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Graphene (Gr) is a particularly interesting material for spintronic and technological applications due to its low intrinsic spin orbit coupling and hyperfine interaction, which lead to high spin lifetimes and coherence lengths [1]. Furthermore, it is common in spintronic applications to introduce a structural isomorph to Gr, hexagonal Boron Nitride (hBN) to improve lattice matching in heterostructure engineering[2]. Specifically for spintronic and spin-caloritronic applications, a ferrimagnetic (FM) layer is often used as a magnon source. Therefore, it is important to understand the interfacial properties of FM/Gr(hBN) interfaces. Here, we explore the change in magnetic anisotropy in the FM insulator Nickel Ferrite (NFO) due to the inclusion of monolayer Gr and hBN. This was done by performing radio frequency transverse susceptibility measurements utilizing a tunnel diode oscillator technique, which is a sensitive probe of the system’s effective anisotropy[3]. Specifically, in-plane (IP) and out-of-plane (OOP) measurements were taken for bare NFO, NFO/Gr, NFO/hBN samples. We find that the inclusion of the Gr layer reduces the overall anisotropy for both IP and OOP drastically, by a factor of 2, in the entire temperature of 20 – 300 K. On the other hand, the inclusion of the hBN layer slightly reduces the in-plane anisotropy at low temperature (T &amp;lt; 180 K) but increases it at high temperature (T &amp;gt; 180 K). Since NFO is an insulator and Gr is a semimetal there is a large conductivity difference at the interface which likely leads to charge transfer reducing the overall anisotropy[4]. This is further supported by the less drastic change with the inclusion of monolayer hBN, a semiconductor. Relative to NFO, magnetometry measurements show an enhancement of the saturation magnetization in NFO/Gr and NFO/hBN, highlighting an additional role played by the magnetic proximity effect.

2022 Joint MMM-INTERMAG

Proximity and Charge-Transfer Mediated Magnetism at Nickel Ferrite Interfaces with Graphene and Hexagonal Boron Nitride Monolayers

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.

Graphene (Gr) is a particularly interesting material for spintronic and technological applications due to its low intrinsic spin orbit coupling and hyperfine interaction, which lead to high spin lifetimes and coherence lengths [1]. Furthermore, it is common in spintronic applications to introduce a structural isomorph to Gr, hexagonal Boron Nitride (hBN) to improve lattice matching in heterostructure engineering[2]. Specifically for spintronic and spin-caloritronic applications, a ferrimagnetic (FM) layer is often used as a magnon source. Therefore, it is important to understand the interfacial properties of FM/Gr(hBN) interfaces. Here, we explore the change in magnetic anisotropy in the FM insulator Nickel Ferrite (NFO) due to the inclusion of monolayer Gr and hBN. This was done by performing radio frequency transverse susceptibility measurements utilizing a tunnel diode oscillator technique, which is a sensitive probe of the system’s effective anisotropy[3]. Specifically, in-plane (IP) and out-of-plane (OOP) measurements were taken for bare NFO, NFO/Gr, NFO/hBN samples. We find that the inclusion of the Gr layer reduces the overall anisotropy for both IP and OOP drastically, by a factor of 2, in the entire temperature of 20 – 300 K. On the other hand, the inclusion of the hBN layer slightly reduces the in-plane anisotropy at low temperature (T &lt; 180 K) but increases it at high temperature (T &gt; 180 K). Since NFO is an insulator and Gr is a semimetal there is a large conductivity difference at the interface which likely leads to charge transfer reducing the overall anisotropy[4]. This is further supported by the less drastic change with the inclusion of monolayer hBN, a semiconductor. Relative to NFO, magnetometry measurements show an enhancement of the saturation magnetization in NFO/Gr and NFO/hBN, highlighting an additional role played by the magnetic proximity effect.

poster

We investigate magnetic, thermal, and magnetocaloric properties of rare earth intermetallic compounds with 0.25, 0.5 and 0.75, through a theoretical model Hamiltonian that considers contributions of the crystalline electric field anisotropy in both Tm and Dy magnetic sublattices, disorder in exchange interactions among Tm-Tm, Dy-Dy and Tm-Dy magnetic ions, and the Zeeman effect. Employing earlier reported [1] and new experimental measurements, we first determine a single free variable, the intersublattice magnetic exchange parameter, to properly model the temperature and magnetic field dependencies of heat capacity and magnetization. Then we used the modeling results to explain the emergence of an anomalous spin reorientation transition and its influence on the magnetocaloric effect in the title compounds. Theoretical results agree with experimental data reasonably well.

