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Highlights • Effect of thermal annealing on FeCoNbB thin film having different thicknesses has been studied. • UMA gradually decreases with annealing and disappears upon annealing at 773 K. • Growth induced anisotropic tensile stresses as the possible origin of observed UMA. • Nb addition improves thermal stability, inhibits grain growth and stabilises bcc-FeCo phase. • FeCoNbB films are proposed as potential material for magnetic electrode in MTJ applications. Abstract Influence of thermal annealing on the ion beam sputtered FeCo(Nb)B quaternary alloy thin films having thickness ∼20 nm and 80 nm was investigated. Regardless of amorphous microstructure, the as-deposited films possess uniaxial magnetic anisotropy (UMA) in the film plane. Annealing at temperature ∼503 K results in amorphous to nanocrystalline phase transformation with precipitation of bcc-FeCo phase. With increasing annealing temperature, magnetic anisotropy gradually decreases and thermal annealing at 773 K results in complete disappearance of UMA. In-plane strain distribution in such nanocrystalline FeCo(Nb)B thin films was obtained by using laboratory and synchrotron X-ray diffraction (XRD) measurements. In-plane and out-of-plane X-ray diffraction measurements suggest, growth induced long range non-uniform tensile stress, as the possible origin of in-plane uniaxial magnetic anisotropy in such films. It is demonstrated that the stress distribution becomes uniform after annealing at 773 K and results in complete disappearance of magnetic anisotropy. The study further suggests that the presence of Nb in FeCoB film improves the thermal stability, inhibits grain growth and stabilizes bcc-FeCo phase up to elevated temperatures. This information is useful for magnetic tunnel junction application, where annealing of FeCoB magnetic electrode is essential. [ABSTRACT FROM AUTHOR]

• Polycrystalline Cr/Ni bilayer thin films are fabricated using electron beam evaporation technique. • Room temperature exchange bias is established in polycrystalline Cr/Ni bilayer thin films. • The maximum exchange bias field ∼ 320 Oe was obtained at Ni layer thickness ∼ 8.5 nm at room temperature. • These bilayers exhibit negative exchange bias behavior at ∼ 5 K when subjected to the field cooled (∼1 KOe) protocol. • An oscillatory behaviour of exchange bias with respect to increase in temperature is observed for polycrystalline Cr layer. The phenomenon of negative exchange bias is typically observed in ferromagnetic and antiferromagnetic materials following a field cooling protocol. However, the occurrence of positive exchange bias is hardly found. The majority of models show positive exchange bias after undergoing field cooling or zero-field-cooling process. In this work, we achieved a novel positive exchange bias effect for Cr/Ni bilayer after gradually increasing the temperature from low temperature (5 K) to high temperature (up to RT) in the absence of magnetic field. The M−H loops at different temperatures reveal not only temperature dependent exchange bias but also thickness dependent exchange bias for Cr/Ni layer. A systematic investigation was conducted to analyse the influence of the exchange bias field on the thickness of the ferromagnetic layer. Significantly, our experimental observations also reveal a notable room temperature exchange bias field measuring 320 Oe for the optimum bilayer. Moreover, to obtain a detailed understanding of coercivity in the Cr/Ni bilayer, Kerr hysteresis was also recorded at room temperature in longitudinal geometry (L-MOKE). Hence, the discovery of our work not only suggests a novel methodology to achieve positive exchange bias in ferromagnetic and antiferromagnetic bilayers but also the oscillatory behavior of H EB with respect to increase in temperature is observed for polycrystalline Cr (AFM) layer. [ABSTRACT FROM AUTHOR]

In this work, a series of Fe 4 N thin films with thickness t = 10, 30, 60, and 120 nm were deposited using a reactive dc magnetron sputtering and studied for their structural and the magnetic properties. X-ray diffraction measurements confirmed the formation of a single-phase Fe 4 N and the grain size was found to increase up to t = 60 nm. Magnetization measurements were carried out using the bulk magnetization as well as element-specific magnetic circular dichroism. It was found that the saturation magnetization (M s) maximizes at t = 30 nm. To correlate the observed variation in the M s , we studied the local structure using near edge and extended X-ray absorption fine structure analysis. The effect of local structure and interatomic distances on the magnetic properties of Fe 4 N films have been explored and discussed. • Fe 4 N films of different thicknesses were deposited using magnetron sputtering. • XMCD and SVSM measurements showed a similar trend of magnetization variation with the thickness of the film. • XANES and EXAFS studies revealed local structure variations in the films. [ABSTRACT FROM AUTHOR]

The effect of substrate induced strain and Fe/Rh stoichiometry on the antiferromagnetic (AFM)-ferromagnetic (FM) first order transition in sputter deposited FeRh thin films has been studied. Fe 1 − x Rh x films of about 50 nm thickness and with x = 0.45, 0.50, 0.55 were deposited using magnetron sputtering on MgO (001), Al 2 O 3 (0001) (AlO) and quartz (Qtz) substrates. These films were found to be epitaxial under compressive strain on MgO and polycrystalline under tensile strain on AlO. Films with x = 0.50 and 0.55 showed a first order AFM-FM transition near or above 300 K. Our study shows that the transition temperature (T t) is dictated by strain as it was found to vary linearly with out-of-plane strain for films on MgO and AlO. In the case of films on Qtz substrate, an open loop in isothermal magnetoresistance (MR) with a large negative MR was observed at room temperature. • FeRh thin films (∼ 50 nm) were prepared using dc-magnetron sputtering with varying Fe/Rh composition on MgO (001), Al 2 O 3 (0001) and quartz substrate. • The films on MgO(001) substrate were found to be epitaxial with compressive strain whereas, films on other two substrates turn out to be polycrystalline. • The study shows that the transition temperature of film Fe 0.5 Rh 0.5 and Fe 0.45 Rh 0.55 on MgO and AlO substrate varies linear with substrate induced strain. • The films on quartz substrate showed large negative magnetoresistance (MR) at room temperature due to field induced antiferro–ferromagnetic transition. • An open loop with envelope curve outside virgin curve has been observed in isothermal MR at 300 K for Fe 0.5 Rh 0.5 film on quartz due to supercooling/superheating effect. [ABSTRACT FROM AUTHOR]