Magnetic Texture in Insulating Single Crystal High Entropy Oxide Spinel Films
Yogesh Sharma, Alessandro R. Mazza, Brianna L. Musico, Elizabeth Skoropata, Roshan Nepal, Rongying Jin, Anton V. Ievlev, Liam Collins, Zheng Gai, Aiping Chen, M… 展开作者
Yogesh Sharma, Alessandro R. Mazza, Brianna L. Musico, Elizabeth Skoropata, Roshan Nepal, Rongying Jin, Anton V. Ievlev, Liam Collins, Zheng Gai, Aiping Chen, Matthew Brahlek, Veerle Keppens, Thomas Z. Ward
Magnetic insulators are important materials for a range of next generation memory and spintronic applications. Structural constraints in this class of devices generally require a clean heterointerface that allows effective magnetic coupling between the insulating layer and the conducting layer. However, there are relatively few examples of magnetic insulators which can be synthesized with surface qualities that would allow these smooth interfaces and precisely tuned interfacial magnetic exchange coupling which might be applicable at room temperature. In this work, we demonstrate an example of how the configurational complexity in the magnetic insulator layer can be used to realize these properties. The entropy-assisted synthesis is used to create single crystal (Mg0.2Ni0.2Fe0.2Co0.2Cu0.2)Fe2O4 films on substrates spanning a range of strain states. These films show smooth surfaces, high resistivity, and strong magnetic responses at room temperature. Local and global magnetic measurements further demonstrate how strain can be used to manipulate magnetic texture and anisotropy. These findings provide insight into how precise magnetic responses can be designed using compositionally complex materials that may find application in next generation magnetic devices.
Mg batteries with oxide cathodes have the potential to significantly surpass existing Li-ion technologies in terms of sustainability, abundance, and energy density. However, Mg intercalation at the cathode is often severely hampered by the sluggish kinetics of Mg$^{2+}$ migration within oxides. Here we report a combined theoretical and experimental study addressing routes to identify cathode materials with an improved Mg-ion mobility. Using periodic density functional theory calculations, Mg$^{2+}$ migration in oxide spinels has been studied, revealing key features that influence the activatio…
Polar phonons and intrinsic dielectric response of the ferromagnetic insulating spinel CdCr$_2$S$_4$ from first principles
本文从第一性原理出发研究了铁磁尖晶石CdCr $_2$ S $_4$的介电性质。在LSDA+U模型下，利用冻结声子和Berry相位技术计算了带心声子和玻恩有效电荷。我们发现，所有的红外活性声子是相当稳定的立方空间群内。计算的静态介电常数与以前的测量结果吻合得很好。这些结果表明，最近观察到的异常介电行为在CdCr $_2$ S $_4$是不是由于极性模式的软化。我们建议进一步的实验来阐明这一点。
Covalent Hybrid of Spinel Manganese-Cobalt Oxide and Gra-phene as Advanced Oxygen Reduction Electrocatalysts
通过在氮掺杂的还原氧化石墨烯片上直接成核和生长纳米颗粒以及阳离子取代尖晶石Co 3 O 4纳米颗粒，开发了锰-钴尖晶石MnCo 2 O 4/石墨烯杂化物作为碱性条件下氧还原反应（ORR）的高效电催化剂。电化学和X射线近边结构（XANES）研究表明，形成无机纳米碳杂化物的成核和生长方法导致尖晶石氧化物纳米颗粒和N掺杂的还原氧化石墨烯（N-rmGO）片之间的共价偶联。碳K边和氮K边XANES显示N-rmGO片中的C-O和C-N键强烈扰动，表明N掺杂的氧化石墨烯和尖晶石氧化物纳米颗粒之间形成C-O-金属和C-N-金属键。Co L-edge和Mn L-edge XANES分析表明，Mn 3+取代了Co 3+位，提高了杂化材料中催化位的活性，从而进一步提高了杂化材料的ORR活性.共价键合的杂化物比纳米颗粒和包括N-rmGO的碳材料的物理混合物提供更大的活性和耐久性。在相同的质量负载下，MnCo 2 O 4/N-graphene杂化物在中等过电位下的ORR电流密度可以超过Pt/C，并且在碱性溶液中具有优于Pt/C的稳定性。