Magnetic and magnetocaloric properties of TmxDy1-xAl2 (x = 0.25, 0.50 and 0.75)

Multi-component alloys contain more than 4 elements in percentages between 12 to 35%, this can lead to single or dual phase alloys. These dual phase alloys have been shown to have promising magnetic properties [1,2], therefore further investigation is required. Two studies were carried out on the CoFeNi0.5AlCrx alloy to investigate how the structural and magnetic properties change as a function of Cr concentration and post-synthesis heat treatment. The addition of Cr to CoFeNi0.5Al changed the alloy from single phase BCC to dual phase BCC, due to the formation of nanoparticles within a matrix (Fig 1a). The Cr also reduced the saturation magnetisation at 300K. The dual phases gave rise to 2 different magnetic phases: i. high Curie temperature (Tc) almost independent of Cr, ii. low Tc decreasing with increasing Cr (Fig 1b). For CoFeNi0.5Cr0.5Al, four post heat treatments were investigated, these were either heated at 1423K for 5 or 10hrs, then either furnace cooled or water quenched. All the samples were BCC, with the water quenched 10hrs (WQ10) and furnace cooled 5 and 10hrs (FC5 and FC10) alloys all having nanoparticles within a matrix, while the water quenched 5hrs (WQ5) alloy had no clear separation of phases. These differences were observed in the Tc, as for WQ10, FC5 and FC10 alloys there were 2 distinct transition in the M-T curves (Fig 1c), while for WQ5 the transition appear as one broad change. The magnetocaloric properties were studied for all the CoFeNi0.5AlCrx alloys. It was found that Cr decreased the change in entropy (ΔS) for both Tc (Fig 1d). For all alloys, the low Tc had a smaller ΔS compared to the high Tc but a larger refrigerant capacity due to a wider temperature transition. For CoFeNi0.5AlCr0.25, the two Tc were within 100K of each other, such that the ΔS curves overlapped giving a wider temperature range, and a refrigerant capacity of 150J/K. Thus tuning the two transitions to be &lt;100K of each other increases the refrigerant capacity.

![](https://assets.underline.io/uploads/markdown_image/1/image/585620410c5d908d21de5098c3a453fc.jpg)


Figure 1a. SEM images of CoFeNi0.5AlCrx, Magnetisation as a function of temperature at 20 kA/m for 1b. CoFeNi0.5AlCrx and 1c. CoFeNi0.5AlCr0.5 and 1d. Change in entropy as a function of Cr concentration (open shapes = low Tc, and solid shapes = high Tc)

