Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G47: Antiferromagnetic Oxide Thin Films for SpintronicsFocus
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Sponsoring Units: GMAG DMP DCOMP Chair: Kelly Luo, Cornell University Room: 710/712 |
Tuesday, March 3, 2020 11:15AM - 11:27AM |
G47.00001: Non-magnetic Origin of Spin Hall Magnetoresistance in Pt films and Epitaxial NiO/Pt bilayers Alexandra Churikova, David Bono, Brian Neltner, Larry Scipioni, Adam Shepard, Angela Wittmann, Felix Buettner, Ty Newhouse-Illige, James Greer, Geoffrey Beach Recently, electrical control of the magnetic order in antiferromagnetic insulators (AFIs) with a Pt overlayer as a spin current source has been a subject of great interest [1-4], as it allows for ultra-low power control of the magnetic order. However, the detection and nature of purely AFI magnetoresistive switching remains elusive [5-6]. Here, we show that the Pt signal has a strong bias due to the device-dependent current distribution and subsequent electromigration. We determine the effect of current density and magnetic layer thickness on the spin Hall magnetoresistance magnitude and signal shape of both Pt films and NiO(111)/Pt bilayers grown on sapphire substrate. The signal in both materials has a strong temperature dependence, and an exponential dependence on current, indicating the presence of thermally activated mechanisms. We suggest that more sophisticated techniques that directly probe the magnetic order are required to infer information about the AF magnetic state in such systems. |
Tuesday, March 3, 2020 11:27AM - 11:39AM |
G47.00002: Anisotropic Magnetoresistance and Nontrivial Spin Magnetoresistance in Pt/α-Fe2O3 Bilayers Sisheng Yu, Yang Cheng, Adam S Ahmed, Menglin Zhu, Jinwoo Hwang, Fengyuan Yang Recently antiferromagnetic insulators(AFM) play an import role in spintronic research including the spin superfluid and long distance spin transport. However, magnetic proximity effect (MPE) has not been conclusively observed in antiferromagnet based systems. In this work, we observed anomalous Hall effect and anisotropic magnetoresistance in angular dependent magnetoresistance (ADMR) measurements in Pt on antiferromagnetic (AF) α-Fe2O3(0001) epitaxial thin films at 10 K, which provide evidence for the MPE[1]. The Néel order of α-Fe2O3 and the induced magnetization in Pt show a unique ADMR compared with all other FM and AF systems. A macrospin response model is established and can explain the AF spin configuration and all main ADMR features in the Pt/α-Fe2O3 bilayers. |
Tuesday, March 3, 2020 11:39AM - 11:51AM |
G47.00003: Magnetic anisotropy in a single crystal antiferromagnetic thin film Saima Siddiqui, john pearson, Axel Hoffmann Antiferromagnetic (AF) materials promise to show magnetization dynamics, including switching, at ultra-high frequency and thus are of immense interest for next generation memory and logic applications. Besides, spin waves in AF insulators propagate very efficiently. However, electrically reading the states of the AF materials is not easy. Recently, spin Hall magnetoresistance (SMR) has been identified as one of the promising ways to access the surface states of the AF insulators. In this work, we deposit α-Fe2O3 (200 nm)/Pt (6 nm) on (11-20) Al2O3. We measure SMR of Pt Hall bar on Fe2O3. Below Morin transition temperature, we observe positive and negative magnetoresistance in the Pt/Fe2O3 bilayers depending on the direction of the electrical currents at the spin flop transition. This identifies that SMR can clearly determine the anisotropy of thin film AF insulators. We will show the detail study of the dependence of magnetoresistance on angular fields at different temperatures. Our study reveals important physical phenomena in AF Fe2O3 thin film. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G47.00004: Néel vector switching in enhanced-TN magnetoelectric thin films Ather Mahmood, Will Echtenkamp, Junlei Wang, Christian Binek Controlling magnetism by electrical means is a key challenge in the field of spintronics and essential for energy efficient devices in computing. Voltage-controlled switching of magnetization is manifested through boundary magnetization in Cr2O3 and promises non-volatile spintronic memory and logic devices. In pure Cr2O3, switching of the state variable takes place through magnetoelectric reversal of the Néel vector but the operation is limited to T< 307 K. In contrast, in B-doped Cr2O3, toggling of antiferromagnetic states is demonstrated in zero magnetic field between 300 and 400K. Various mechanisms including concentration dependent TN-enhancement, voltage-controlled anisotropy, spin-canting, and a Néel spin orbit torque are simultaneously activated.Our results demonstrate that B-doping turns magnetoelectric Cr2O3 into a high-TN, multi-functional material with electrically switchable Néel vector enabling CMOS compatible ultra-low power antiferromagnetic spintronics which operates in zero magnetic field. |
Tuesday, March 3, 2020 12:03PM - 12:15PM |
