United States

Authors: A. Solyom, M. Caouette-Mansour, B. Ruffolo, L. Childress, J. Sankey, Physics, McGill University, Montreal, Quebec, CANADA|P.M. Braganca, Western Digital Corp, San Jose, California, UNITED STATES|M. Pioro-Ladrière, Institut Quantique and Département de Physique, Universite de Sherbrooke, Sherbrooke, Quebec, CANADA|M. Pioro-Ladrière, Quantum Information Science Program, Canadian Institute for Advanced Research, Toronto, Ontario, CANADA|

Abstract Body: We discuss our latest efforts toward using a single, optically active nitrogen-vacancy (NV) spin sensor (implanted in a single-crystal diamond substrate) to measure magnetic thermal noise modified by spin Hall torques [1] in a Py/Pt nanowire [2]. In this poster, we first present our subtractive method for fabricating magnetic nanocircuits on diamond, and initial characterization of working Py(5 nm)/Pt(5 nm) nanowires. We reliably achieve contacts with few-ohms of resistance and 200 nm of overlap at each end of the 2-μm-long, 400-nm-wide wire, and we observe an anisotropic magnetoresistance of 0.4%. Importantly, we observe that the subtractive patterning process (masked ion milling) used to define the devices reduces the NV spin resonance contrast by a factor of ∼5, but that subsequent exposure to an oxygen plasma returned the contrast to its nominal level without affecting the nanowire behavior. Finally, we present progress toward using transport measurements to estimate thermal time scales in these systems (while calibrating the RF current in the nanowire), as well as preliminary NV readout of spin-transfer-controlled magnetic thermal noise.References: [1] C. Du, T. van der Sar, et al., Science, 357, 195-198 (2017) [2] A. Solyom, Z. Flansberry, et al., Nano Lett., 18, 6494-6499 (2018)

MMM 2020

GMW Best Poster Award 2 - Sensing Stray Fields From Magnetic Nanocircuits With Nitrogen-Vacancy Defects

The 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) was held in a virtual form. The COVID-19 pandemic, with its associated uncertainty about international travel and the ability to gather in large groups, meant that the Steering Committee decided to cancel the face-to-face meeting that had been planned in Palm Beach, Florida November 2-6, 2020.

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poster

Weyl Semimetals for Spintronics

Advanced Static and Dynamic Spin Depth Profiling

Magnetic Nanoparticles for Biomedical Diagnostics and Imaging: Recent Advances and Perspectives

 Antiferromagnetic Sprintronics: Transport and Dynamics in Metals, Insulators, and Magnetic Tunnel Junctions

Physics and Applications in Transmission and Control of Spin-Orbit Torques

Next Generation Artificial Spin Ice

New Approaches for Information Processing Coupling Spintronics and Magnonics

Novel Approaches to the Excitation and Control of Nano-Scale Propagating Spin Waves 

Modern spintronic based devices, such as magnetic random-access memories and magnetic read head sensors have been designed on the principles of exchange bias effect [1]. A unidirectional interfacial exchange coupling between a ferromagnet (FM) and an antiferromagnet (AFM) is the primary reason for the shift of field-cooled hysteresis loop leading to the exchange bias effect [2]. Other prominent signatures of exchange bias are enhancement of coercivity and observation of training effect. This phenomenon is generally interfacial in origin, however sometimes spins from the ‘bulk’ part of the AFM can also contribute to exchange bias [3]. Besides, the interface can be ferromagnetic, antiferromagnetic or spin-glass in nature. Interestingly, all the above features are system dependent and can vary with the thickness of the films.
 
We have investigated the role of ‘bulk’ spins of the AFM and also explored the magnetic nature of interface in exchange coupled Fe/IrMn bilayers by varying the thickness of the IrMn layer. In contrast with the conventional FM/AFM exchange bias systems [4], the exchange bias field (HEB) was found to decrease with increasing cooling field (HFC) due to random interface effect [2, 5]. The analysis of the training effect data indicates the presence of frozen and rotatable interfacial spins that contributed to the observed loop shift and coercivity enhancement, respectively.

 
References: [1] K. O’Grady, S. J. Greaves, S. M. Thompson, J. Magn. Magn. Mater., 322, 883 (2010)

[2] K. D. Usadel, U. Nowak, Phys. Rev. B, 80, 014418 (2009)

[3] A. C. Basaran, T. Saerbeck, J. de la Venta, H. Huckfeldt, A. Ehresmann, Ivan K. Schuller Appl. Phys. Lett., 105, 072403 (2014)

[4] L. D. Bianco, F.Spizzo, M.Tamisari, S.Laureti, Solid State Commun., 151, 351 (2011)

[5] S. Nayak, P. K. Manna, V. Thiruvengadam, B. B. Singh, S. Bedanta, J. Magn. Magn. Mater., 499, 166267 (2020)

Exchange bias in Fe/Ir20Mn80 bilayers: role of spin-glass like interface and ‘bulk’ antiferromagnet spins

Topological spin textures, such as skyrmions, have attracted intense interest in recent years. Magnetic skyrmions have been studied almost exclusively in bulk ferromagnets (FM) or FM multilayers. Antiferromagnets (AF) have also been predicted to harbor topological spin textures such as AF skyrmions. Topological Hall effect has been a primary indicator of spin textures in magnetic materials. We observe unambiguous evidence of topological Hall effect in Pt/Cr2O3 bilayers grown on Al2O3(0001) and Al2O3(11-20), where Cr2O3 epitaxial film is an antiferromagnetic insulator[1]. Although Cr2O3 is insulating, the topological magnetic textures can be detected through a novel phenomenon: “spin-Hall topological Hall effect” (SH-THE), similar to what recently observed topological Hall effect in Pt/Tm3Fe5O12 bilayers[2]. The Pt/Cr2O3 bilayers exhibit clear topological Hall resistivity for Cr2O3 thicknesses below 6 nm near and above room temperature, which is above the Néel temperature of Cr2O3, revealing the key role of thermal fluctuations in the formation of spin textures[3]. The similarity of topological Hall signals in (0001) and (11-20)-oriented Cr2O3 films indicates that the emergence of spin textures is insensitive to crystalline orientation. This first observational evidence of topological Hall effect in HM/AFI bilayers significantly expands our materials base to include the large family of AF insulators for the exploration of AF-based skyrmion technology.References: [1]. Yang Cheng, Sisheng Yu, Menglin Zhu, Jinwoo Hwang and Fengyuan Yang, “Evidence of Topological Hall Effect in Pt/Antiferromagnetic-Insulator Bilayers,” Phys. Rev. Lett. 123, 237206. [2]. A. S. Ahmed, A. J. Lee, N. Bagués, B. A. McCullian, A. M. A. Thabt, A. Perrine, P.-K. Wu, J. R. Rowland, M. Randeria, P. C. Hammel, D. W. McComb, and F.. Y. Yang, “Spin-Hall topological Hall effect in highly tunable Pt/ferrimagnetic-insulator bilayers,” Nano Lett., 19, 5683 (2019). [3]. Wenbo Wang, Matthew W Daniels, Zhaoliang Liao, Yifan Zhao, Jun Wang, Gertjan Koster, Guus Rijnders, Cui-Zu Chang, Di Xiao and Weida Wu, "Spin chirality fluctuation in two-dimensional ferromagnets with perpendicular magnetic anisotropy" Nat. Mater. 2019, 18, 1054.

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