Investigating the structural and magnetic properties of CoFeNi0.5AlCrx

Pressure sensor (PS) has important application in artificial intelligence and modern industries. Baromagnetic effect (BME), i.e., pressure-induced magnetic moment change, is regarded as the candidate technology for new PS. The reported large BME in Mn3Ga0.95N0.94[1] has gained great attention. The origin comes from the pressure-induced spin re-orientation from Γ5g antiferromagnetic (AFM) to M-1 ferrimagnetic phase. Recently, the ternary metallic compounds MM’X (M, M’ = transition metals, X = main elements) have attracted renewed attention due to their barocaloric effect[2], and giant negative thermal expansion[3]. In the MM’X family, previous research indicated that the AFM coupling of the stoichiometric MnNiGe is very robust. The substitution of Mn with Fe introduces Fe-Mn ferromagnetic (FM) coupling, which can help to establish a cone-spiral magnetic coupling[4]. Hence, a new cycloidal spiral AFM structure (CyS-AFMb) was discovered in Mn0.87Fe0.13NiGe[5], which is sensitive to magnetic field and stress. As a result, a giant BME was achieved. The employed Mn0.87Fe0.13NiGe alloy were prepared by arc-melting technique. The CyS-AFMb was discovered in Mn0.87Fe0.13NiGe below 150 K. A low magnetic field can make the CyS-AFMb transform to a conical spiral FM with angle 70°(70°-CoS-FMb), accompanied by a step rise of magnetization (Fig.1). More importantly, the new CyS-AFMb is no longer insensitive to stress compared to the MnNiGe without Fe-doping. A pressure higher than 4kbar induces abnormal change of Mn(Fe)-Mn(Fe) distances hence transform the CyS-AFMb into a conical spiral ferromagnetic configuration(45°-CoS-FMa) with easily magnetized but much shortened magnetic moment (Fig.2). As a result, giant BME was observed under either a low magnetic field or a field of 2T~5T. The maximal BMC appears to be ~5.34 emu/g*kbar under 0.35T while ~9.03emu/g*kbar under 2.2T in a wide temperature range, which all far exceed those of the previous reported Mn3Ga0.95N0.94.

![](https://assets.underline.io/uploads/markdown_image/1/image/09482e36daa9f397642695bac745587e.jpg)

Fig.1. a)M-H curve at 5K with the sketch of spin structure evolution with H, b)Variable magnetic field NPD patterns at 5K, and c)phase diagram.

![](https://assets.underline.io/uploads/markdown_image/1/image/40c700b274a5a459169e05205fd24437.jpg)

Fig.2. The sketch of a)the CyS-AFMb andb)the 45°-CoS-FMa, and the variable pressure NPD patterns at 120K.

A new spin structure and giant baromagnetic effect in Mn0.87Fe0.13NiGe alloy

Magnetostrictive materials represented by Terfenol-D, Galfenol and Fe-Co have the advantages of high energy density, fast response speed, control accuracy and high displacement resolution，and have been widely used in the fields of precision machining, ultrasonic cleaning, actuator. Under the condition of high frequency excitation, there are more hysteresis loss, eddy current loss, copper loss of excitation winding in the magnetostrictive device. The existence of various losses will change the temperature value and distribution of the material. Due to the temperature-sensitive properties, the material exhibits different magnetic and mechanical properties at different temperatures. If only the magnetic properties at room temperature are used to analyze the various performance of the magnetostrictive device in actual work, the analysis results will appear large deviations from the actual phenomenon. Therefore, it is necessary to accurately analyze the magnetic properties of magnetostrictive materials at different temperatures. Reference [1] tested the high frequency characteristics of Terfenol-D and improved the traditional loss separation formula based on the loss test data. Reference [2] measured and analyzed the magnetic and loss characteristics of ferrite, nanocrystal and amorphous alloy. On this basis, a temperature-controllable high-frequency magnetic characteristic test system is built based on the AMH-1M-S dynamic magnetic characteristic tester and a thermostat. The high-frequency magnetic properties of Terfenol-D, Galfenol and Fe-Co at different temperatures (10-80°C) were measured, and a comparative analysis was made from the magnetic domain rotation and mechanism. The results show that the three samples have the same change trend affected by temperature, but the degree of change is obviously different. Among them, Terfenol-D has the strongest temperature sensitivity and the largest magnetic energy loss. Figure 1 shows the hysteresis loops of the three materials. Figure 2 shows the loss trend of the three samples at different temperatures.

