United States

High-entropy alloys (HEAs), instead of employing one or two main constituents like in traditional alloy development, adopt a different design concept where it combines a blend of multi-principal elements in large concentrations. This design idea enables them with large values of configurational entropy of mixing and a vast compositional space which offers a huge window of exploration opportunities.&lt;br/&gt;&lt;br/&gt;Magnetocaloric HEAs have been limited to low-temperature range or showing sub-par performance till recent extensions to the first-generation equiatomic HEA design approach have been devised [1, 2]. The magnetocaloric performance of equiatomic magnetocaloric HEAs heavily depends on the choice of element selection and thus the likelihood of relying on the rare-earth (RE) elements due to their intrinsic large magnetic moments. Extending beyond the equiatomic point towards non-equiatomic in the HEA region combined with directed search strategies, overcomes the above-mentioned limitations of magnetocaloric HEAs: the low temperature limit is improved (48 % increase as displayed in Fig 1) and â‰¥ 5-fold performance enhancement (Fig 2) [3-5]. In this talk, we will show the various design strategies of magnetocaloric HEAs and how to tackle the vast HEA space to tune for the desired magnetocaloric properties.&lt;br/&gt;&lt;br/&gt;Work supported by Grant PID2019-105720RB-I00 funded by MCIN/AEI/ 10.13039/501100011033. Additional support ConsejerÃ­a de EconomÃ­a, Conocimiento, Empresas y Universidad de la Junta de AndalucÃ­a (grant P18-RT-746), US Air Force Office of Scientific Research (FA8655-21-1-7044) and Sevilla University under VI PPIT-US program.

MMM 2022

Tuning in the vast high entropy alloy space for competitive magnetocaloric properties

High-entropy alloys (HEAs), instead of employing one or two main constituents like in traditional alloy development, adopt a different design concept where it combines a blend of multi-principal elements in large concentrations. This design idea enables them with large values of configurational entropy of mixing and a vast compositional space which offers a huge window of exploration opportunities. Magnetocaloric HEAs have been limited to low-temperature range or showing sub-par performance till recent extensions to the first-generation equiatomic HEA design approach have been devised [1, 2]. The magnetocaloric performance of equiatomic magnetocaloric HEAs heavily depends on the choice of element selection and thus the likelihood of relying on the rare-earth (RE) elements due to their intrinsic large magnetic moments. Extending beyond the equiatomic point towards non-equiatomic in the HEA region combined with directed search strategies, overcomes the above-mentioned limitations of magnetocaloric HEAs: the low temperature limit is improved (48 % increase as displayed in Fig 1) and â‰¥ 5-fold performance enhancement (Fig 2) [3-5]. In this talk, we will show the various design strategies of magnetocaloric HEAs and how to tackle the vast HEA space to tune for the desired magnetocaloric properties. Work supported by Grant PID2019-105720RB-I00 funded by MCIN/AEI/ 10.13039/501100011033. Additional support ConsejerÃ­a de EconomÃ­a, Conocimiento, Empresas y Universidad de la Junta de AndalucÃ­a (grant P18-RT-746), US Air Force Office of Scientific Research (FA8655-21-1-7044) and Sevilla University under VI PPIT-US program.

technical paper

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

MMM 2022 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 tutorial, and several special sessions. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

<iframe width="560" height="315" src="https://s3.amazonaws.com/pf-user-files-01/u-59356/uploads/2022-11-02/un13zp7/MMM%20Welcome%20Video%20v5.mp4" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

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

Please register for the MMM 2022 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.

Magnetic elastomers are flexible smart materials that can be manipulated by magnetic fields to achieve reversible mechanical deformation. These highly configurable materials are instrumental in transforming biomedical applications such as artificial muscles, dampeners, and other vibration absorbers. Magnetic elastomer structures must be customizable to satisfy these complex applications leading to the use of fused filament fabrication (FFF) in creating them. FFF is a 3D printing process where material is extruded in 1D lines (infill) to build 2D planes layer-by-layer, resulting in a 3D structure. This research used magnetoactive testing to investigate how varying the internal infill structure affected the mechanical response of the structures within an applied magnetic field. Different infill percentages and infill orientations were tested to account for different mechanical stiffnesses and internal geometries. The elastomers were made by adding 40wt% magnetite (Fe3O4) to a thermoplastic polyurethane (TPU) matrix. Each sample was magnetoactively tested with three different transverse magnetic field orientations (Front, Back and Top). The samples were placed between two electromagnets, and the angle of deflection was recorded as a function of applied field. Maximum angles of deflection for the testing setup were reached when both lower infill percentages, translating to less material in the cross-section of the sample, and lower infill orientations, creating much less crosslinking between infill lines, were used. Transverse fields applied parallel to the print plane (Front, Back sample orientations) demonstrated the most magnetoaction due to less crosslinking constraining the bending stiffness. The anisotropy of the infill structure likely also contributed to the large response from certain samples. It was concluded that for this fixed base material, it is more important to 3D print structures with lower stiffnesses than more net magnetic particulate in achieving the most magnetoaction. According to this data, 3D printed magnetite-TPU structures are viable for creating components easily stimulated by a magnetic field unlocking many possibilities for the creation of useful technological components.

