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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Intrinsic magnetic, structural and resistivity properties of ferromagnetic Mn{sub 0.5}Zn{sub 0.5}Al{sub x}Fe{sub 2−x}O{sub 4} nanoparticles

Highlights: ► Al{sup 3+} ion substituted Mn–Zn ferrite nanoparticles. ► Single phase cubic spinel structure changes with Al{sup 3+} substitution. ► Magnetization and coercivity decreased with increasing Al{sup 3+}. ► Resistivity increased with Al{sup 3+} substitution. - Abstract: In this work the nano-structural, magnetic and resistivity properties of Al{sup 3+} substituted Mn–Zn ferrites powders were investigated. Mn{sub 0.5}Zn{sub 0.5}Al{sub x}Fe{sub 2−x}O{sub 4} powders, where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 were obtained by the sol–gel auto-combustion method. X-ray diffraction data indicate that, after substitution, all the samples consisted of the main spinel phase in combination with a small amount of a foreign Al{sub 2}O{sub 3} phase. The addition of Al{sup 3+} resulted in a reduction of particle size and density of the prepared samples. Cation distribution in the present study was estimated by using X-ray diffraction data. The tetrahedral site radii initially increased with Al{sup 3+} content while the octahedral site radii decreased with the Al{sup 3+} substitution. FTIR spectra show two strong absorption bands at 529–548 cm{sup −1} and 445–452 cm{sup −1} which are the typical bands for the cubic spinel crystal structure. The magnetic properties were measured by employing a vibrating sample magnetometer. It was observed that the saturation magnetization, coercivity and anisotropy field decreased with the increase of Al{sup 3+} substitution. Introduction of Al{sup 3+} ions into the Mn–Zn ferrite increased the values of the resistivity, especially in the lower temperature range.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Unoccupied electronic structure of Ni 2 MnGa ferromagnetic shape memory alloy

Momentum resolved inverse photoemission spectroscopy measurements show that the dispersion of the unoccupied bands of Ni 2 MnGa is significant in the austenite phase. Furthermore, in the martensite phase, it is markedly reduced, which is possibly related to the structural transition to an incommensurate modulated state in the martensite phase. Finally, based on the first principle calculations of the electronic structure of Ni–Mn–Ga, we show that the modification of the spectral shape with surface composition is related to change in the hybridization between the Mn 3d and Ni 3d-like states that dominate the unoccupied conduction band.

36 MATERIALS SCIENCE↗