![](https://assets.underline.io/uploads/markdown_image/1/image/c3f4432877943ab0f51f966dc12fd20f.jpg)

Fig.1. The hysteresis loop of three materials (f=10 kHz, Bm=0.06 T, ΔT= 20°C)

![](https://assets.underline.io/uploads/markdown_image/1/image/86d282f7234c7040115fc5cb5a072288.jpg)

Fig.2. The loss trends of three materials at different temperatures (f=10 kHz, Bm=0.06 T)

Analysis and Experimental Research on High Frequency Magnetic Properties of Different Magnetostrictive Materials Considering Temperature Effect

Eu2In was recently reported to exhibit a giant nonhysteretic magnetocaloric effect due to a first-order magnetic phase transition with a small phase volume change of approximately 0.1% around TC = 55 K [1]. We present magnetic and compute magnetocaloric properties of a Eu2In compound using a microscopic description based on a model Hamiltonian that takes into account magnetic exchange and magnetoelastic interactions [2]. In the model the thermodynamic nature of the transition is conveniently represented by a single magnetoelastic interaction parameter. A good agreement between the theoretical results and earlier published experimental data confirms the effectiveness of our approach. Keywords: Hysteresis; magnetocaloric effect; intermetallic compounds; magnetoelastic.

Theoretical investigation of the nonhysteretic first-order phase transition of Eu2In through free-energy analysis

Hybrid magneto-elasto-optical systems have the potential to translate surface strain into a color change for structural health monitoring (SHM), mediated by the magnetic coupling between two different functional materials, specifically magnetostrictive and magnetochromatic materials. This hybrid system has the potential to be applied as a paint to large structures, therefore small particle sizes are needed to allow the particles to stay suspended in solution. In this work, polymer-matrix composites with magnetostrictive Fe-Al alloy particles are evaluated to determine the magneto-elastic coupling properties in composite patches attached to a surface prior to understanding the hybrid magneto-elasto-optical interaction. Fe-Ga alloy (Galfenol) powders are usually considered for use in magnetorheological (MR) fluids, MR elastomers for tactile sensors, and SHM systems as composite patches to detect ultrasonic guided waves [1-5]. Figure 1 shows changes of magnetic properties as functions of Alfenol particle fraction and shape, associated with the magneto-elastic coupling effect under compressive stress along the out-of-plane direction. A tension apparatus was also designed to control applied stress precisely to the composite patches attached on dog-bone specimens in a solenoid coil. Flake-shaped particles are more sensitive to increases in applied stress than spherical particles. In addition to the static state, Alfenol MPCs with flake-type powders exhibited better sensing performance than Galfenol ones at frequencies of 120 kHz using ultrasonic guided wave techniques.

![](https://assets.underline.io/uploads/markdown_image/1/image/cecc9dc45f21565956e9a9cefcde1ca7.jpg)

Figure 1. Magnetic properties of composites and particle images; (a)-(b) magnetization and initial permeability as functions of particle shape and weight fraction, where average particle size in diameter was 80 μm and magnetic field was applied out of the plane of the composite patch during curing, (c) permeability changes as a function of compressive stress using a clamping shaft collar to squeeze disc patch on a vertical VSM sample holder, and (d) SEM images of flake and spherical type Alfenol powders with a size of 106-150 μm in diameter, where flake powders were prepared from gas-atomized powders using a wet ball milling process

Static and dynamic magneto-elastic sensing properties of Fe-Al alloy powder-epoxy composite patches

In this work, an investigation of the effect of magnetic particles with different aspect ratios on the effective magnetization response of magnetorheological elastomers (MREs) was carried out. MREs are composites that consist of magnetically permeable particles dispersed in a nonmagnetic polymeric matrix [1]. These materials are well known due to their tunability property. When subjected to an externally applied magnetic field, changes occur in their mechanical properties leading to the so-called magnetorheological (MR) effect [2]. This is often attributed to the magnetic interaction among the magnetic filler particles [3]. Several factors significantly influence the MR effect such as the polymer matrix, particles-volume fraction, size, and shape of the magnetic particles [4]. In this study, based on continuum formulation theory, microscale modeling using a finite element analysis (FEA) was used to determine the effect of the latter on the macroscopic magnetization of MREs. Using Jiles-Atherton hysteresis model parameters, the hysteresis loops of MRE were numerically resolved in the FEA software, COMSOL Multiphysics [5]. The simulations were performed for randomly oriented (unaligned) and aligned microstructures with a constant particle-volume fraction (φ= ~20%) and varying particle-aspect ratios (AR=1, 2.5, 5, and 7.5). A computational homogenization scheme is used to relate the microscopic behavior to the macroscopic properties of these composites. From the analysis, it was found that for unaligned MRE the effective magnetization increased with an increase in the particle-aspect ratio particularly in the linear region, the saturation magnetization is seen to be independent of the particle shape (see Fig. 1a). This effect is much more noticeable for particles aligned with the applied field (see Fig. 1b). While for particles aligned perpendicular to the applied field, an opposite effect is seen where increasing aspect ratio resulted in decreasing of magnetization relative to the applied field.

