Snehal Jani

Phase evolution in F57e/Al multilayers studied through dc magnetization, conversion electron Mössbauer spectroscopy, and transmission electron microscopy

Fe/Al multilayer thin films with an overall atomic concentration ratio of Fe:Al=1:2 have been prepared by ion-beam sputtering. Phase formation and microstructural evolution with thermal annealing have been studied by x-ray reflectivity, cross-sectional transmission electron microscopy, dc magnetization, and conversion electron Mossbauer spectroscopy. These studies show that although the starting composition is Al rich, the intermixing of Fe and Al at the interfaces leads to the formation of a magnetic Fe3Al-like region at the interface. Thus, the magnetic contribution in the as-deposited multilayer structure (MLS) is not only from pure Fe but also from an Fe3Al-like region formed at the interface. On annealing the MLS, a stable nonmagnetic MLS consisting of intermetallic B2 Fe50Al50 separated by thin Al layers is formed. Further annealing only induces better ordering of Fe50Al50 and does not destroy the MLS.

Magnetic and transport properties in thin film of Fe2CrAl

Preliminary results on magnetic and transport properties of a thin film of disordered Fe2CrAl deposited on (111) Si by pulsed laser deposition is reported in this study. While the bulk arc melted ingot used as target for the deposition is purely ferromagnetic, the film shows the co-existence of different magnetic phases, which arises due to the granular nature of the film. This is because, although the average composition pertains to Fe2CrAl, local disorder results in the formation of grains with different magnetic states that may be ferromagnetic or may consist of magnetic clusters. The resulting magnetic inhomogeneity of the thin film leads to large values of negative temperature coefficient of resistance of ∼22%/K at 260 K.

Thickness Dependent Structure and Magnetic Properties in 57Fe/Ti/Co Multilayers

Structural and magnetic properties of 57Fe/Ti/Co multilayers (MLs), prepared by Ion beam sputtering on Si substrate have been studied as a function of trilayers (TLs) thickness and modulation periods. X-ray reflectivity (XRR) shows the successful growth of high-quality layered structures along with up to 3rd order Bragg peaks with distinct Kiessig oscillation. X-ray diffraction (XRD) and Mössbauer studies evidence the formation of different phases mainly at the interfaces. Soft magnetic properties with high saturation values (~800emu/cm3) and high anisotropy field (~20kOe) are observed in the room temperature magnetization curve. The in plane value of coercivities are 18Oe and 60Oe for the 12 and 24 TLs respectively while in the out-of plane direction it increases to nearly 8 and 12 times respectively. The 12 TLs sample shows the presence of two fold anisotropy whereas the 24 TLs sample shows an isotropic behaviour. Low temperature DC magnetization studies evidence the presence of weak antiferromagnetic coupling while the Kelly Henkel plots for these samples show that the dominant exchange interactions between the grains are ferromagnetic.

Uniaxial anisotropy induced in 57Fe/Co/Al multilayers

The magnetic properties of 57Fe/Co/Al multilayers with 20 and 40 trilayers, deposited on Si (100) substrate using ion beam sputtering, are reported here. X-ray reflectivity and X-ray diffraction studies indicate the formation of good quality films with preferential growth along the (110) direction. Conversion electron Mossbauer spectra show considerable inter-mixing between the layers and the formation of Fe-Al/Fe-Co-Al phases. The samples are extremely soft with coercivities ≤0.48 × 103 A/m, exhibit strong in-plane uniaxial anisotropy and calculations show that they possess a high ferromagnetic resonance frequency of ∼2 GHz. The saturation magnetization value of 1.80 × 106 A/m is comparable with that obtained in multilayer samples with much higher content of Co. The combination of magnetic properties in these multilayers thus makes them ideal candidates for high frequency device applications.

Magnetic properties of Al/57Fe/Cr multilayers

Conversion Electron Mossbauer Spectroscopy (CEMS) and DC magnetization are used to compare magnetic properties of as-deposited multilayer (MLS) and Fe2CrAl thin film made from Al/57Fe/Cr MLS deposited by ion beam sputtering and then annealed in UHV. Interdiffusion of elements on annealing sample-1 at 500°C leads to formation of a single, disordered film of Fe2CrAl as evidenced by hyperfine field values obtained by CEMS in the film which compares well with that in bulk Fe2CrAl. CEMS also shows contributions from Fe, Fe/Cr and Fe/Al interfaces in the MLS. Saturation magnetization of as-deposited sample-1 is much less than pure Fe due to reduced Fe thickness because of interface formation and also reduction in Fe-Fe interaction due to intervening Al and Cr layers.

MOKE Study of Fe/Co/Al Multilayers

The multilayer system (MLS)‐[57Fe25 A/Co11 A/Al17 A]×20 has been deposited by Ion beam sputtering (IBS) technique. The MLS has been annealed at 700 °C for 1 h. Overall composition of as deposited and annealed MLS have been characterized by EDX and magnetic properties have been studied through angular dependent magneto optic Kerr effect (MOKE) hysteresis curves. The study shows that the as‐deposited MLS has excellent soft magnetic properties coupled with perpendicular magnetic isotropy which is destroyed on annealing.

Magnetic Properties of Disordered Fe3Al

The magnetic properties of Fe3Al powders prepared by filing the ingot in both as‐filed and annealed form are studied. Results of Mossbauer, X‐ray diffraction and DC magnetization studies show that the magnetic properties are modified due to formation of non‐magnetic Fe3AlC0.5 phase due to C intercalated on filing. The hyperfine fields obtained are explained in terms of nearest and next nearest neighbor configurations of 57Fe.