Gagan Sharma

Study of ultrathin magnetic cobalt films on MgO(001)

In-situ magneto-optical Kerr effect measurements have been done to study the evolution of the magnetic properties of ultrathin cobalt films on MgO(001)surface. A magnetic dead layer is found to exist at the MgO/Co interface, thickness of which is influenced by possible surface contamination of MgO substrate. X-ray photoelectron spectroscopy measurements show that etching the substrate with 500 eV Ar ions results in partial removal of carbon contamination. A lower carbon contamination results in reduction of the thickness of dead layer from 2.2 nm to 1.3 nm. At thicknesses below 3 nm, Co islands exhibit superparamagnetic relaxation. For higher film thickness, a well-defined uniaxial magnetic anisotropy develops along (100) direction.

Annealing induced structural changes in amorphous Co23Fe60B17 film on Mo buffer layer

Structural changes occurring in a thin amorphous Co23Fe60B17 film sandwiched between two Mo layers, as a function of thermal annealing has been studied. Thermal stability of the Co23Fe60B17 film is found to be significantly lower than the bulk ribbons. SIMS measurements show that during crystallization, boron which is expelled out of the crystallites, has a tendency to move towards the surface. No significant diffusion of boron in Mo buffer layer is observed. This result is in contrast with some earlier studies where it was proposed that the role of buffer layer of refractory metal is to absorb boron which is expelled out of the bcc FeCo phase during crystallization.

Study of Interfacial Modification in Fe/Ag Multilayer with thermal annealing using X ray Standing Wave

Interfacial modifications in an Ag/Fe/Ag trilayer as function of thermal annealing have been studied using x‐ray standing wave technique. Standing waves are generated using underlying [W/B4C]10 multilayer. In pristine sample Fe on Ag interface is more diffuse as compare to Ag on Fe interface. This result can be understood in terms of difference in surface free energies of Fe and Ag. With thermal annealing the two interfaces exhibit a very different behavior. The observed temperature dependence of interface roughness can be understood in terms of positive heat of mixing and strain energy at the interface. The two interfaces namely Fe on Ag and Ag on Fe exhibit very different behavior as function of annealing temperature.

Enhancement of L10 transformation in Fe/Pt multilayer by Cu addition

Enhancement in L10 transformation kinetics in FePt is achieved by incorporating an optimum concentration of ternary element Cu, which has limited solubility in the fcc FePt phase, into the FePt multilayer stack. Two different multilayer structures were deposited. In first multilayer Cu is deposited at one interface of Fe/Pt and in other Cu is alloyed with Fe and Pt layers by co-sputtering. One Fe42.5Pt42.5Cu15 alloy film is also prepared and detailed study of evolution of structural and magnetic properties as a function of isochronal annealing is done using XRD and Magneto Optic Kerr Effect (MOKE) measurements respectively. Annealing up to 200oC results only in intermixing in the multilayer structure, with no sign of L10 transformation. Annealing at 300oC for 1h results in partial transformation to L10 phase as evidenced by appearance of (001) superlattice peak as well as large increase in the coercivity. It is found that in the Fe(Cu)/Pt(Cu) multilayer exhibits significantly faster L10 transformation as compared to Fe/Pt/Cu multilayer or FePtCu alloy film. Inter-diffusion study using x-ray reflectivity measurements reveals that constant for interdiffusion in Fe(Cu)/Pt(Cu) is only marginally higher than that in Fe/Pt/Cu multilayer. The observed enhancement in L10 transformation rate in Fe(Cu)/Pt(Cu) multilayer is discussed in terms of possible enhancement of diffusivities of constituent species in fcc FePt phase.Enhancement in L10 transformation kinetics in FePt is achieved by incorporating an optimum concentration of ternary element Cu, which has limited solubility in the fcc FePt phase, into the FePt multilayer stack. Two different multilayer structures were deposited. In first multilayer Cu is deposited at one interface of Fe/Pt and in other Cu is alloyed with Fe and Pt layers by co-sputtering. One Fe42.5Pt42.5Cu15 alloy film is also prepared and detailed study of evolution of structural and magnetic properties as a function of isochronal annealing is done using XRD and Magneto Optic Kerr Effect (MOKE) measurements respectively. Annealing up to 200oC results only in intermixing in the multilayer structure, with no sign of L10 transformation. Annealing at 300oC for 1h results in partial transformation to L10 phase as evidenced by appearance of (001) superlattice peak as well as large increase in the coercivity. It is found that in the Fe(Cu)/Pt(Cu) multilayer exhibits significantly faster L10 transformation as ...

Study Of Co90Fe10 Magnetic thin Film On MgO Substrate Using In-situ Moke Technique

Growth behavior of Co90Fe10 film on MgO substrate has been studied. In-situ magneto-optical Kerr effect measurements have been used to study evolution of the magnetic properties of the film with increasing film thickness. Extrapolating linear variation of Kerr signal with film thickness provides the evidence of a magnetic dead layer of thickness 2.2 nm at the interface with MgO substrate. X- ray reflectivity fitting confirms presence of an intermixed layer of about 2 nm.