Sintered samples of a spinel oxide LiFeCr4O8, where Cr3+ and Fe3+ ions have localized moments, were found to show a large magnetic-field-induced volume increase approaching 500 ppm by applying a magnetic field of 9 T. This large volume increase appeared only at around 30 K. At 30 K, a spin-reorientation transition from ferrimagnetic to conical order occurs, giving rise to this large volume increase. The coexistence of ferrimagnetic and conical phases at this transition was found to be important, suggesting that such a large magnetic-field-induced volume change can be realized at various magnet…
We report high temperature synchrotron X-ray diffraction (SXRD), dc magnetization and current-voltage (I-V) characteristics for the samples of Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite. The material was prepared by chemical reaction of the Fe and Co nitrate solutions at pH = 11 and subsequent annealing at temperatures 200 0C, 500 0C and 900 0C. The measurements were performed by cycling the temperature from 300 K to high temperature (warming mode) and return back to 300 K (cooling mode). The SXRD patterns indicated a fine bi-phased cubic spinel structure in the highly Co rich spinel oxide. Magnetiza…
Magneto-Structural Coupling Enables Cryogenic Cation Redistribution in a Spinel Oxide
Hainan University（海南大学）；Arizona State University（亚利桑那州立大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；Spallation Neutron Source Science Center（散裂中子源科学中心）；University of Science and Technology Beijing（北京科技大学）；Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所北京凝聚态物理国家实验室）
MgGa2O4 spinel barrier for magnetic tunnel junctions: coherent tunneling and low barrier height
采用磁控溅射法制备了Fe/MgGa 2 O 4/Fe（001）磁性隧道结。隧道磁电阻（TMR）的比率高达121%，在室温下（196%，在4 K）观察到，这表明在MgGa 2 O 4势垒的相干隧道效应的TMR增强。MgGa 2 O 4层具有尖晶石结构，并且由于MgGa 2 O 4的轻微的四方晶格畸变，其显示出与Fe层良好的晶格匹配。势垒厚度依赖性的隧穿电阻和电流-电压特性表明，MgGa 2 O 4势垒的势垒高度远低于MgAl 2 O 4势垒。这项研究表明，潜在的Ga基尖晶石氧化物的MTJ势垒具有大的TMR比在低电阻面积积。
Many positive electrode materials in lithium ion batteries include transition metals which are difficult to describe by electronic structure methods like density functional theory (DFT) due to the presence of multiple oxidation states. A prominent example is the lithium manganese oxide spinel Li$_x$Mn$_2$O$_4$ with $0\leq x\leq2$. While DFT, employing the local hybrid functional PBE0r, provides a reliable description, the need for extended computer simulations of large structural models remains a significant challenge. Here, we close this gap by constructing a DFT-based high-dimensional neural…
Influence of inversion on Mg mobility and electrochemistry in spinels
镁氧化物和硫化物尖晶石作为能量密度镁电池的阴极和电解质材料最近引起了人们的兴趣，但它们观察到的电化学性能强烈依赖于合成条件。利用第一性原理计算和逾渗理论，我们探索在何种程度上尖晶石反转影响Mg $^{2+}$离子迁移率在MgMn $_2$ O $_4$作为原型阴极，和MgIn $_2$ S $_4$作为潜在的固体电解质。我们发现，尖晶石反转和由此产生的局部阳离子有序的变化引起的增加和减少Mg $^{2+}$迁移障碍，沿特定的迁移途径，在氧化物以及硫化物。为了量化尖晶石反转对宏观Mg $^{2+}$传输的影响，我们确定了MgMn $_2$ O $_4$和MgIn $_2$ S $_4$中的逾渗阈值。此外，我们分析的电化学性能的MgMn $_2$ O $_4$阴极通过相行为的变化，平均Mg插入电压和可提取的容量，在不同程度的反转的反转的影响。我们的研究结果证实，反转是镁尖晶石的主要性能限制因素，并且稳定有序尖晶石结构的合成技术或组合物对于镁尖晶石在多价电池中的成功至关重要。
Disentangling the contributions of individual cations to magnetic order in a spinel high entropy oxide
University of British Columbia（不列颠哥伦比亚大学）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；University of Saskatchewan（萨斯喀彻温大学）；Canadian Light Source（加拿大光源）
用光谱法研究了ACr_2 O_4铬尖晶石氧化物磁性半导体在T=10- 335 K宽温区的晶格结构动力学性质。A位离子（A=Mn，Fe，Co，Ni和Cu）的系统变化表明，3d轨道在A位的占据对晶格动力学有很大影响。对于具有轨道简并的化合物（FeCr 2 O 4、NiCr 2 O 4和CuCr 2 O 4），在Jahn-Teller转变和随后的长程磁序开始时，观察到红外活性声子模式的清晰分裂和/或沉默振动模式的激活。虽然MnCr 2 O 4和CoCr 2 O 4显示出多铁性和磁电特性，但在没有轨道简并的尖晶石化合物中没有发现相当大的磁弹性，因为它们即使在其磁性基态也紧密地保持高温立方尖晶石结构。除了晶格振动，还研究了A $^{2+}$离子的原子内3d-3d跃迁，以确定晶体场和Racah参数以及自旋轨道耦合的强度。
