Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Y36: Magnetic Anisotropy: Measurement, Materials and DevicesFocus Session Live
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Sponsoring Units: GMAG DMP Chair: Lorenzo Fallarino, CIC nanoGUNE |
Friday, March 19, 2021 11:30AM - 11:42AM Live |
Y36.00001: Anatomy of Voltage-Controlled Magnetic Anisotropy in Heterostructures with Atomically-Thin Heavy Metals Sohee Kwon, QILONG SUN, Farzad Mahfouzi, Kang-Lung Wang, Pedram Khalili Amiri, Nicholas Kioussis The demand for higher speed, higher density, and more energy-efficient magnetoelectric random access memory (MeRAM) requires the urgent search of novel materials and magnetic tunnel junction with voltage-controlled magnetic anisotropy (VCMA) efficiency greater than 1000 fJ/(Vm). Employing ab initio electronic structure calculations we propose a MgO/X/FeCo/MgO heterostructure, where X is an atomically-thin late transition metal (Ir, Pt, Rh), which exhibits both giant perpendicular magnetic anisotropy (PMA) and VCMA efficiency, where the former (latter) is one (one to two) order of magnitude higher than the values reported to date. We demonstrate that the dominant contribution to both the PMA and VCMA arises from the heavy metal X due to the large biaxial tensile strain-induced magnetism in X. These findings provide useful guiding rules in exploiting the large SOC and biaxial tensile strain-induced magnetism in the late transition metals for the design of the next-generation of ultra-low energy MeRAM devices. |
Friday, March 19, 2021 11:42AM - 11:54AM Live |
Y36.00002: Determination of anisotropy constants of ferromagnetic multilayers via fitting of Stoner-Wohlfarth Model Sean Peterson, Yves Ulrich Idzerda Historically the primary method of determining the anisotropy constants of a material has been the angle dependence of the Ferromagnetic Resonance (FMR), which makes use of the Larmor frequency of a spin precessing around an applied magnetic field. Anisotropy constants can also be determined by fitting the hysteresis curves to those predicted by the Stoner-Wohlfarth Model via a least-squares fitting algorithm. In this work the anisotropy energy was considered for both the bulk and the interface of ferromagnetic films. Preliminary results find the interface anisotropy constant of alloys of Fe, Co, and Mn to be larger than the bulk anisotropy, both of which are on the order of nanoJoules. This methodology also allows for the determination of the coupling constant between the layers of a multilayered system. This is the main advantage of this method over FMR. It should also be noted that magnetic hysteresis data is much more readily available than FMR data due to its specialized nature, opening up the possibilities of determining the anisotropy and coupling constants for a larger variety of samples. |
Friday, March 19, 2021 11:54AM - 12:06PM Live |
Y36.00003: First Principles Study of Magnetic Properties of Cr1+δTe2 Zi Chao Huang, Jian Feng Kong, Yuita Fujisawa, Yoshinori Okada, Anjan Soumyanarayanan, Khoong Hong Khoo Recent experimental efforts have demonstrated growth of Cr1+δTe2 films in the NiAs-type crystal structure over a wide range of δ values. This has motivated our investigation of magnetic exchange and magnetic anisotropy interactions as well as the Curie temperature of Cr1+δTe2 at various doping levels using first principles density functional theory calculations. Our results show good agreement with experimental results, with Tc increasing with δ and systems showing perpendicular magnetic anisotropy for δ < 0.43. In addition, we have been able to gain insight into the origins of the magnetic properties from an electronic structure perspective. We show that there are significant ferro and anti-ferromagnetic interactions within the Cr1+δTe2 compounds and that magnetic anisotropy is largely dominated by the electronic structure of Te atoms. |
Friday, March 19, 2021 12:06PM - 12:18PM Live |
Y36.00004: Magnetic anisotropy modification in a garnet ferrimagnet by interfacial spin orbit coupling Guanzhong Wu, Dongying Wang, Nish Verma, Yang Cheng, Side Guo, Guixin Cao, Kenji Watanabe, Takashi Taniguchi, Chun Ning Lau, Fengyuan Yang, Mohit Randeria, Marc Bockrath, P Chris Hammel Y3Fe5O12 (YIG) is a ferrimagnetic insulator with substantial potential in realizing pure spin-based information processing and storage exceptionally low Gilbert damping. This contributes to its potential for enabling pure spin-based information processing and storage. Interfacial interactions can induce magnetic anisotropy is in this cubic material. When a nonmagnetic heavy metal is deposited on YIG, an additional easy-plane anisotropy arising from the Rashba spin orbit coupling (SOC) is induced. Here we report that a perpendicular magnetic anisotropy (PMA) is induced at the interface between YIG and a low symmetry high SOC semimetal, WTe2. The PMA in the YIG/WTe2 heterostructure is rooted in the broken inversion symmetry in the WTe2 crystal lattice, which gives rise to an additional SOC that was previously reported to enable an out-of-plane spin orbit torque. In addition, we study the spin pumping across the YIG/WTe2 interface and find that its strength is independent of the WTe2 thickness. Our study suggests that SOC arising from the broken crystalline symmetry in WTe2 plays crucial role in modifying the interfacial magnetic anisotropy and in spin relaxation at the interface. |
Friday, March 19, 2021 12:18PM - 12:30PM Live |
Y36.00005: New Co-Fe-N Magnetic Compounds Found Through Combined Computational and Experimental Methods Balamurugan Balasubramanian, Rabindra Pahari, Cai-Zhuang Wang, Xiaoshan Xu, Kai-Ming Ho, David J Sellmyer A combined search using computational and non-equilibrium cluster-deposition methods has been efficient in accelerating the discovery of new magnetic materials with high magnetocrystalline anisotropy K1, large saturation magnetic polarization Js, and high Curie Temperature Tc [1, 2]. Here we present the structure and magnetism of new compounds created by incorporating nitrogen and/or silicon in the interstitial or substitutional occupancies of Co, Fe, and FeCo. The search found a set of Fe-Co-N compounds having promising magnetic properties, including tetragonal Fe8Co8N2 that exhibits K1 = 16 Mergs/cm3, Js = 17.6 kG, and Tc ≈ 650 K. The prospects of new rare-earth magnetic compounds for energy and information storage applications will be discussed. |
Friday, March 19, 2021 12:30PM - 12:42PM Live |
Y36.00006: Monte Carlo Simulations Exploring the Impact of Anisotropy on the Equilibrium Properties of Magnetic Tunnel Junction-Based Molecular Spintronics Device Bishnu Dahal, Marzieh Savadkoohi, Andrew Grizzle, Uzma Amir, Pius Suh, Christopher D’Angelo, Pawan Tyagi Magnetic tunnel junction molecular-based spintronics device (MTJMSD) may allow the realization of novel magnetic metamaterials and the miniaturization to nanoscale. Our Monte Carlo Simulation (MCS) is designed to study wide range of MTJMSDs that can be realized by combining a large variety of ferromagnetic (FM) electrodes and magnetic molecules. This MCS study represents covalently bonded paramagnetic molecules across the edges of the magnetic tunnel junction (MTJ) with two FMs. We have studied MTJMSDs properties by simulating various material factors such as anisotropy, FM-molecular coupling, thermal energy, etc. Our study focused on understanding the effect of anisotropy of the FM electrodes on the overall MTJMSDs at various temperatures. Our study shows that the multiple domains of opposite spins start to appear on an FM electrode as the anisotropy energy increases. The observation of magnetic domains with starkly different spins were observed around the molecular junction on the FM electrode with high anisotropy. These domains occurred when anisotropy energy was >20% of the Curie energy of the FM electrode. The effect of anisotropy keeps high magnetization of the device close to Curie temperature even when all the coupling effects get nullified due to thermal agitation. |
Friday, March 19, 2021 12:42PM - 12:54PM Live |
Y36.00007: Large anisotropic magnetocaloric effect of MnP alloy: A theoretical study Hung Tran, Tetsuya Fukushima, Hiroyoshi Momida, Kazunori Sato, Yukihiro Makino, Tamio Oguchi Magnetocaloric effect has attracted great attention as a promising method for future refrigeration with high power and efficiency. The conventional magnetocaloric materials are heated up or cooled down by applying or removing an external magnetic field. On the other hand, the temperature of a rotating magnetocaloric system can be modified by changing the direction of the external magnetic field. Several rotating magnetocaloric materials have been reported in the previous experimental works, motivating us to study the rotating magnetocaloric effect in a theoretical framework. The rotating magnetocaloric effect of MnP is studied by combining first-principles calculations and Monte-Carlo simulations. The magnetocrystalline anisotropy energy is not negligible even above the Curie temperature due to the effect of the magnetic field. The dependence of the isothermal magnetic entropy change on the direction is calculated with the Maxwell relation [1-2]. The magnetic entropy changes by rotating the sample are reasonably predicted and underlying mechanisms for the effect are discussed in detail. |
Friday, March 19, 2021 12:54PM - 1:06PM Live |
Y36.00008: Usage of Ce for the intrinsic properties of rare-earth permanent magnets Munehisa Matsumoto, Hiroaki Shishido Utilities of valence fluctuation effects in Ce are identified for magnetic anisotropy, magnetization, Curie temperature, and structure stability, all of which are of crucial importance in rare-earth permanent magnets. Enhancement of an intrinsic coercivity is demonstrated on the Co-rich side of Ce(Co,Cu)5 experimentally and correspondingly we show theoretically that the crossover near a valence transition of Ce brings about an order of magnitude enhanced magnetic anisotropy. Magnetization can actually benefit from Ce4+ with the volume effect and a particular site preference in the multiple-sublattice ferromagnets being taken into account. There can be a trade-off among those preferred properties for rare-earth permanent magnets and we discuss a resolution of it based on an importance sampling approach in the virtual materials space. |
Friday, March 19, 2021 1:06PM - 1:18PM Live |
Y36.00009: Tailoring magnetism in self-intercalated Cr1+δTe2 epitaxial films Yuita Fujisawa, Markel Pardo Almanza, Jennifer Garland, Kohei Yamagami, Xing Zhu, Xiaoye Chen, Kosei Araki, Takahito Takeda, Masaki Kobayashi, Yukiharu Takeda, Chia-Hsiu Hsu, Feng-Chuan Chuang, Robert Laskowski, Amy Khoo, Anjan Soumyanarayanan, Yoshinori Okada Controlling magnetic properties, including Curie temperature and magnetic anisotropy, in two dimensional ferromagnets are highly demanded for spintronics application. Here, we investigated magnetic properties of Cr1+δTe2 epitaxial films with varying δ. We found enhancement of Curie temperature above room temperature and rotation of magnetic anisotropy from out-of-plane to in-plane. Theoretical calculations suggest that anti-ferromagnetic interaction perpendicular to plane direction becomes stronger as increasing δ, which plays an important role in the experimental observations. |
Friday, March 19, 2021 1:18PM - 1:30PM Live |
Y36.00010: The Néel vector control in antiferromagnetic CrSb by electron filling, strain, and electric field In Jun Park, Sohee Kwon, Roger Lake CrSb is interesting for antiferromagnetic (AFM) spintronic applications due to its layered spin texture with perpendicular magnetic anisotropy, high Néel temperature, and large spin-orbit coupling (SOC). We performed density functional theory calculations to investigate the effects of strain, band filling, and electric field on the magnetic anisotropy energy (MAE) of bulk and thin-film CrSb. The MAE of bulk is large so that depleting electron can switch the Néel vector of bulk CrSb. Truncating the bulk structure to a thin film results in the broken inversion symmetry and the creation of a built-in electric field due to a large charge dipole. Moreover, the thin film exhibits broken spin degeneracy so that it becomes a ferrimagnet. Reduction of MAE makes the orientation of Néel vector switched with realistic strain. The MAE of the thin film can be changed by electric field via voltage controlled magnetic anisotropy (VCMA) due to the large SOC [1]. |
Friday, March 19, 2021 1:30PM - 1:42PM Live |
Y36.00011: Magnetic Anisotropy, Anisotropic Magnetoresistance, and Planar Hall Effect in Phase-Separated (La1-yPry)1-xCaxMnO3 Thin Films Ashkan Paykar, Amlan Biswas Phase competition between the ferromagnetic metallic (FMM) and charged order insulating (COI) phases of the perovskite manganite (La1-yPry)1-xCaxMnO3 (LPCMO) has led to the observation of unique electronic and magnetic properties. In addition, the coupling between its electronic and magnetic properties give rise to the possibility of tuning its magnetic properties, such as magnetic anisotropy, using electric fields. Thin films of (La0.5Pr0.5)0.67Ca0.33MnO3 were grown on (110) NdGaO3 (NGO) using pulsed laser deposition to investigate these phenomena. The NGO substrate exerts anisotropic in-plane strain which results in uniaxial, in-plane magnetic anisotropy and a single-domain to multi-domain transition in the FMM regions as they percolate at low temperatures. We observed anisotropic magnetoresistance (AMR) associated with the magnetic anisotropy at low magnetic fields. Measurements at higher magnetic field showed a reduction in the AMR, which suggests a combined effect of both magnetic anisotropy and phase separation. The planar Hall effect (PHE) in these samples enabled us to measure the voltage dependence of magnetic anisotropy due to electric field induced dynamic percolation. |
Friday, March 19, 2021 1:42PM - 1:54PM Live |
