Unidirectional magnetoresistance (UMR) has been observed in a variety of stacks with ferromagnetic/spin Hall material bilayer structures. In this work, UMR in antiferromagnetic insulator Fe2O3/Pt structure is reported. The UMR has a negative value, which is related to interfacial Rashba coupling and band splitting. Thickness‐dependent measurement reveals a potential competition between UMR and the unidirectional spin Hall magnetoresistance (USMR). This work reveals the existence of UMR in antiferromagnetic insulators/heavy metal bilayers and broadens the way for the application of antiferromagnet‐based spintronic devices.
Origins of observational errors in field sweep DC measurements for unidirectional magnetoresistance
Understanding the mechanisms of unidirectional magnetoresistance (UMR) has become an important topic for its potential application of a two-terminal spin–orbit torque device. Field sweep DC measurements have been proposed and adopted to measure the value of UMR instead of second harmonic measurements. In this paper, potential measurement errors in conventional DC measurements are investigated. Oersted field and field-like torque usually do not influence the measurement, but a large field-like torque was found to lead to an anisotropic magnetoresistance difference when the sample is not perfectly aligned with the external field. The existence of ordinary magnetoresistance was also found to contribute to a large background. In this paper, an alternative measurement method for UMR was proposed and demonstrated to address those issues related to previous DC measurements. Our work may broaden the understanding of the error sources of UMR measurements and provide a reliable DC measurement method for the characterization of UMR.
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- Award ID(s):
- 2011401
- NSF-PAR ID:
- 10411308
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 132
- Issue:
- 21
- ISSN:
- 0021-8979
- Page Range / eLocation ID:
- 213907
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
Unidirectional spin Hall magnetoresistance (USMR) is a magnetoresistance effect with potential applications to read two-terminal spin–orbit-torque (SOT) devices directly. In this work, we observed a large USMR value (up to 0.7 × 10 −11 per A/cm 2 , 50% larger than reported values from heavy metals) in sputtered amorphous PtSn 4 /CoFeB bilayers. Ta/CoFeB bilayers with interfacial MgO insertion layers are deposited as control samples. The control experiments show that increasing the interfacial resistance can increase the USMR value, which is the case in PtSn 4 /CoFeB bilayers. The observation of a large USMR value in an amorphous spin–orbit-torque material has provided an alternative pathway for USMR application in two-terminal SOT devices.more » « less
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It was recently demonstrated in bilayers of permalloy and platinum, that by combining spin torques arising from the spin Hall effect with Oersted field-like torques, magnetization dynamics can be induced with a directional preference.1 This “unidirectional” magnetization dynamic effect is made possible by exploiting the different even and odd symmetry that damping-like and field-like torques respectively have when magnetization is reversed. The experimental method used to demonstrate this effect was the spin-torque ferromagnetic (ST-FMR) resonance technique; a popular tool used in the phenomenological quantification of a myriad of damping-like and field-like torques. In this report, we review the phenomenology which is used to describe and analyze the unidirectional magnetization dynamic effect in ST-FMR measurements. We will focus on how the asymmetry in the dynamics also is present in the phase angle of the magnetization precession. We conclude by demonstrating a utility of this directional effect; we will outline an improved experimental method that can be used to distinguish a phase-shifted field-like torque in a ST-FMR experiment from a combination of field-like and damping-like torques.more » « less
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Despite Uniform Meaning Representation’s (UMR) potential for cross-lingual semantics, limited annotated data has hindered its adoption. There are large datasets of English AMRs (Abstract Meaning Representations), but the process of converting AMR graphs to UMR graphs is non-trivial. In this paper we address a complex piece of that conversion process, namely cases where one AMR role can be mapped to multiple UMR roles through a non-deterministic process. We propose a neuro-symbolic method for role conversion, integrating animacy parsing and logic rules to guide a neural network, and minimizing human intervention. On test data, the model achieves promising accuracy, highlighting its potential to accelerate AMR-to-UMR conversion. Future work includes expanding animacy parsing, incorporating human feedback, and applying the method to broader aspects of conversion. This research demonstrates the benefits of combining symbolic and neural approaches for complex semantic tasks.more » « less
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Calzolari, Nicoletta ; Kan, Min-Yen ; Hoste, Veronique ; Lenci, Alessandro ; Sakti, Sakriani ; Xue, Nianwen (Ed.)Uniform Meaning Representation (UMR) is a semantic labeling system in the AMR family designed to be uniformly applicable to typologically diverse languages. The UMR labeling system is quite thorough and can be time-consuming to execute, especially if annotators are starting from scratch. In this paper, we focus on methods for bootstrapping UMR annotations for a given language from existing resources, and specifically from typical products of language documentation work, such as lexical databases and interlinear glossed text (IGT). Using Arapaho as our test case, we present and evaluate a bootstrapping process that automatically generates UMR subgraphs from IGT. Additionally, we describe and evaluate a method for bootstrapping valency lexicon entries from lexical databases for both the target language and English. We are able to generate enough basic structure in UMR graphs from the existing Arapaho interlinearized texts to automate UMR labeling to a significant extent. Our method thus has the potential to streamline the process of building meaning representations for new languages without existing large-scale computational resources.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0127587