G47.00005: Voltage Controlled Anisotropy in Boron-doped Cr2O3 thin films Will Echtenkamp, Ather Mahmood, Christian Binek Voltage controlled magnetization is a promising route for next-generation low-energy magnetic recording and logic devices. Utilizing magnetoelectric chromia (Cr2O3) based heterostructures, electric control of ferromagnetic exchange bias has been achieved up to the bulk Néel temperature of 307 K. Recently, it has been shown the Néel temperature of chromia can be increased to 400 K by boron doping. Moreover, boron doping could also introduce spin canting and enhance voltage controlled anisotropy which has been predicted in pure chromia, transforming B-doped chromia into a high-TN multi-functional material. Here the spin flop transition of chromia is investigated and inferences about the crystal anisotropy are drawn. Utilizing low-temperature spin-flop magnetic measurements in B-doped chromia thin films, voltage controlled anisotropy is investigated for the first time in these films, with significant implications for future spintronic devices. |
Tuesday, March 3, 2020 12:15PM - 12:27PM |
G47.00006: Antiferromagnetic Domain Dynamics in Nickelate Heteorstructures Sangjae Lee, Juan Jiang, Gilberto F L Fabbris, Claudio Mazzoli, Ankit Disa, Mark Dean, Frederick J Walker, Charles H Ahn Understanding the energetics of the antiferromagnetic (AF) domains and the timescale of their fluctuations in a magnetic material are important for its application in spin-based electronics. NdNiO3 (NNO) undergoes an AF transition at ~150K, and thus it serves as an oxide platform to study and engineer its AF ground state. We investigate how dimensional confinement leads to phase fluctuations in atomically layered (NdNiO3)m/(NdAlO3)n heterostructures through x-ray photon correlation spectroscopy (XPCS). The speckle patterns arising from coherent x-ray scattering provide the information on long- and short- ranged correlations for different heterostructures with varying thickness of nickelate layers, m, and aluminate layers, n. We find that the dynamics of the AF domain boundaries are dramatically enhanced as the dimensionality of the NNO layers are reduced, approaching the 2D limit. The dynamics of AF domain fluctuations in the heterostructure can be further tailored by tuning the interlayer coupling of nickelate layers. Our study demonstrates a path to characterize any long-range orders in quantum materials under dimensional effect and enables us to control AF domain configurations in oxide heterostructures. |
Tuesday, March 3, 2020 12:27PM - 1:03PM |
G47.00007: Spin transport in antiferromagnetic insulators: progress and challenges Invited Speaker: Dazhi Hou Spin transport is the key process for the operation of spin-based devices, which has been the focus of the spintronics research in the last two decades. Conductive materials such as semiconductors and metals, in which the spin transport relies on electron diffusion, were employed as the channels for spin transport in most studies. Due to the absence of conduction electron, insulators were excluded from the candidates for spin current channel before 2010. However, since the demonstration of the spin transmission through ferromagnetic insulator, it was realized that insulators with magnetic ordering can also serve as channels for spin transport[1]. In this talk I would like to introduce our recent progress of spin transport in antiferromagnetic insulators, e.g., the observations of temperature dependence of spin transmission, and spin current switching[2,3]. I would like to discuss the challenges for developing the functionality of antiferromagnetic insulator as well[4]. |
Tuesday, March 3, 2020 1:03PM - 1:15PM |
G47.00008: Spin Transport in Multiferroic BiFeO3 thin films Hongrui Zhang, Xiaoxi Huang, Yen-Lin Huang, Ramamoorthy Ramesh Creation, detection, manipulation of spin current are the core issues in the spintronics field. In general, spin current can be manipulated by tuning charge current. BiFeO3 is a multiferroic material, which has a strong magneto-electric coupling. We study spin-current transmission in La-doped BiFeO3 (LBFO) thin films by using a trilayer device that sandwiches a LBFO thin film between a magnetic CoFe and a strong spin orbit coupling SrRuO3 layer. Spin current transmission in LBFO thin films can be controlled by the electric field and La-doping concentration through changing antiferromagnetic spin orientation. The control of pure spin current by multiferroic materials may provide a new route towards next-generation electronics. |
Tuesday, March 3, 2020 1:15PM - 1:27PM |