Magnetoactive Properties of 3D Printed Magnetic Elastomer Structures: Effects of Infill Orientation and Infill Percentage

Magnetic elastomers are composite smart materials made up of a flexible polymer and magnetic particulate which mechanically actuate in response to an applied magnetic field (H). They allow for a highly configurable and untethered actuator. To enhance configurability, 3D-Printing allows for great control of the objects meso and macro structure, both in terms of shape geometry and property anisotropy. Specifically, Fused Filament Fabrication (FFF) is a process by which material is extruded in lines (infill) to gradually build up an object through layer-by-layer extrusion. In this study, we explore how multiple FFF structural parameters (infill orientation and infill percentage, and sample orientation relative to H) affect the magnetoactive response of printed Strontium Ferrite (SrF) magnetic elastomer structures. Magnetic elastomers with hard magnetic particulate have the unique advantage of performing more complex actuation, such as rolling, twisting and folding. SrF is an excellent hard magnet candidate given its lower price and greater accessibility compared to NdFeB. Magnetoactive properties are measured by a custom setup where each printed sample beam is suspended and optically tracked for a transverse H up to 0.4 T. For each sample, multiple orientations relative to H are studied. A custom program overlays the digital images for increasing H in order to quantify the magnetoactive deformation that results. The magnetoactive responses exhibited by the various sample types highlight clear design goals for tailoring large and complex magnetoactive actuation modes. In addition to the traditional transverse bending seen from typical (soft) magnetic elastomers, we also observe complex twisting and torquing of the beams in multiple dimensions based upon the printed structure and the sample orientation relative to H. These effects are greatest for the orientations and structures that maximize magnetic anisotropy and minimize the infill crosslinking. This work demonstrates the clear potential to tailor complex magnetoactive responses from FFF-printed hard magnetic elastomers, opening the door to highly complex actuators that can be readily and accessibly designed and created.

Complex Magnetoactuation of 3D Printed Hard Magnetic Elastomers: Effects of Infill Orientation and Percentage

Magnetic elastomers can mechanically deform under a magnetic field. Hard magnetic elastomers can perform more complex motions, but soft magnetic elastomers have a greater magnetoaction. 3D printing, such as Fused Deposition Modeling (FDM), can enhance the magnetoactive properties of magnetic elastomers by creating anisotropy. 3D printing filaments are the stock material for FDM. Recent work has shown that magnetic annealing of magnetic filaments during extrusion creates greater magnetoaction in the filaments. This research studies whether this enhanced performance from magnetically annealed filaments remains once they are extruded through the 3D printing nozzle. The composite samples were made of polyurethane and varying amounts of soft and hard magnetic particulate (carbonyl iron (Fe) and strontium ferrite (SrF)). The composites were extruded into 1.75 mm diameter filaments. Magnetically annealed filaments traveled through a uniform axial magnetic field. Final samples were extruded through a 0.8 mm FDM nozzle into extrudates. The magnetoactive properties were measured by a custom setup, whereby extrudates were hung between electromagnets. Images of samples were captured, overlaid, and analyzed at seven field strengths. The enhanced magnetoactive performance of magnetically annealed filaments was present in the final extrudates, indicating that the magnetic annealing effects were preserved. The higher performance magnetic annealing effects were (1) magnetoaction at lower applied fields for the Fe-containing samples and (2) non-zero magnetoaction in the highest SrF samples. Quantitatively, the least magnetoactive deflection was seen in the highest SrF samples. Mechanical tensile testing data showed that the stiffness of the composite variant increased with a higher percentage of SrF. Magnetically, the samples with more SrF content had lower saturation magnetization (Ms) and higher coercive field (Hc). The high stiffness and magnetic properties contribute to the limited magnetoaction. This approach to magnetic annealing of magnetic elastomers can be used to 3D print accurate and complex components for high-performance soft robotic applications.