We experimentally investigated the magnetic properties of NiCo$_2$O$_4$ epitaxial films known to be conductive oxides with perpendicular magnetic anisotropy (PMA) at room temperature. Both magneto-torque and magnetization measurements at various temperatures provide clear experimental evidence of the spin reorientation transition at which the MA changes from PMA to easy-cone magnetic anisotropy (ECMA) at a certain temperature ($T_{\rm{SR}}$). ECMA was commonly observed in films grown by pulsed laser deposition and reactive radio frequency magnetron sputtering, although $T_{\mathrm{SR}}$ is dep…
Breathing Pyrochlore Lattice Realized in A-Site Ordered Spinel Oxides LiGaCr4O8 and LiInCr4O8
在两种A位有序尖晶石氧化物LiGaCr 4 O 8和LiInCr 4 O 8中发现了一种独特的阻挫晶格。由于Li+和Ga 3 +/In 3+离子在A位处的大尺寸失配，由携带自旋3/2的Cr 3+离子组成的烧绿石晶格变成小四面体和大四面体的交替阵列，即，“呼吸”烧绿石晶格。我们引入了一个参数，呼吸因子Bf，它量化了烧绿石晶格中的挫折程度：Bf被定义为J '/J，其中J'和J是最近邻的磁相互作用在大，小四面体，分别。具有Bf ~ 0.6的LiGaCr 4 O 8显示出与常规Cr尖晶石氧化物如ZnCr 2 O 4类似的磁化率。与此相反，LiInCr 4 O 8与一个小的Bf ~ 0.1的磁化率表现出自旋带隙的行为，表明接近一个奇特的单重基态。磁长程序发生在13.8和15.9 K的LiGaCr 4 O 8和LiInCr 4 O 8，分别，在这两种情况下可能是由于耦合到结构扭曲。
Spinel oxides are an ideal setting to explore the interplay between configurational entropy, site selectivity, and magnetism in high entropy oxides. In this work we characterize the magnetic properties of the spinel (Cr,Mn,Fe,Co,Ni)$_3$O$_4$ and study the evolution of its magnetism as a function of non-magnetic gallium substitution. Across the range of compositions studied here, from 0% to 40% Ga, magnetic susceptibility and powder neutron diffraction measurements show that ferrimagnetic order is robust in the spinel HEO. However, we also find that the ferrimagnetic order is highly tunable, wi…
High-temperature Cu-Mn-Fe spinel-oxide nanoparticle solar selective absorber coatings are investigated experimentally and theoretically. A reliable, general approach to evaluate absorption coefficient spectra from the optical measurements of the nanoparticle-pigmented coatings is developed based on solving the inverse problem using four-flux-radiative method. The derived absorption properties of NP materials can be directly applied to predict the solar absorptance, optimize the nanoparticle-pigmented coatings, and analyze the thermal degradation, which agree well with the experimental results.…
Superconductivity in spinel oxide LiTi2O4 epitaxial thin films
LiTi 2 O 4是一种独特的材料，因为它是唯一已知的氧化物尖晶石超导体。虽然体材料研究已经表明超导性可以用Bardeen-Cooper-Schreiffer理论来描述，但是超导性的微观机制还没有完全解决。超导性能对尖晶石晶体结构的各种缺陷的敏感性提供了对这种机制的深入了解。在MgAl 2 O 4、MgO和SrTiO 3单晶衬底上的LiTi 2 O 4外延膜提供了系统地探索晶格应变和微结构无序的影响的模型系统。影响带宽的晶格应变引起超导和正常状态性质的有限变化。微结构无序如反相晶界引起的Ti网络无序可降低临界温度，但Ti网络无序与Mg互扩散相结合对超导态的影响更为显著。厚度相关的运输研究表明，超导体-绝缘体的转变作为膜厚度的函数，而不管晶格应变和微观结构。此外，表面敏感的X射线吸收光谱已确定Ti保留站点对称性和平均价的散装材料，而不管膜厚度。
High-performance thermoelectric oxides could offer a great energy solution for integrated and embedded applications in sensing and electronics industries. Oxides, however, often suffer from low Seebeck coefficient when compared with other classes of thermoelectric materials. In search of high-performance thermoelectric oxides, we present a comprehensive density functional investigation, based on GGA$+U$ formalism, surveying the 3d and 4d transition-metal-containing ferrites of the spinel structure. Consequently, we predict MnFe$_2$O$_4$ and RhFe$_2$O$_4$ have Seebeck coefficients of $\sim \pm …
