polymer composites have been elaborated by embedding the micro/nanoparticles in a mixture of polylactic acid(PLA) and poly-caprolactone(PCL). In order to get 3D printable wires with optimum mechanical properties and good magnetic response, the particles size, polymers fractions, and particles concentration have been varied. The magnetic response and printability of the obtained filaments have also been studied.

![](https://assets.underline.io/uploads/markdown_image/1/image/4c365c47c2173f24fd05b88fc85de5e6.jpg)

Multifunctional magnetic composites based in meta-magnetic shape memory alloys for 3D printing applications

Multifunctional magnetic composites based in meta-magnetic shape memory alloys for 3D printing applications

The use of composites combining a thermoplastic and functional fillers for additive manufacturing (AM), as in fused deposition modeling, FDM, provides a path for low cost development of functional parts with complicated geometries [1]. Magnetic refrigeration requires refrigeration beds with intricate geometries for the passage of the heat transfer fluid. Heusler alloys exhibiting magneto-structural transformation (MST) are attracting enormous attention as they can show a large response without relying on critical elements [2]. However, machinability of these alloys is compromised, making AM attractive for the fabrication of the refrigerator beds. Off-stoichiometry Ni2MnGa Heusler powder has been obtained by ultrasonic atomization, resulting in spheric particles subsequently sieved at 100 μm (Fig. 1). Differential scanning calorimetry (DSC) enabled to identify the MST in the atomized Heusler alloy (Fig. 2(a)). This powder was used to fill customized PLA capsules that were used as the feedstock for the extrusion of composite filaments for FDM according to the method showed in Ref. [3]. Composite filaments were manufactured with different concentrations of fillers ranging from 30 to 64 wt. %, determined by thermogravimetric analysis, TGA, (Fig. 2(b)). As the particles were not subjected to high temperatures during the extrusion of the filaments (less than 200 °C) , the phases present in the alloy do not change. The AM of magnetocaloric parts can avoid the shape limitation and, in this case, the polymer matrix would prevent the weakening of the structure due to the successive volume changes taking place with the cyclical occurrence of an MST. Work supported by AEI/FEDER-UE (grant PID2019-105720RB-I00), US/JUNTA/FEDER-UE (grant US-1260179), Consejería de Economía, Conocimiento, Empresas y Universidad de la Junta de Andalucía (grant P18-RT-746), Army Research Laboratory under Cooperative Agreement Number W911NF-19-2-0212 and POB “Technologie Materialowe” of Warsaw University of Technology within the Excellence Initiative: Research University (IDUB) program.

![](https://assets.underline.io/uploads/markdown_image/1/image/4e2d2b38f53f80505a1d801ab989ac98.jpg)

Fig. 1. Scanning electron micrograph of Ni2MnGa powder.

![](https://assets.underline.io/uploads/markdown_image/1/image/50cf44b9c97b07a7d8704c2818ad4355.jpg)

Fig. 2. (a) DSC results of Heusler powder and (b) TGA curves of raw PLA and PLA-based composite filaments.

Magnetocaloric Heusler Alloy Composites for Fused Deposition Modeling

High-entropy alloys (HEAs), whose new alloy design concept with multiple principal elements, attracted a lot of attention for structural application and functional aspects. Since their first report in 2004, their compositions have developed from first generation with quinary equiatomic single-phase to second-generation multi-phase structure with non-equiatomic compositions. For magnetocaloric HEAs, their limitations have been recently found to be overcome by using non-equiatomic HEA compositions: GdTbCoAlFe (with Curie temperatures up to 108 K) overcomes the low temperature limit of the rare-earth-containing HEAs (typically saturates around &lt; 60 K) [1,2] and the first-order magnetostructural phase transition in FeMnNiGeSi surpasses the smeared out magnetocaloric effect (MCE) of rare-earth-free HEAs [3,4]. In this work, we further enhance the MCE of non-equiatomic Gd34.9Tb19.4Co19Al23.3Fe3 HEA through microstructural control, in which the alloy microwires are annealed using the current density annealing technique. Induced nanocrystals in the amorphous matrix observed from transmission electron microscopy (TEM) are found to increase and grow with the current density magnitude (Fig. 1). This leads to an increase in the working temperature span of the HEA microwires and at the same time offers a relative cooling power (RCP) comparable to many reported amorphous MCE alloys, both conventional alloys and HEAs (Fig. 2). Our findings pave a pathway for further optimizing MCE through appropriate processing methods on top of careful alloy design selection.

![](https://assets.underline.io/uploads/markdown_image/1/image/fce97f9433fab8f05b035a2bf2ea02e2.jpg)

Fig. 1 TEM results of the (a) as-cast and annealed Gd34.9Tb19.4Co19Al23.3Fe3 microwires using current density values of (b) 50 and (c) 100 x 106 A m-2.

![](https://assets.underline.io/uploads/markdown_image/1/image/a7e0bd8f7ddc93b92bbc79c9201b5616.jpg)

Fig. 2 Literature comparison of RCP as a function of full-width at half maximum (FWHM) for studied microwires (star symbols) versus amorphous conventional alloys (triangles) and HEAs (squares).