Impact of 3D Printing Extrusion on Magnetically Annealed High Performance Hard/Soft Magnetic Elastomers

Considering the natural abundance of the constituting elements and first-order phase transition (FOPT), LaFe13-xSix-derived compounds have been extensively studied for magnetocaloric effect, a phenomenon that causes the cooling or heating of material when placed in an external magnetic field [1]. They are, however, extremely brittle and mechanically friable, showing rather low thermal conductivities and measurable irreversibility, which thus far could not be eliminated completely. Recently, Pathak et al. [2] reported the first-time discovery of a two-phase, naturally formed at the LaFe2Si stoichiometry rather than LaFe13-xSix compound. LaFe2Si exhibits strongly responsive behaviors without the degradation in properties that can be exploited in weak magnetic fields. However, the phase transition happens rather at low temperatures and the saturation moment is low. We are working on this material to further enhance the phase transition temperature and also to improve the magnetic and mechanical properties of the alloy. In this presentation, we will present the synthesis and characterization of LaFe2-yCoySi. We prepared LaFe2-yCoySi by making the first pre-alloy of FeCoSi and then added Co and melted several times. The alloys were further homogenized by the vacuum suction casting technique, which prepared a 4 to 5 cm long rod with a 6mm diameter of sample. The ferromagnetic to paramagnetic transition temperature increases from 199K for x = 0 to 273K for x = 0.3 and the full width at the half-maximum value of magnetic entropy changes increases significantly with Co doping. We discuss the phase transition, electrical transport, magnetic and magnetocaloric properties of LaFe2-yCoySi compounds.

Phase transition, electrical transport and magnetic entropy change of LaFe2 yCoySi alloys prepared by suction casting

The ability to harness excellent magnetic and optical properties within a heterostructure film composed of a magnetic material and a transition metal dichalcogenide (TMD) semiconductor paves a new pathway for the development of multifunctional sensing devices, information storage technology, etc1. Atomically thin tungsten disulfide (WS2) (thickness â‰¤ 5 nm) has been widely explored as a promising candidate for applications in optoelectronics, spintronics, and valleytronics. The valleytronic property of WS2 can be enhanced when interfacing it with another magnetic material such as iron (Fe), due to the magnetic proximity effect2. However, the growth of this 2D-TMD with controllable thickness, using chemical vapor deposition (CVD), and transferring it onto another substrate (Fe) via a commonly used wet transfer process have remained a challenging task. To overcome this, we employ a combination of pulsed laser deposition (PLD) and sputtering (SP) techniques to grow Fe/WS2 heterostructure films with a controlled interface and desirable magnetic/optical properties. A 5nm thick WS2 film was first grown on MgO substrate using PLD, and a 5nm thick Fe film was then deposited on WS2/MgO using SP. A 2nm thick Ta layer was sputtered on the Fe surface to protect the film from oxidization. X-ray diffraction, Raman and Photoluminescence spectroscopy, and atomic force microscopy confirmed the structure of the heterostructure and the quality of the Fe/WS2 interface. Vibrating sample magnetometry, magneto-optical Kerr effect (MOKE), and magnetic force microscopy indicated that the excellent magnetic properties of Fe are preserved in the Ta/Fe/WS2/MgO heterostructure relative to the Ta/Fe/MgO reference film. MOKE showed a sharp, square magnetic hysteresis loop of Ta/Fe/WS2/MgO with a coercive field (Hc ~ 25 Oe) similar to that of the reference film, Ta/Fe/MgO (Hc ~ 23 Oe). The combined excellent magnetic and optical properties make the Ta/Fe/WS2/MgO heterostructure a promising candidate for a wide range of applications in spintronics, valleytronics, and opto-spincaloritronics3. Our study provides a new, efficient method for the growth of novel 2D van der Waals TMD-based heterostructures with controlled interface properties.

