Nano-structured Exchange-spring Hard Magnetic Thin Films

AbstractIn exchange coupled nano-composite magnets, the length scale of the soft phase is limited to twice the domain wall thickness of the hard phase. We investigated the structural and magnetic properties of SmCo5/Co exchange coupled multilayer grown by magnetron sputtering from Sm and Co targets successively at elevated substrate temperature and subsequent in-situ annealing. X-ray diffraction indicates the formation of polycrystalline SmCo5 hard phase. Formation of hard/soft multilayered structure was confirmed through transmission electron microscopy. Magnetic hysteresis measurements showed single phase like behavior, which indicates the soft layer (Co) is well exchange coupled with the neighboring hard phase of SmCo5. Maximum energy product of 15.37 MGOe with HC ∼ 3.02 kOe was obtained

Properties and preparation of high quality, free-standing GaN substrates and study of spontaneous separation mechanism

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Understanding thickness dependent magnetic properties of Tb-Fe thin films

In this paper, we have attempted to understand the magnetic behaviour of Tb-Fe thin films grown with different thicknesses through detailed electron microscopy, magnetization measurements and magnetic domain imaging studies. Tb-Fe thin films over a range of thicknesses such as 50, 100, 200, 400, 600 and 800 nm were deposited on Sisubstrates using electron beam evaporation technique. Grazing incidence X-ray diffraction studies revealed that all the films were amorphous in nature. Microstructural studies using transmission electron microscopy showed columnar channel of voids extending from substrate to film surface. Magnetization measurements along the in-plane and out-of-plane direction indicated presence of out-of-plane magnetic anisotropy in all the films. Saturation magnetization and coercivity measured along the out-of-plane direction were found to vary with the thickness of the films. A very high coercivity of ~2000 mT was obtained for the film having thickness of 400 nm. Magnetic anisotropy calculations indicated a strong perpendicular magnetic anisotropy for the 400 nm thick film. The variation of magnetic anisotropy with film thickness was correlated with the magnetic domain patterns observed in the films using magnetic force microscopy

Properties of non-polar a-plane GaN/AlGaN quantum wells

The structural and optical properties of a series of GaN/Al0.18Ga0.82N multiple quantum well (MQW) structures, in which the well thickness was varied between 2 and 8 nm, grown on a-plane (1 1 0) GaN on r-plane (1 0 2) sapphire substrates have been investigated. High-resolution X-ray diffraction and low-angle X-ray reflectivity measurements were used to determine the well and barrier thicknesses and the barrier composition after matrix transformation of the (binary) elastic constants for the appropriate coordinates, and assuming a pseudo-morphically strained system. The microstructure of the (1 1 0) samples is dominated by I1-type basal-plane stacking faults (BSF) terminated by partial dislocations or prismatic stacking faults, as determined by conventional and high-resolution transmission electron microscopy. The low temperature photoluminescence (PL) spectra of the QW structures show two emission bands which are assigned (partly based on photoluminescence excitation (PLE) spectroscopy) to excitons that are confined solely by the quantum wells and, at lower energy, those carriers that recombine in the region where the wells are intersected by BSFs. Both bands shift to higher energy with decreasing quantum well thickness. The optical data indicate that the non-polar (1 1 0) GaN/AlGaN system is free of polarization-induced electric fields, since the QW exciton emission energy is not below the band-edge emission energy of the GaN template