The influence of an electric field on an ultrathin FeCo film was investigated by x-ray absorption spectroscopy and magnetic circular dichroism. Measurements were done on sub-millimeter sized pillars, with partial fluorescence yield detection. Fe L2,3 absorption spectra revealed that partial oxidation of Fe occurred during the microfabrication. The oxidation state could be reversibly controlled by an electric field, which also induced variations of the dichroic signal. These results show that electrochemical phenomena may influence the magnetism at a ferromagnet/insulator interface.

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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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.

We investigated spin-dependent quantum interference effects in Cr(001)/wedge Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions by dI/dV measurements. dI/dV intensities were mapped two-dimensionally as a function of applied voltage and Fe thickness, indicating a clear signature of quantum well (QW) states in the ultrathin Fe (001) electrode. However, resonant positions of QW states were systematically shifted by one monolayer when compared with the first-principles calculation results. X-ray absorption spectroscopy and magnetic circular dichroism measurements were also performed. While Fe oxide presence at Fe/MgO interface was ruled out, Fe/Cr intermixing could not be excluded. Hence, controlling the Fe/Cr interface may affect QW state.

Effects of grain cluster size on coercivity and giant magnetoresistance of NiFe/Cu/CoFe/Cu/NiFe pseudo spin valves Appl.We present measurements of magneto-Seebeck effect on a spin valve with in-plane thermal gradient. We measured open circuit voltage and short circuit current by applying a temperature gradient across a spin valve stack, where one of the ferromagnetic layers is pinned. We found a clear hysteresis in these two quantities as a function of magnetic field. From these measurements, the magneto-Seebeck effect was found to be same as magneto-resistance effect. C 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx.

Magnetic tunnel junctions (MTJs) have been identified as promising candidates for the development of high-performance, ultra-low field magnetometers due to their high sensitivity, low cost, low power consumption, and small size. However, 1/f noise is often quite large at low frequencies and inevitably becomes one of the most difficult issues in developing a magnetic field sensor with ultrahigh sensitivity. Low-frequency 1/f noise can have both electric and magnetic origins, and it is a result of complex non-linear interactions between many degrees of freedom inside a sensor. Therefore, a reduction of the 1/f noise can be expected for the magnetic sensor with very small dimensions. Here, the dependence of the 1/f noise on voltage and strong hard-axis bias field in deep submicrometer-sized MgO-based MTJs is investigated with various junction sizes. The noise spectra were measured by using a home-built low-frequency noise measurement setup with maximum frequency up to 30 kHz. We find that the noise spectral power density is 1/f-like at low frequencies. The experimental results suggest a relative reduction of 1/f noise with respect to the intrinsic thermal noise in small-sized MTJs. The results may open a new approach for reducing the 1/f noise level in MTJ nanosensors.

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