Growth of iron/tungsten disulfide heterostructure films with controlled interface and magnetic properties

Anisotropic magnetoelastic thin films have a significant modification of the acoustic properties near spin reorientation transition (SRT)[1]. These high sensitivity and nonlinearity of the magnetic system have great potential applications in ultrasonic diagnosis and imaging, magnetic sensor and microactuation[2]. In this work, we have prepared FeCoSiB (20 nm)/NiFeCu (10-80 nm) bilayers with induced uniaxial anisotropy on Si substrate by magnetron sputtering, and investigated the magnetization dynamics using a low field ferromagnetic resonance (FMR) technique. As shown in Figure 1, the imaginary permeability spectra gradually split from single to double peaks and then to a single peak, when an opposing magnetic field is applied along the easy axis. Fig. 2 shows the variation of the resonance frequencies with the external magnetic field from -150 to 150 Oe. Although the frequency of the single resonance peak satisfies the linear relation of modified Kittel formula[3,4], the splitting of resonance peaks was not captured in previous work to the best of our knowledge. Independent on the NiFeCu thickness, this splitting always occurs at certain magnetic field near the coercivity, thus, may be attributed to spin reorientation transition (SRT)[5]. In the SRT region, the intensity of the low frequency peak decreases with the increase of the reverse magnetic field, while the intensity of the high frequency peak increases continuously, indicating that the Zeeman interaction compensates the anisotropy. Moreover, the field range of SRT region is related to the thickness of bilayer, the effective magnetization, the exchange coupling constant and the magnetoelastic constants. It is found that the FeCoSiB (20 nm)/NiFeCu (30 nm) bilayer has the maximum SRT magnetic field range, where the NiFeCu layer is expected to be near the SRT thickness. These results provide insights into the design of novel straintronic devices and the understanding of magnetization dynamics of ferromagnetic bilayers.

Ferromagnetic resonance in magnetoelastic NiFeCu/FeCoSiB bilayers near spin reorientation transition

Owing to the relative abundance of its constituent elements and large MCE observed near room temperature, the AlFe2B2 system has attracted much attention recently [1]. As an alternative to current rare earth materials, AlFe2B2 promises the realization of cleaner, energy efficient refrigeration technologies based on phenomena associated with MCE [2]. Additionally, excess Al is believed to generate phase impurities which can change the observed MCE properties of this system [3]. By dissolving certain impurities in acid, a significant enhancement of the MCE properties of this system have been observed [4]. Considering this behavior, we have studied the effect of acid treatment on the magnetic, magnetocaloric, and transport properties of Al0.85+xSi0.15Fe2B2 (x = 0.2, 0.4). The goal was to explore the possibility of enhancing the MCE properties of the materials by adding excess aluminum and subjecting them to acid treatment after annealing. The samples were prepared by arc melting followed by drop-casting. The drop-casted samples were annealed followed by acid treatment. The alloys were characterized by x-ray diffraction, scanning electron microscopy, dc magnetization, and electrical resistivity measurements. The second order ferromagnetic phase transitions were observed near room temperature (~298 K â€“ 315 K) and peak magnetic entropy changes (-Î”SM) of more than 4 J/kg K were observed for a field change of 5 T. The details of phase purity, microstructure, magnetic, and transport properties of the acid treated and the drop casted annealed materials will be presented.

The effect of acid treatment on the magnetic and magnetocaloric properties of Al rich Al0.85+xSi0.15Fe2B2

Magnetic refrigeration is an environmentally friendly cooling technology, which is believed to be significantly more efficient than the currently employed gas-compression-based cooling technologies. The commercialization of this technology is crucially dependent on the discovery of materials that exhibit large magnetocaloric effects and can be easily fabricated using cheap, non-toxic, and readily available elements. The intermetallic Mn1-xFex-Î´NiÎ´Si1-yAly compounds are known to exhibit large magnetocaloric effects at the relatively low magnetic field (H = 2T or lower) and tunable phase transition [1, 2]. These materials have gained much interest in recent years due to the fact that the constituent elements are cheap and readily available. However, selected drawbacks including large thermal hysteresis and mechanical instability make these materials unsuitable for application. More research efforts are required to eliminate these drawbacks so that the application potential for these materials can be realized. Therefore, we have synthesized the substitution of Ni with Co in Mn0.5Fe0.5Ni1-xCoxSi0.94Al0.06 (0.025 â‰¤ x â‰¤ 0.075) alloys by arc melting followed by a rapidly quenched vacuum suction casting technique and study the magnetic and magnetocaloric properties of the system, which has not been reported yet. X-ray diffraction and scanning electron microscopy (SEM) data indicated that the samples exhibited a single-phase. Peak magnetic entropy changes of (â€“ Î”SM) of as-cast alloy with x =0.025 is found to be 12 and 31 J kg-1K-1 for Î”H = 2 and 5 T, respectively around 225 K. The observed large MCEs are due to the first order magneto-structural phase transition exhibited by the materials from low-temperature ferromagnetic orthorhombic phase to high-temperature paramagnetic hexagonal phase. In this presentation, we present details of phase purity, microstructure, and magnetic properties of as-prepared and heat-treated alloys with 0.025 â‰¤ x â‰¤ 0.075

