International audienceNiFe2O4(111) ultrathin films (3-5 nm) have been grown by oxygen-assisted molecular beam epitaxy and integrated as effective spin-filter barriers. Structural and magnetic characterizations have been performed in order to investigate the presence of defects that could limit the spin filtering efficiency. These analyses have revealed the full strain relaxation of the layers with a cationic order in agreement with the inverse spinel structure but also the presence of antiphase boundaries. A spin-polarization up to þ25% has been directly measured by the Meservey-Tedrow technique in Pt(111)/NiFe2O4(111)/c-Al2O3(111)/Al tunnel junctions. The unexpected positive sign and relatively small value of the spin-polarization are discussed, in comparison with predictions and previous indirect tunnelling magnetoresistance measurement
First-principles calculations have been used to investigate the effects of Co addition on the preferred site occupation and magnetic properties of Ni-Fe-Ga-Co ferromagnetic shape memory alloys. The formation energy results indicate that the excess Ni constituent preferentially occupies the Fe sites in the off-stoichiometric Ni-Fe-Ga ternary alloy. The added Co tends to take the normal-Ni sites in the Ni-Fe-Ga-Co quaternary alloy during composition adjustment process. The total magnetic moment increases with Co content of the Ni36-xFe12Ga16Cox (x=0, 1, 2, 3 and 4) alloys. The difference between the up and down electronic density of states at the Fermi level gives rise to the increased magnetic property.
In this paper, the martensitic transformation temperature, the microstructure and the crystal structure of the complicated martensitic phases of Ni56-xFe19Ga25Cox (x =0, 1.5, 3, 4.5, 6) alloys were investigated by DSC, XRD, SEM and TEM techniques. DSC results show that the martensitic transformation temperature Tm, which is above the room temperature, decreases with the increasing Co content. The microstructure of the Ni56-xFe19Ga25Cox (x =0, 1.5, 3, 4.5, 6) alloys is composed by the martensitic lath and randomly distributed γ phase. The 6M+14M mixed modulated martensite and the γ second phase were detected in the Ni53Fe19Ga25Co3 alloy by XRD and TEM tests.
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