Magnetoresistance and interlayer diffusion in PtMn spin valves upon postdeposition annealing

Abstract

We report annealing time effects on the microstructural evolution and resultant magneto-transport property changes in Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta spin valves comprising PtMn layer thicknesses ranging from 10 to 30 nm. Postdeposition annealing was performed at 270 °C up to 35 h. The blocking temperatures of samples with 20 nm PtMn and 30 nm PtMn layers were found to be 350 °C and 400 °C, respectively. The magnetoresistance and interlayer coupling field changes became large as annealing time increased, in particular, for samples with relatively thicker PtMn layers. The main cause of microstructural changes and property degradation was due to interlayer diffusion of atomic constituents such as Mn, most likely through grain boundaries. Light B doping (1 at. %) in both free and pinned CoFe layers was proven effective in terms of blocking diffusion processes.

The exchange bias of a permalloy and ordered structure of epitaxial PtMn prepared from the growth of thin (Pt/Mn) multilayers

“…After the MBE growth, these samples were then annealed at 250 1C for 1-9 annealing cycles (each cycle for 3 h) under a magnetic field of $650 Oe. The annealing temperature was lower than that of the works of Kim et al [4] and Morales et al [5] situ characterized by the reflection high-energy electron diffraction (RHEED). The crystal structures and order parameters of the films along out-of-plane and in-plane directions were studied by X-ray diffraction (XRD), grazing incidence XRD and X-ray reflectivity at BL17B beamline of National Synchrotron Radiation Research Center (NSRRC) in Taiwan.…”

“…Typically, the antiferromagnetic phase of the PtMn usually requires a post-deposition annealing to convert its crystal structure from a chemically disordered FCC to an ordered face-centered-tetragonal (FCT, L1 0 ) structure, which is essential to achieve a high exchange biasing field (H ex ) [1][2][3][4][5][6]. To understand the mechanism of exchange bias, the quantitative correlation between H ex and the FCT structure of PtMn-related magnetic heterostructures has to be established.…”

Composition dependence of exchange anisotropy in Pt x Mn1−x /Co70Fe30 films

“…19,20) The EB for PtMn is over 450 (Oe) and the blocking temperature of PtMn is over 380 °C according to the previous reports. 21,22) The surface roughness of PtMn is approximately 0.3 nm, which depends on PtMn thickness and annealing temperature, and is much flatter than other Mnbased alloys. 23) PtMn near 1:1 composition does not show antiferromagnetic behavior in as-deposited films, and it has a chemically disordered FCC phase.…”

Comparison on the structure and exchange bias in Co/MnPt and MnPt/Co polycrystalline films on glass substrates

“…L1 0 -Mn 50 Pt 50 is an AF material and has been attracted much attention for EB system due to high Neel temperature (T N = 975 K), large K AF of 1.4 × 10 7 erg/cm 3 , good thermal stability, and especially excellent corrosion resistance. [3][4][5][6][7][8][9][10][11][12][13][14][15] However, the structure of Mn 50 Pt 50 films deposited at room temperature (RT) is paramagnetic disordered face-centered-cubic (FCC) structure and no exchange coupling at interface is induced. In order to form AF ordering and build up strong exchange coupling effect to adjacent FM layers, a thermal process of post annealing and cooling in external magnetic field to RT is essential to form highly ordered L1 0 phase and good AF alignment.…”