Magnetocaloric properties of Co doped Mn0.5Fe0.5Ni1

The giant magnetocaloric (MC) effect measured in Mn0.5Fe0.5NiSi1-xAlx alloys ( 0.05 Â£ x Â£ 0.07) for a low magnetic field change (|Î”SM|max ~16-24 Jkg-1K-1 at 2 T) [1], and the fact that they are based on cheap and abundant elements motivated the interest on their study. The effect is linked to their first-order martensitic-like magnetostructural transformation (MST) from a high-temperature hexagonal Ni2In-type paramagnetic (PM) phase to a low-temperature orthorhombic TiNiSi-type ferromagnetic (FM) phase which is tunable over wide temperature range by changing the Al content [1,2]. As melt spinning is a rapid solidification technique able to produce alloy ribbon samples with a high chemical homogeneity and may result very appropriate to fabricate these five-elements alloys, we produced Mn0.5Fe0.5NiSi1-xAlx melt-spun ribbons with x=0.055 and 0.060 that were thermally annealed at 1123 K for 4 h; their MST and MC characteristics were studied. RT XRD pattens show that samples are nearly single phase with a major Ni2In-type phase coexisting with a minor amount of the TiNiSi-type one. DSC, M(T)5mT and M(T)2T curves, shown in Fig. 1, denote the occurrence of the MST with a large thermal hysteresis (~ 32 K), the substantial effect of Al-content on the tuning of the MST temperature without a significant change in the magnetization change across the MST which led to similar Â½DSM(T)Â½max values (as Fig. 2 shows). The results are discussed and compared with previous data reported in literature for bulk alloys.

Magnetostructural transition and magnetocaloric effect in thermally annealed Mn0.5Fe0.5NiSi1 xAlx melt

Magnetic refrigeration (MR), exploiting the adiabatic demagnetization phenomena, is preferable over conventional cooling technology due to its high efficiency with environment friendly method [1-3]. Owing to this, the earth-abundant Mn-based alloys, i.e. Mn5Sn3, crystallizes in Ni2In type hexagonal structure (space group P63/mmc), occupies two non-equivalently sites with opposite spin alignment: MnI at 2a site with a moment of 0.8 Î¼B and MnII at 2(d) site with a moment of 3.8 Î¼B and Sn atom occupies 2c site. The temperature and field-dependent dc magnetization measurements have been carried out to study the MCE and exchange bias in Mn5Sn3 alloy. The M (T) curve at 100 Oe shows ordering temperature at Tc ~ 227 K and spin glass (SG) transition at Tg ~ 110 K [Fig. 1a]. The origin of SG is due to geometrical frustration, that comes from vacancy and disordering present at Mn2d site. Furthermore, the M (H) hysteresis loop at 5 K reveals the typical soft ferromagnetic behaviour, saturation magnetisation (MS) of 62 emu/g [Fig.1(b)], where MH loop slightly shifted towards a negative field direction, indicating the presence of exchange bias phenomena with exchange bias field (HEB) 5.67 mT at 50 K. Apart from this, Isothermal magnetic entropy change (Î”SM(T)) is (calculated Using Maxwell equation) 2.16 J/Kg-K at 5 T [Fig. 2], also Î”SM(T) evolve with applied magnetic field as - Î”SM(T) = aHn, where n is local exponent, power law fit gives n = 0.649 (1) [Inset of Fig 2(a)]. From Inset fig. 2(b), It is quite apparent that all the normalized entropy curves with various Î”H values collapse into a single curve, confirming second-order magnetic phase transition. The relative cooling power (RCP) value is obtained as 242 J/kg for a field change of 5 T which is significantly larger than the earlier reported Mn5Sn3 study [4]. Hence, with negligible thermal/magnetic hysteresis and reasonable RCP, the Mn5Sn3 is prominent candidate for MR devices.

Premium content

Tuning in the vast high entropy alloy space for competitive magnetocaloric properties

Downloads

Next from MMM 2022

Magnetoactive Properties of 3D Printed Magnetic Elastomer Structures: Effects of Infill Orientation and Infill Percentage

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES