J. Kanak

Influence of buffer layer texture on magnetic and electrical properties of IrMn spin valve magnetic tunnel junctions

Spin valve magnetic tunnel junctions (SV-MTJs) with the structure Si(100)∕SiOx∕buffer(A,B)∕IrMn∕CoFe∕AlOx∕NiFe∕Ta have been deposited on two buffers: Cu (group A) and Ta∕Cu (group B). The A junctions were characterized by a low degree of texture and a small amplitude of roughness, and B junctions by a high degree of texture and a high amplitude of roughness. The strongly textured buffer Ta∕Cu (group B) grew in a columnarlike fashion and induced interfacial roughness. The texture and the roughness modified strongly the interlayer and the exchange bias coupling fields in the SV-MTJs. A substantial influence of the roughness, due to barrier thickness fluctuation, on the resistance area product (R×A) of junctions was also observed. The influence on the temperature dependence of conductance and tunnel magnetoresistance (TMR) was, however, small and only observable at low temperature for the two groups of junctions. A significantly larger increase of the conductance and decrease of the TMR with increasing bias ...

Low resistance magnetic tunnel junctions with MgO wedge barrier

We investigated the dependence of tunnel magnetoresistance (TMR), the resistance area (RA) product, crystallographic structure, the interlayer exchange coupling (IEC) and the coercive (Hc) fields in Co40Fe40B20/MgO/Co40Fe40B20 exchange biased spin valves on the Ar partial pressure, in the range from 1 mTorr to 15 mTorr, during the MgO sputtering. For all the metallic layers a linear dynamic deposition (LDD) with a constant wafer velocity was used, whereas for the MgO deposition a LDD wedge technology with gradient velocity. The crystallographic texture of MgO(001), IEC and Hc fields, TMR and RA significantly depend on the Ar partial pressure. We found that high Ar partial pressure (above 5.6 mTorr) resulted in weaker (001) texture, lower interplanar distances of the MgO barrier and higher IEC field. Low Ar partial pressure gives smoother MgO surfaces and provides good barrier quality which results in higher TMR and RA values

Influence of Interface Roughness, Film Texture, and Magnetic Anisotropy on Exchange Bias in

Co/Pt multilayers can exhibit considerable exchange bias along the film normal when grown onto or covered by an antiferromagnetic IrMn layer. The magnitude of the bias effect depends strongly on the selection of the buffer layers and is largest for Co/Pt multilayers with small perpendicular anisotropy. This counterintuitive result is explained by opposite dependencies of exchange bias and magnetic anisotropy on the degree of film texture and grain size. Interface roughness also influences the perpendicular exchange bias field. The largest biases are measured on smooth films. Interlayer mixing during post-deposition annealing procedures decreases the exchange bias field of IrMn-capped Co/Pt multilayers.

[{\hbox{Pt/Co}}]_{3}/{\hbox{IrMn}}

Two different buffer layers (Ta/Ru/Ta and thick Ta) were tested for MgO MTJs. The influence of buffer layer texture on the crystallization of CoFeB bottom and top electrodes and on the tunnel magnetoresistance effect was investigated. X-ray results suggest that, after anneal, the CoFeB layer above MgO is well (200) textured and it does not depend on the buffer layer since MgO (100) barrier supplies a good template for CoFeB (200) orientation, while the crystallization of bottom CoFeB layer relies on the buffer layer texture. Different from Ta (110) found in Ta/Ru/Ta buffer layer, a thick Ta buffer layer has beta-(200) texture, which induces (001) oriented grains in MnPt layer. Because of the epitaxy relationship between MnPt and FeCo with MnPt(001)[100]//FeCo(200)[110], MnPt (001) oriented grains lead to the crystallization of bottom CoFeB layer with (200) orientation. As a result, higher TMR ratio up to 290% was achieved in the EB-MTJs with thick Ta buffer layer.

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When a current is passed through a non-magnetic metal with strong spin-orbit coupling, an orthogonal spin current is generated. This spin current can be used to switch the magnetization of an adjacent ferromagnetic layer or drive its magnetization into continuous precession. The interface, which is not necessarily sharp, and the crystallographic structure of the nonmagnetic metal can both affect the strength of current-induced spin-orbit torques. Here, we investigate the effects of interface intermixing and film microstructure on spin-orbit torques in perpendicularly magnetized Ta/Co40Fe40B20/MgO trilayers with different Ta layer thickness (5 nm, 10 nm, 15 nm), greater than the spin diffusion length. Effective spin-orbit torques are determined from harmonic Hall voltage measurements performed at temperatures ranging from 20 K to 300 K. We account for the temperature dependence of damping-like and field-like torques by including an additional contribution from the Ta/CoFeB interface in the spin diffusion model. Using this approach, the temperature variations of the spin Hall angle in the Ta underlayer and at the Ta/CoFeB interface are determined separately. Our results indicate an almost temperature-independent spin Hall angle of

Multilayers

{{\boldsymbol{\theta }}}_{{\boldsymbol{SH}}}^{{\boldsymbol{N}}}\approx -{\bf{0.2}}

Influence of intermixing at the Ta/CoFeB interface on spin Hall angle in Ta/CoFeB/MgO heterostructures

θSHN≈−0.2 in Ta and a strongly temperature-dependent