Ni incorporation has been studied in a comprehensive range of Zn/Co-based magnetic oxides to elucidate it valence state and lattice incorporation. The resulting structural and magnetic properties are studied in detail. To the one end Ni in incorporated by in-diffusion as well as reactive magnetron co-sputtering in wurtzite ZnO where only the Ni-diffused ZnO exhibits significant conductivity. This is complemented by Ni and Co codoping of ZnO leading. To the other end, the ZnCo$_2$O$_4$ spinel is co-doped with varying amounts of Ni. In the wurtzite oxides Ni is exclusively found on tetrahedral l…
Ultra-Soft Ferrimagnetism in a High-Entropy Spinel Oxide Driven by Site-Selective Cation Disorder
Thapar Institute of Engineering and Technology（塔帕尔工程技术学院）；UGC-DAE Consortium for Scientific Research（UGC-DAE科学研究联盟）；Univ. Bordeaux, CNRS, Bordeaux INP, ICMCB, UMR 5026（波尔多大学、法国国家科学研究中心、波尔多国立理工学院、材料与化学研究组合中心）；Laboratory Crismat, UMR6508 CNRS, Normandie University, ENSICAEN, UNICAEN（Crismat实验室、法国国家科学研究中心联合研究实验室6508、诺曼底大学、恩西辛高等学院、卡昂大学）
High-temperature concentrating solar power (CSP) system is capable of harvesting and storing solar energy as heat towards cost-effective dispatchable solar electricity. Solar selective coating is a critical component to boost its efficiency by maximizing solar absorptance and minimizing thermal emittance losses. However, maintaining a high solar-thermal conversion efficiency >90% for long-term operation at >750 degrees C remains a significant challenge. Herein, we report spray-coated spinel Cu-Mn-Cr oxide nanoparticle-pigmented solar selective coatings on Inconel tube sections maintaining >94%…
Comparative Study of Optical and Magneto-Optical Properties of Normal, Disordered and Inverse Spinel Type Oxides
采用脉冲激光沉积法在高温和低温下制备了Co $_3$ O $_4$、ZnFe $_2$ O $_4$、CoFe $_2$ O $_4$、ZnCo $_2$ O $_4$和Fe $_3$ O $_4$薄膜，得到了具有光滑表面形貌的正、反以及无序的单相尖晶石氧化物薄膜。在0.5 ~ 8.5 eV的宽光谱范围内用椭圆偏振光谱法测定了介电函数，并与在1.7 T的磁场下用磁光克尔效应（MOKE）光谱法在1.7 ~ 5.5 eV的光谱范围内测定的介电张量的磁光响应进行了比较。晶场，价间和亚晶格间电荷转移跃迁，从O $_{2p}$过渡到金属阳离子3d或4s带被确定在主对角线元素和磁光活性非对角线元素的介电张量。取决于阳离子无序的程度，导致局部对称性畸变，磁光响应被认为是最强的高晶体质量的反尖晶石和无序的正常尖晶石结构，相反的第一原理研究的CoFe $_2$ O $_4$和ZnFe $_2$ O $_4$。研究结果为更深入地理解这种材料系统中的光-物质相互作用提供了基础，这种材料系统对与器件相关的现象和工程至关重要。
Electronic structure of normal and inverse spinel ferrites from first principles
采用自相互作用修正的局域自旋密度近似（SIC-LSD）方法研究了尖晶石铁氧体MnFe $_{2}$ O $_{4}$，Fe $_{3}$ O $_{4}$，CoFe $_{2}$ O $_{4}$，NiFe $_{2}$ O $_{4}$的电子结构和磁性.我们专注于建立过渡金属元素的名义价态和基态结构，基于对所有系统的反尖晶石结构和正常尖晶石结构的各种价态方案的研究。对于这两种结构，我们发现所有研究的化合物都是绝缘的，但在正常的尖晶石方案中具有较小的间隙。相反，计算的自旋磁矩和交换分裂的导带被认为是急剧增加时，从反尖晶石结构的正常尖晶石类型。发现NiFe $_{2}$ O $_{4}$和CoFe $_{2}$ O $_{4}$的轨道矩很大。
Enhanced magnetic moment and conductive behavior in NiFe2O4 spinel ultrathin films
块状NiFe 2 O 4是一种绝缘亚铁磁体。在这里，我们报告的尖晶石NiFe 2 O 4薄膜上SrTiO 3单晶的外延生长。我们将表明，在适当的生长条件下，外延稳定导致形成的尖晶石相的磁性和电学性质，从根本上不同的散装材料：增强的磁矩（Ms）-约250%以上-和金属字符。的厚度依赖性的MS的系统研究允许得出结论，其增强的值是由于一个异常分布的Fe和Ni阳离子之间的尖晶石结构的A和B网站导致从非平衡生长条件和界面效应。尖晶石，更一般地说，氧化物为基础的异质结构的这些发现的相关性进行了讨论。我们认为，这种新材料可能是一种替代铁磁金属电极在磁性隧道结。
Lithium ion batteries often contain transition metal oxides like Li$_{x}$Mn$_2$O$_4$ ($0\leq x\leq2$). Depending on the Li content different ratios of Mn$^\text{III}$ to Mn$^\text{IV}$ ions are present. In combination with electron hopping the Jahn-Teller distortions of the Mn$^\text{III}$O$_6$ octahedra can give rise to complex phenomena like structural transitions and conductance. While for small model systems oxidation and spin states can be determined using density functional theory (DFT), the investigation of dynamical phenomena by DFT is too demanding. Previously, we have shown that a hi…
