Magneto-Seebeck effect in spin-valve with in-plane thermal gradient

Jain, Sourabh; Lam, D. D.; Bose, Arnab; Sharma, Himanshu; Palkar, V. R.; Tomy, C. V.; Suzuki, Y.; Tulapurkar, Ashwin

doi:10.1063/1.4905137

Cited by 14 publications

(10 citation statements)

References 32 publications

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“…Resistance of the sample depends on the mutual orientation of magnetization between free and fixed layer ( Fig. 1d) which originates from current in-plane GMR effect 21 . Clear GMR hysteresis is observed ( Fig.…”

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confidence: 99%

“…These torques can be attributed to either Slonczewski's spin-transfer torque (STT) 13 or field-like torque (FLT) 3,8,14 . STT arises when ferromagnet absorbs spin current generated by many ways like spin-Hall effect (SHE) 15,16 , spin-pumping 17 , spin-Nernst effect 18 , spin-(dependent) Seebeck effect [19][20][21] etc. Field-like torque is generally observed in asymmetric magnetic tunnel junctions (MTJ) with current perpendicular to the plane (CPP) geometry 3,14,22 and ferromagnet/heavy metal bilayer where Rashba 8 or Dressulhous 7 spin orbit interaction is present.…”

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Observation of Anomalous Spin Torque Generated by a Ferromagnet

et al. 2018

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Over the years central research of spintronics has focused on generating spin-current to manipulate nano-magnets by spin torque. So far electrically 1-9 and thermally driven spin-torques [10][11][12] have been experimentally demonstrated. These torques can be attributed to either Slonczewski's spin-transfer torque (STT) 13 or field-like torque (FLT) 3,8,14 . STT arises when ferromagnet absorbs spin current generated by many ways like spin-Hall effect (SHE) 15,16 , spin-pumping 17 , spin-Nernst effect 18 , spin-(dependent) Seebeck effect 19-21 etc. Field-like torque is generally observed in asymmetric magnetic tunnel junctions (MTJ) with current perpendicular to the plane (CPP) geometry 3,14,22 and ferromagnet/heavy metal bilayer where Rashba 8 or Dressulhous 7 spin orbit interaction is present. Control of magnetization dynamics is not only interesting from physics perspective but also useful in technological applications 23,24 . We have experimentally observed a new form of spin torque which is completely different from conventional STT and FLT. This unconventional spin torque is exerted by a fixed magnet on a free magnet in spin valve structure with current in-plane (CIP) geometry. The observed spin torque originates from an out of plane effective magnetic field with symmetry of (M× J), where M denotes the magnetization direction of fixed FM and J denotes current density. This torque could be potentially useful for switching out-of-plane magnets in high density MRAM.Spin-orbit torque 4,7,8,25 has evolved in a promising way to manipulate spins since last few years. Heavy metals like Pt 26 , anti-ferromagnets 27,28 , two dimensional materials 29,30 and semiconductor systems 7 have been recently studied as candidates for generating spin torques. However ferromagnetic metal (FM) itself has its own spin-orbit coupling which is responsible for various effects like: anisotropic magneto resistance (AMR), planar Hall effect (PHE) and anomalous Hall effect (AHE). AHE is analogous to SHE in heavy metal which can induce spin current in neighbouring metal and cause spin orbit torque (Fig. 1b). Previous studies show that spin Hall angle of FM 31,32 is quite comparable to Pt. Hence FM can be considered as good candidate for SOT [33][34] . To study spin orbit torque by FM we need FM(free)/Cu/FM(fixed) heterostructure where fixed layer will be source of spin current which will exert torque on another FM separated by Cu spacer. Based on this principle we carried out spin-torque ferromagnetic resonance (ST-FMR) 3,7,26 measurement of current in-plane giant-magnetoresistive (GMR) stack consisting of Ta(5 nm)/Ru(5 nm)/IrMn(7 nm)/CoFe(2 nm)/Cu(5 nm)/CoFe(2 nm)/Cu(5 nm). However we surprisingly observe the existence of a new kind of torque which is completely different from standard spin-orbit torque by FM (owing to its AHE) which we initially expected. This unconventional spin-torque depends on the mutual orientation of fixed layer magnetization direction (M) and direction of in-plane current flow (J) and manifests itself as an effect...

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Observation of Anomalous Spin Torque Generated by a Ferromagnet

et al. 2018

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“…Gravier [12] and Sakurai [13] et al reported a fielddependent thermopower in Fe/Cr and Co/Cu multilayers and they discussed little on physics hidden behind it. Very recently, Jain [14] et al reported a tiny field-dependent Seebeck effect in CoFe/Cu/CoFe/IrMn/Ru spin valves. They further attributed its field dependence to the trivial origin that different resistances in parallel (P) state and antiparallel (AP) state resulted in different Seebeck coefficients accordingly.…”

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Magneto-Seebeck effect in spin valves

Zhang

Wan

et al. 2017

Journal of Applied Physics

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Giant magneto-Seebeck (GMS) effect was observed in Co/Cu/Co and NiFe/Cu/Co spin valves. Their Seebeck coefficients in parallel state was larger than that in antiparallel state, and GMS ratio defined as (SAP-SP)/SP could reach -9% in our case. The GMS originated not only from trivial giant magnetoresistance but also from spin current generated due to spin-polarized thermoelectric conductivity in ferromagnetic materials and subsequent modulation of the spin current by different spin configurations in spin valves. Simple Mott two-channel model reproduced a -11% GMS for the Co/Cu/Co spin valves, qualitatively consistent with our observations. The GMS effect could be applied simultaneously sensing temperature gradient and magnetic field and also be possibly applied to determine spin polarization of thermoelectric conductivity and Seebeck coefficient in ferromagnetic thin films.

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“…Nernst effect gives these materials an advantage for application and increases the usability of these materials in spin-based devices [12,64]. Tremendous research efforts have been devoted in spin caloritronics to investigate the interplay of spin and thermoelectric transport phenomena [1,6,7,8,9]. La 0.7 Sr 0.3 MnO 3 (LSMO) is an important material for spintronics due to its large spin-polarization [3].…”

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confidence: 99%