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The effect of Mn doping of a Cr84Re16 alloy are reported, as well as the possible existence of a spin glass (SG) state which were investigated using electrical resistivity and magnetisation measurements. Mn is an electron donor resulting in a concomitant increase in the size of the electron sheet and a subsequent increase in Néel temperature, TN [1]. The temperature dependence of magnetisation, M(T), for the (Cr84Re16)100−xMnx alloys with x = 0.4, 0.6 and 3.1 showed bifurcation of the M(T) data at the pinning temperature, Tp, in the zero field cooled (ZFC) and field cooled (FC) curves. The splitting of the ZFC and FC curves is not in itself a signature of SG but is an indication of magnetic anisotropy in the system [2]. In the (Cr84Re16)100−xMnx alloy system, there is a sharp increase in magnetisation on increasing T after ZFC. A prominent peak is observed close to 40 K above which the behaviour is identical to that observed in the FC state as shown in the figure for the x = 0.4 alloy. Other signatures associated with canonical SG namely the time dependence of isothermal remanent magnetisation (IRM) and the increase of magnetic stiffness upon increasing the wait time in thermoremanent magnetisation (TRM) were also observed in the (Cr84Re16)100−xMnx alloys [3]. The frequency dependence of the real component of AC-susceptibility shows the SG characteristic cusp close to Tp [4]. However, there is no dependence of the maximum value of cusp or the temperature corresponding to the cusp on frequency which is contrary to the SG state [5]. As only some of the SG signatures were observed in the (Cr84Re16)100−xMnx alloy system, it cannot be categorised as canonical SG. These alloys can be classified as a new type of SG with frustration of itinerant spins at the interfaces between antiferromagnetic (AFM) domains established around each Mn local magnetic moment.References: [1] E. Fawcett, H.L. Alberts, V.Y. Galkin, D.R. Noakes and J.V. Yakhmi, Rev. Mod. Phys., Vol. 66, p.25 (1994) [2] P.A. Joy, P.S. Anil Kumar and S.K. Date, J. Phys. Condens. Matter., Vol. 10, p.11049 (1998) [3] B. Li, H.L. Alberts, A.M. Strydom, B.M. Wu, A.R.E. Prinsloo and Zh.J. Chen, J. Magn. Magn. Mater., Vol. 321, p.61 (2009) [4] C.A.M. Mulder, A.J. Van Duyneveldt and J.A. Mydosh, Phys. Rev. B., Vol. 25, p.515 (1982) [5] J.A. Mydosh, “Spin glasses: an experimental introduction”, Taylor and Francis, London (1993)

MMM 2020

Spin Glass Behaviour in (Cr84Re16)100−xMnx Alloys

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

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)

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

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)

Spin Glass Behaviour in (Cr84Re16)100−xMnx Alloys

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

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