Antiferromagnetic transition metal oxides are an established and widely studied materials system in the context of spin-based electronics, commonly used as passive elements in exchange bias-based memory devices. Currently, major interest has resurged due to the recent observation of long-distance spin transport, current-induced switching, and THz emission. As a result, insulating transition metal oxides are now considered to be attractive candidates for active elements in novel spintronic devices. Here, we discuss some of the most promising materials systems and highlight recent advances in re…
From Chemical Complexity to Tunable Magnetic Ordering in Highly Disordered High-Entropy Spinel Oxides
Thapar Institute of Engineering and Technology（塔帕尔工程技术学院）；UGC-DAE Consortium for Scientific Research（UGC-DAE科学研究联盟）；Freie Universität Berlin（柏林自由大学）；Helmholtz Zentrum Berlin für Materialien und Energie（柏林亥姆霍兹材料与能源中心）；Normandie University（诺曼底大学）
We report neutron scattering measurements of the spinel oxide LiGaCr$_{4}$O$_{8}$, in which magnetic ions Cr$^{3+}$ form a breathing pyrochlore lattice. Our experiments reveal the coexistence of a nearly dispersionless resonance mode and dispersive spin wave excitations in the magnetically ordered state, which can be quantitatively described by a quantum spin model of hexagonal loops and linear spin wave theory with the same set of exchange parameters, respectively. Comparison to other Cr spinel oxides reveals a linear relationship between the resonance energy and lattice constant across all t…
Magnetic insulators with strong perpendicular magnetic anisotropy (PMA) play a key role in exploring pure spin current phenomena and developing ultralow-dissipation spintronic devices, thereby it is highly desirable to develop new material platforms. Here we report epitaxial growth of La2/3Sr1/3MnO3 (LSMO)-SrIrO3 (SIO) composite oxide films (LSMIO) with different crystalline orientations fabricated by sequential two-target ablation process using pulsed laser deposition. The LSMIO films exhibit high crystalline quality with homogeneous mixture of LSMO and SIO at atomic level. Ferrimagnetic and …
Ferromagnetic insulators (FMIs) are one of the most important components in developing dissipationless electronic and spintronic devices. However, since ferromagnetism generally accompanies metallicity, FMIs are innately rare to find in nature. Here, novel room-temperature FMI films are epitaxially synthesized by deliberate control of the ratio of two B-site cations in the double perovskite Sr2FeReO6. In contrast to the known ferromagnetic metallic phase in stoichiometric Sr2FeReO6, a FMI state with a high Curie temperature (Tc~400 K) and a large saturation magnetization (MS~1.8 μB/f.u.) is fo…
Accurate first-principles predictions of the structural, electronic, magnetic, and electrochemical properties of cathode materials can be key in the design of novel efficient Li-ion batteries. Spinel-type cathode materials Li$_x$Mn$_2$O$_4$ and Li$_x$Mn$_{1.5}$Ni$_{0.5}$O$_4$ are promising candidates for Li-ion battery technologies, but they present serious challenges when it comes to their first-principles modeling. Here, we use density-functional theory with extended Hubbard functionals - DFT+$U$+$V$ with on-site $U$ and inter-site $V$ Hubbard interactions - to study the properties of these …