G47.00009: Unleashing antiferromagnetic fluctuations for charge and spin responses of pseudo-spin-half square-lattice Lin Hao, Junyi Yang, Han Zhang, Derek Meyers, Hidemaro Suwa, Zhentao Wang, Mark Dean, Cristian Batista, Jian Liu While manipulation of antiferromagnetic (AFM) order arises to the forefront of spintronics, it is a long-standing fundamental problem lying at the heart of correlated electron physics. Here we will present a series of exciting findings in pseudo-spin-half square-lattice systems, which are implemented as artificial layered iridates [(SrIrO3)1/(SrTiO3)m] to engage with a staggered magnetic field effect (STMF) due to strong spin-orbit interaction. By tuning the SrTiO3 spacer, the AFM structure of the Mott insulating state can be engineered [Phys. Rev. Lett. 119, 027204 (2017)]. With m = 1, the STMF leads to an intriguing positive anomalous magnetoresistance that probes the AFM susceptibility, because of the strong interplay between charge and longitudinal spin fluctuations [Nat. Commun. Accepted (2019)]. Upon driving the AFM structure to the two-dimensional limit at m = 2, while the ordering temperature is significantly reduced by strong critical fluctuations, the STMF allows an external field of only a thousandth of the superexchange interaction to greatly suppress the AFM fluctuations and enable a giant response of the AFM order [Nat. Phys. 14, 806 (2018)]. |
Tuesday, March 3, 2020 1:27PM - 1:39PM |
G47.00010: Intrinsic Exchange Bias in Epitaxial CoFe2O4 thin film Detian Yang, Xiaoshan Xu, Yu Yun Exchange bias (EB), traditionally known as an interface phenomenon between ferro- or ferrimagnetic (FM) materials and antiferromagnetic (AFM) materials, has been successfully applied in magnetic storage and spintronic devices. Recently, surprising “intrinsic” EB (IEB) effects without a nominal AFM layer have drawn much attention. To ascertain the mechanism of IEB, we grew CoFe2O4 thin films epitaxially on sapphire (0001) substrates by pulsed laser deposition and studied its magnetometry by superconducting quantum interference device. In this single film, magnetization loops indicate the coexistence of a soft and a hard FM component, while the observed EB effect ---their clear shifts from the origin, suggest the existence of another AFM component. Analyses based on Preisach model demonstrate that only the hard FM component contributes to the EB. Thickness and temperature dependent EB and coercivity signatures are also extracted from these triple-component hysteresis loops. Our experiment suggests a potential application of adjustable EB and provide new platforms to study the elusive mechanism of intrinsic EB. |
Tuesday, March 3, 2020 1:39PM - 1:51PM |
G47.00011: Fabrication of GeNi2O4, GeCu2O4, and MgCr2O4 Epitaxial Thin Films Fangdi Wen, Denis Vasiukov, Mikhail Kareev, Xiaoran Liu, Liang Wu, Padraic Shafer, Elke Arenholtz, Jak Chakhalian In the AB2O4 spinel system with B site magnetic, a rich variety of magnetic and orbital frustration has been observed. Highlighted phenomenons like spin-liquid phase and field-induced novel phase transitions were seen in these single-crystal systems extensively. Here we report on the first growth of the (001)-oriented GeNi2O4, (001)-oriented GeCu2O4 and (111)-oriented MgCr2O4. All fabricated films were characterized by X-ray diffraction and X-ray photoelectron spectroscopies confirming both crystalline epitaxy and chemical stoichiometry. Synchrotron-based X-ray absorption spectroscopies were also carried out to prove the correct electronic state. The availability of single-crystalline thin films can pave the road to understand the magnetic ordering of differently-oriented spinels in an ultra-thin limit. |
Tuesday, March 3, 2020 1:51PM - 2:03PM |
G47.00012: Designing complex exchange interaction pathways in spinel films using entropy stabilization Thomas Zac Ward, Alessandro Mazza, Brianna Musico, Elizabeth Skoropata, Yogesh Sharma, Wenrui Zhang Magnetic behaviors in AB2O4 spinels are dictated by the magnetic exchange interactions within and between the tetrahedral and octahedral sublattices. Functionality is then tied directly to the distribution and type of cations present within the unit cell. We will present our recent work developing entropic stabilization to synthesize single-crystal high entropy spinel oxide films of the AB2O4 type, where the cation sites are populated by 5 or more elements. We will describe how cation selection can be used to modify the type and strength of exchange interactions present in the crystal lattice. Lab-scale magnetic and structural characterization combined with beamline-based x-ray spectroscopy and neutron diffraction demonstrate the presence of highly tunable and varied magnetic responses; including: room temperature ferrimagnetic insulating states, surface-stabilized spin textures, tunable compensation points, and extraordinarily high strain-induced magnetic anisotropy. |
Tuesday, March 3, 2020 2:03PM - 2:15PM |
G47.00013: Tunable electronic and magnetic properties in Eu1-xLaxTiO3 (0< x <1) Hyungki Shin, Bruce Davidson, Fengmiao Li, Chong Liu, Ronny Sutarto, Ke Zou We explore the magnetic transitions and electronic structures of strained Eu1-xLaxTiO3 (0<x<1) grown by oxide molecular beam epitaxy (MBE). In bulk, undoped EuTiO3 (Ti4+) is insulating and antiferromagnetic with a Néel temperature of ~ 5.5 K, while LaTiO3 (Ti3+) is a Mott insulator with a Néel temperature of ~ 160K. Previous experiments of doping EuTiO3 or LaTiO3 thin films show novel emergent states, such as ferromagnetism, skyrmions, and metal-insulator transition. We show the studies of high-quality thin films of Eu1-xLaxTiO3 from x = 0 to x = 1. With a different ratio of Eu2+/La3+, we observe a series of transitions in the films. We will complete the phase diagram of this system. |
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