![](https://assets.underline.io/uploads/markdown_image/1/image/673dfe975f4e9f5f93d9f4391801799d.jpg)

Effective magnetization behavior for a) unaligned MRE with varying particle-aspect ratios

![](https://assets.underline.io/uploads/markdown_image/1/image/51957b3197e5d077bdeb8f450137abdd.jpg)

Effective magnetization behavior for b) aligned MRE with different particle-aspect ratios

Study of Effective Particle Shape-Dependent Magnetization Behavior of Soft Magnetic Polymeric Composites

In recent years, various methods have been reported to boost the magneto-optical (MO) response. Several works have reported the enhancements of the MO response relying on the plasmonic effects attributed to the strongly confined electromagnetic field in the structures1-3. However, the nonnegligible disadvantage of this approach is the optical losses due to the high absorption coefficient of the metal materials1. Therefore, combining the all-dielectric metasurfaces which have high-refractive-index and low intrinsic loss with planar photonic structures offers an alternative route to these problems4,5 .But most of the observations so far are focused on enhancement of existing magneto-optical effects in planar MO thin films. A high index contrast, all dielectric magneto-optical metasurface featuring strong Mie resonance modes have not been fabricated. Here, we report observation of circular displacement current induced novel magneto-optical effects in a high index contrast Si/Ce:YIG/YIG/SiO2 all dielectric metasurface. We observe giant transverse magneto-optical Kerr effect (TMOKE) up to 7 % under s-polarized incidence, which is non-existent in planar magneto-optical thin films. This phenomenon is essentially originated from the unique circular displacement current when exciting the magnetic resonance modes, which changes the incident electric field direction locally. These results indicate promising potential of controlling light propagation by utilizing the complex Mie resonance modes in magneto-optical all dielectric metasurfaces. Our work may inspire the development of novel magneto-nanophotonic devices such as vectoral magnetic field sensing, free space non-reciprocal photonic devices and magneto-optical imaging.

![](https://assets.underline.io/uploads/markdown_image/1/image/d3d7bd3c840418fd37285dae4d310845.jpg)

Figure 1. (a) Schematic diagram of the metasurface. (b) Scanning electron microscope image of a fabricated device.

![](https://assets.underline.io/uploads/markdown_image/1/image/22950e3df3d860eae0c79b53767f7e8a.jpg)

Figure 2. (a) Schematic diagram of s-polarized TMOKE characterization set-up. (b)Measured s-polarized TMOKE and reflection spectra of the metasurface compared with bare Ce:YIG/YIG thin films. (c) Measured TMOKE hysteresis for the metasurface and the bare MO films at 1230 nm wavelength. (d) Simulated reflection spectra and TMOKE responses of the metasurface for s-polarized light.

Circular Displacement Current induced Novel Magneto-Optical Effects in All-dielectric Metasurfaces