Enhanced Magnetocaloric Response of High-Entropy Alloy Microwires due to Induced Nanocrystals by Current Annealing

The frequencies and wave vectors of dipolar dominated spin waves (SW) and surface acoustic waves (SAW) cover the same ranges. Therefore, the propagating waves of both kinds can potentially scatter each other - in other words, the necessary condition for the interaction in a linear regime can be satisfied. The simplest structure in which the magnetoelastic coupling between SW and SAW can be observed is the magnetostrictive layer deposited on the substrate. The confinement of SWs in the magnetic layer is necessary to induce the dipolar interaction and surface localization of SAW ensures the co-existence of both kinds of waves in the magnetostrictive layer deposited on the surface. The strength of the magnetoelastic interaction depends on the orientation of the wave vector concerning the direction of the static magnetic field[1]. Moreover, this interaction is different for different types of SAWs, specifically, Rayleigh-SAWs (R-SAW) and Love-SAWs (L-SAW)[1,4] – see Fig.1. Thus, the coupling is strongly anisotropic and cannot be observed for arbitrary selected SAWs and SWs, even if their frequencies and wave vectors match. This effect is well-known and broadly discussed in the literature[1]. Our study shows an additional factor limiting the interaction between SAWs and SWs. The SAW/SW coupling proves to require an appropriate profile of the elastic wave near the surface of the magnetostrictive structure, at distances much smaller than the wavelength. For R-SAWs the tangential component of displacement ux can have nodes within the magnetic layer, resulting in a reduction of the net strength of magnetoelastic interaction even if the strain εxx is locally significant. In an L-SAW the displacement uy does not have any nodes (uy changes monotonously in the normal direction). We have shown that this additional factor plays a role for some types of surface acoustic waves (R-SAWs), while other types (L-SAWs) are insensitive to it. We think that the studies on magnon-phonon interaction in confined geometries (surfaces, cavities) are very promising and can reveal unusual interaction mechanisms. Sample We studied [Co20Fe60B20/Au]20 multilayer of the thickness 60 nm as a magnetostrictive medium. In Co20Fe60B20 layers (2.1 nm) the magnetization is oriented in-plane and the presence of Au layers (0.9 nm) reduces the SWs’ frequencies due to out-of-plane anisotropy. The multilayer was deposited on top of a 4 nm titanium (Ti) and a 15 nm gold (Au), which buffers the naturally oxidized (001) silicon substrate. Method We measured the dispersion relations of thermally excited SAWs and magnetostatic SWs using a six-pass tandem Brillouin spectrometer (Scientific Instrumentsc©TFP2-HC), which ensures a contrast of 1015. A frequency-stabilized diode-pumped solid-state laser (Coherentc©VERDI V5) operating at λ0= 532 nm was used as a source of incident light. The measurements were performed in the 180o backscattering geometry with crossed (p-s)polarization of the incident and scattered light for SWs and non-crossed (p-p) polarization for SAWs. Using the finite element method in COMSOL Multiphysics©, we solve numerically the coupled equations of motion for magnetization and mechanic displacement. Acknowledgement The authors hereby acknowledge the financial support from the National Science Centre, Poland, project No. UMO-2016/21/B/ST3/00452. S. Mies. would like to additionally acknowledge the support from the National Science Centre, Poland, project No. UMO-2020/36/T/ST3/00542.

![](https://assets.underline.io/uploads/markdown_image/1/image/0d5d93d1592e64189ced2b9a3d060b55.jpg)

Fig.1 (left) - the illustration of the Rayleigh and Love surface acoustic waves (R SAW and L SAW). (right) -the numerically calculated profiles of the strain tensor playing the most significant role for magnetoelastic interaction of spin waves with R SAW (magnetic field applied the 45 deg) and L SAW (magnetic field applied at 0 deg). Please note that the interaction with R SAW can be canceled due to the nodal line.

Conditions for effective coupling between surface acoustic waves and spin waves

Magnetorheological elastomers (MREs) constitute ideal candidates for enabling magnetic control and reconfigurability of soft, integrated interfaces, such as valves for microfluidics, tactile displays for haptics, or actuators for flexible electronics or robotics [1-2]. MREs are composite materials made of a soft elastomeric matrix and magnetic micro- or nanoparticles. Just a few studies have focused on the actuation of MREs, which can undergo very large and rapid deformations upon application of magnetic fields [3–5]. Additionally, prior studies primarily fabricated MREs utilizing relatively large particles with sizes on the micron scale [2–8], which prevent these materials from being utilized to recreate shapes requiring sharp film curvatures in small spaces. We fabricated films with isotropic and anisotropic particle arrangements with different compositions. Anisotropic films present a steeper magnetization curve with larger remanent magnetization than their isotropic counterparts (Fig. 1a). Also, the stiffness of the films increases at a faster rate than the magnetization as a function of nanoparticle content (Fig. 1b). Therefore, for concentrations larger than 6 vol%, even if a film contains more nanoparticles (determining a larger actuation force), the film will not be able to stretch significantly more due to its stiffer nature (Fig. 2). Our isotropic films exhibit drastically higher deflections compared to other studies [3–5], up to 17x the deflections reported in Marchi et al. [5]. Our optimal film is able to deform up to 734 μm upon application of ∼100 mT, and up to 1.59 mm at ∼290 mT (the highest field measured). Finally, we implemented our optimized MRE films in a programmable and real-time reconfigurable tactile display for the visually impaired.

![](https://assets.underline.io/uploads/markdown_image/1/image/c391f5267c8607c19654a83f7fc51124.jpg)

Fig. 1: a) M vs H hysteresis loops for isotropic and anisotropic 6 vol% films and their cross-sectional structure imaged via cryo-SEM. b) Young’s moduli of the isotropic samples along with the respective magnetization values measured in the out-of-plane direction at an applied field of about 100 mT.

![](https://assets.underline.io/uploads/markdown_image/1/image/39e37ca67428400351c22efec8e423f5.jpg)

Fig. 2: Deflection measurements with hysteresis loops for a) isotropic, and b) anisotropic samples at different nanoparticle loadings.

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