Showing papers by "P. K. Mukhopadhyay published in 2006"

Powder x-ray diffraction study of the thermoelastic martensitic transition in Ni 2 Mn 1.05 Ga 0.95

Abstract: Results of temperature-dependent magnetic susceptibility and powder x-ray diffraction (XRD) measurements on ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{105}{\mathrm{Ga}}_{095}$ and ${\mathrm{Ni}}_{213}{\mathrm{Mn}}_{087}\mathrm{Ga}$ magnetic shape memory alloys are compared The transformation behavior of these two alloys is found to be entirely different Detailed LeBail and Rietveld analyses of powder XRD data of ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{105}{\mathrm{Ga}}_{095}$ alloy show that the martensite phase belongs to the Pnnm space group with $7M$ modulation The limits of the supercooled austenite and the superheated martensite phases have been determined by Rietveld analysis of powder XRD data recorded at close temperature intervals It is shown that the martensite and the austenite phases coexist over $\ensuremath{\sim}30\phantom{\rule{03em}{0ex}}\mathrm{K}$ temperature range around the martensitic transition temperature The transformation strains during cooling in [001], [010], and [100] directions are found to be $\ensuremath{-}4%$, $+16%$, and $21%$, respectively, while the volume change is only 006%

Phase diagram and electronic structure of Ni 2+x Mn 1-x Ga

Abstract: We determine the phase diagram of Ni2+xMn1�xGa as a function of x 0x 0.35 from ac susceptibility and differential scanning calorimetry DSC. Total energy and density of states calculated using the ab initio full potential linearized plane-wave FPLAPW method explain the phase diagram. A martensitic paramagnetic phase for x 0.2 has been identified. The structure of this phase is found to be tetragonal from hightemperature x-ray-diffraction XRD studies. XRD, magnetization, and DSC measurements show that the paramagnetic tetragonal phase evolves from the lower temperature ferromagnetic tetragonal phase through a second-order phase transition without any change of structure. The unoccupied conduction band has been studied by inverse photoemission spectroscopy. It is dominated by Mn 3d-like states, and is in good agreement with FPLAPW based calculations.

Magnetic and hyperfine properties of nanocrystalline Ni0.2Zn0.6Cu0.2Fe2O4 prepared by a chemical route

Abstract: Nanoparticles of Ni0.2Zn0.6Cu0.2Fe2O4 were prepared by the standard co- precipitation method. The formation of nanocrystalline mixed spinel phase has been confirmed by x-ray diffractograms. The sizes of the nanoparticles were estimated in the range 7-30 nm, which was confirmed by transmission electron microscopy. Thermal variations of the real part of AC magnetic susceptibilities measured from 450 K down to 80 K and Mossbauer effect measurements at room temperature and down to 20 K clearly indicate the presence of superparamagnetic particle si n allthe samples. Specific saturation magnetizations measured by VSM are found to increase steadily with the increase of average particle size. The coercive field obtained from low frequency measurements shows that in all the samples a small fraction of particles is not relaxed within the measuring time. For samples showing a less dominating superparamagnetic behaviour, AC magnetic susceptibility data showed the expected increase of blocking temperature with increase in particle size. Magnetic anisotropy energy constants of the nanoparticles were estimated from the blocking temperature and the values cannot be directly correlated with their particle sizes.

Experimental and theoretical study of annealed Ni-Pt alloys

Abstract: In this communication we present a detailed study of the magnetic properties of ordered Ni-Pt alloys. We study the alloys through field-cooled and zero-field cooled dc magnetization, nonlinear ac s ...