Recently, the range of applications of magnetic emulsions has significantly expanded due to the development of microfluidics [1] and biomedical technologies [2]. Using magnetically sensitive emulsions, methods have been proposed for measuring the viscosity and surface tension of liquids [3] and even for determining the content of methyl alcohol [4]. In this work, we present the results of a study of the effect of diffraction scattering of light in magnetic emulsions with low interfacial tension, synthesized based on AMG-10 hydraulic oil. Magnetic emulsions were produced by mixing kerosene-based magnetic fluid in AMG-10 hydraulic oil. The size of microdroplets could vary from 1000 to 7000 nm. To study the effect of diffraction scattering of light, an optical setup was used, which consisted of a helium-neon laser with a radiation wavelength of 633 nm, a cylindrical cuvette, and a screen. The image of the diffraction pattern was recorded by the CMOS matrix of a camera. Image processing was performed using specialized software ImageJ. The sample cuvette was a glass cylinder, fixed on a fluoroplastic tube driven by a DC motor with a belt drive. The range of rotation frequencies was 9–200 rpm. The diffraction pattern is oriented in the direction perpendicular to the long axes of the elongated microdroplets. When the cell is rotated, the droplet axes deviate from the direction of the magnetic field along the direction of rotation, which leads to a rotation of the diffraction band relative to the initial direction. The deflection angle depends on the cell rotation speed and the magnetic field strength (Fig. 1 and Fig. 2). The interpretation of the effect of diffraction scattering in magnetic emulsions is based on considering the diffraction of light by an irregular structure of elongated microdroplets of various sizes, located randomly. Calculations give a result that is in complete agreement with the experiment. This work was financially supported by the Ministry of Science and Higher Education of Russia (project no. 0795-2020-007).

![](https://assets.underline.io/uploads/markdown_image/1/image/e6e5e813cc0937954adfe430afa77353.jpg)

Photographs of the diffraction pattern at the various magnetic fields and rotation speeds

![](https://assets.underline.io/uploads/markdown_image/1/image/d097e27fe9c0f03ed59cd09cccf39265.jpg)

Dependence of the angle of rotation on the rotation speed (magnetic field is H=2 kA/m)

Light diffraction in rotating magnetic emulsions in a magnetic field

Iron-based garnet films that have large magneto-optical (MO) effect are a promising material for MO device applications. In particular, terbium iron garnet (TbIG) can crystallize directly on a Si substrate without garnet seed layers [1-4] and, therefore, recent investigations show quite practical optical isolators taking advantage of TbIG [1,2]. However, crystallization for TbIG requires high temperatures and it is desirable to limit the heating to those regions of the chip where devices are formed. In this study, we compare the structure, magnetic and MO properties of TbIG and Bi doped TbIG (Bi-TbIG) films processed by rapid thermal annealing (RTA) to those annealed locally using an embedded resistor with 40-μm-square area. TbIG (Tb2.77Fe5O12) and Bi-TbIG (Bi0.02Tb2.82Fe5O12) films are made by pulsed laser deposition at room temperature, which allows for liftoff patterning using a photoresist mask. The crystal structure for the films is characterized by micro-Raman spectroscopy and X-ray diffraction (XRD) and the magnetic properties by vibrating sample magnetometry. XRD shows single phase garnet after RTA 1073 – 1273 K. Raman spectra for Bi-TbIG film before/after 1173 K annealing and for the Si substrate are shown in Fig. 1. The Raman spectrum for the as deposited film is almost the same as that of the Si substrate while a Raman peak corresponding to the strongest peak of TbIG (Eg) is observed around 261 cm-1 in the annealed film. Raman spectroscopy enables detection of local crystallization in Bi-TbIG on embedded resistors. Figure 2 shows room temperature in-plane M-H loops of the annealed TbIG and Bi-TbIG films. The TbIG film is not saturated at 1 T while the Bi-TbIG is saturated at 0.7 T. Coercivity in TbIG rapidly increases in the vicinity of the compensation temperature (Tcomp) [3] which is ~250 K for bulk TbIG, and slightly lower for thin film TbIG with Tb deficiency [4]. Bi doping lowers (Tcomp) further [4] explaining the easier saturation of the Bi-TbIG film. The high figure of merit of Bi-TbIG and its higher remanence make this material attractive for integrated photonic devices.

![](https://assets.underline.io/uploads/markdown_image/1/image/db285f5491540908bdd48574e79691ed.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/ff4aa0a91ef334bb9894df68b9074960.jpg)

Proximity and Charge-Transfer Mediated Magnetism at Nickel Ferrite Interfaces with Graphene and Hexagonal Boron Nitride Monolayers

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Magnetic and magnetocaloric properties of TmxDy1-xAl2 (x = 0.25, 0.50 and 0.75)

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