United States

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

2022 Joint MMM-INTERMAG

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

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.

poster

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

Rare-earth chromite DyCrO3: Structural and magnetic properties

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.

Peculiar magnetic phase transition and large magnetocaloric effect in Nd2In

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

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

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