Y36.00012: Intrinsic Exchange Bias in Epitaxial CoFe2O4/Al2O3 thin film Detian Yang, Yu Yun, Xiaoshan Xu Exchange bias (EB), traditionally known as an interface phenomenon between ferro- or ferrimagnetic (FM) materials and antiferromagnetic (AFM) materials, has been widely applied in magnetic storage and spintronic devices. As one striking emergent phenomenon of oxide interfaces featured by strong interactions and reconstruction among spins, charges and lattice, “intrinsic” EB (IEB) effect without a nominal AFM layer has drawn much attention. To elucidate the mechanism of IEB, we grew CoFe2O4 (111) thin films epitaxially on sapphire (0001) substrates by pulsed laser deposition and studied their magnetic and structural properties. EB was observed when the magnetic field is in both the out-of-plan and the in-plane direction. The structural analysis using time-resolved reflection high energy electron diffraction during the growth, suggests that an AFM layer has developed between the substrate and the CoFe2O4 thin film. The power-law of the thickness-dependence of IEB indicate the interfacial origin. The temperature dependences of IEB and coercivity indicate a structural phase transition emerges at about 25 K. This work suggests a potential application of adjustable EB and provide new platforms to probe the mechanism of intrinsic EB. |
Friday, March 19, 2021 1:54PM - 2:06PM Live |
Y36.00013: Novel database driven method for discovering new Co-based ferromagnets Journey Byland, Yunshu Shi, Shaoqing Ding, Rogelio Mata, Haley E Magliari, David Parker, Andriy Palasyuk, Sergey Budko, Paul C Canfield, Peter Klavins, Valentin Taufour Magnetic elements are rare, and the best way to predict novel magnetic materials is to constrain a search to analyzing the magnetic properties of compounds containing magnetic elements such as rare-earth elements, iron, cobalt, or manganese. While many databases exist for the purposes of analyzing structural properties of compounds, databases of magnetic materials are either outdated or incomplete. The magnetic properties of 13,796 compounds containing the element cobalt have been gathered through a literature search, with the goal to complete the entire list or Co compounds. A total of 1,389 ferromagnetic compounds have been found and catalogued. Structure types, lattice parameters, cobalt percentage, and lattice angles of each compound were also collected; the shortest cobalt-cobalt bond lengths within the crystal lattice were calculated; and data trends were analyzed to predict novel ferromagnetic and anisotropic compounds. From this data, we illustrate how we discovered new ferromagnets with Curie temperature above room temperature, and uniaxial anisotropy. |
Friday, March 19, 2021 2:06PM - 2:18PM Live |
Y36.00014: Suppression of first-order transition and large magnetocaloric effect in Mn50-xNi40In10+x Zachary J Lehmann, Matthew Flesche, Tula Paudel, Parashu Kharel Magnetic materials exhibiting large entropy change at the second-order phase transition (SOPT) near room temperature have attracted much attention because these materials are free from magnetic and thermal hysteresis, and may show large cooling efficiency. We have investigated Mn50-xNi40In10+x alloys prepared by arc melting and vacuum annealing. The x-ray diffraction patterns analyzed using the Rietveld method shows that the samples crystallized in the cubic structure at room temperature. The thermomagnetic curves M(T) measured at μ0H = 0.1T show that the first-order phase transition observed in the parent compound Mn50-xNi40In10+x (x = 0) can be completely suppressed when x reaches 6. We observed large values of peak magnetic entropy change (ΔSM,max) and relative cooling power (RCP) measured at 3 T for Mn44Ni40In16 at 320 K. The measured values of ΔSM,max and RCP are comparable to those of other Gd-free compounds showing magnetocaloric effect due to SOPT near room temperature. This suggests that the Mn50-xNi40In10+x alloys have potential for room temperature magnetic refrigeration. |
Friday, March 19, 2021 2:18PM - 2:30PM Live |
Y36.00015: Magnetic and structural properties of Co(Fe)-Ni-Al(Ga) Heusler alloys Olga Miroshkina, Markus Gruner, Vasiliy D Buchelnikov, Vladimir V Sokolovskiy Ferromagnetic shape memory alloys (FSMA) are promising candidates for application as actuators, sensors, magnetomechanical devices, harvesters, and magnetic cooling systems. In their low-temperature, low-symmetry phases they may also posses a considerable magnetocrystalline anisotropy, which is necessary for the FSMA but may render them useful as low-cost permanent magnets as well. Co(Fe)-Ni-Al(Ga) alloys are an interesting subgroup, as these materials are ductile, cheap, and easily synthesized, while possessing a high Curie and martensitic transformation temperature. In this work, we report on systematic first-principle investigations of the structural and magnetic properties of Co2NiAl, Fe2NiAl, and Fe2NiGa-based Heusler alloys. We calculated the ground state energy and magnetic properties of different structural motives and degree of order. For the most favorable structures, we evaluated magnetocrystalline anisotropy, magnetic exchange coupling and lattice free energy to assess the equilibrium properties for the compositions under study. |
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