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...

Generation of spin current lies at the heart of spintronic research. The spin Hall effect and the spin Seebeck effect have drawn considerable attention in the last few years to create pure spin current by heavy metals and ferromagnets, respectively. In this work, we show the direct evidence of heat current to spin current conversion in non-magnetic Platinum by the spin Nernst effect (SNE) at room temperature. This is the thermal analogue of the spin Hall effect in non-magnets. We have shown that the 8 K/μm thermal gradient in Pt can lead to the generation of pure spin current density of the order of 108 A/m2 by virtue of SNE. This opens up an additional possibility to couple the relativistic spin-orbit interaction with the thermal gradient for spintronic applications.

A gyrator is a non-reciprocal two port device with 180° phase shift in the transmissions between two ports. Though electromagnetic realizations of gyrators have been well studied, devices based on other forms of interaction are relatively unexplored. Here we demonstrate a device in which signal is transmitted via magneto-elastic coupling, can function as a gyrator. The device is built on a piezoelectric substrate: one port of this device has interdigital transducers (IDTs) and the other port has a periodic array of nickel/gold lines. When the magnetizations of Ni lines are excited into precession by magnetic field generated by passing oscillating current through the gold lines, they emit phonons in the form of surface acoustic waves (SAW) due to the magneto-elastic coupling between Ni and substrate. The emitted SAW can be detected at the other end by the IDTs. Conversely, when SAW is incident on Ni lines from IDTs, the magnetization undergoes precession and can be inductively detected by Au lines. The broken time reversal symmetry of the system due to the presence of ferromagnet gives rise to the non-reciprocal transmission between the two ports. These devices could function as novel building blocks for phonon based information processing.

Relativistically originated spin-orbit torque is one of the promising ways to control magnetization dynamics of ferromagnet which can be useful for next generation spintronic memory applications. Lot of effort has been made to address the physical origin of spin-orbit torque and improve its efficiency. In this work we demonstrate that in ultrathin chromium /Nickel (Cr/Ni) hetero-structure, spin-orbit torque significantly increases for Cr thickness below 6 nm. We have also observed unconventional sign of field like torque which can be attributed to the interfacial Rashba kind of coupling. We experimentally obtain that approximately 35 Oe Rashba kind of magnetic field is created on 8 nm thick in-plane magnetized Ni film when 10 8 A/cm 2 current density flows through Cr layer.

We report the thermally driven giant field-like spin-torque in magnetic tunnel junctions (MTJ) on application of heat current from top to bottom. The field-like term is detected by the shift of the magneto-resistance hysteresis loop applying temperature gradient. We observed that the field-like term depends on the magnetic symmetry of the MTJ. In asymmetric structures, with different ferromagnetic materials for free and fixed layers, the field-like term is greatly enhanced. Our results show that a pure spin current density of the order of 109 A/m2 can be produced by creating a 120 mK temperature difference across 0.9 nm thick MgO tunnelling barrier. Our results will be useful for writing MTJ and domain wall-based memories using thermally driven spin torque.