MAGNETIC PROPERTIES OF NICKEL NANOPARTICLES IN THE NIOBIUM OXIDE MATRIX
Heterogeneous ferromagnetic-insulator materials containing nanosized Ni particles have been obtained by ion-beam sputtering of composite target consisting of a nickel base and plates from Nb <sub>2</sub>O <sub>5</sub>. The nickel concentration in the obtained Ni <sub>x</sub>(Nb <sub>m</sub>O <sub>n</sub>) <sub>100-x</sub> samples varies in the range of 17 - 54 at.%. It was found that the values of the tunneling magnetoresistance (TMR), observed in the Ni <sub>x</sub>(Nb <sub>m</sub>O <sub>n</sub>) <sub>100-x </sub>samples, are several times less than similar TMR values in other nickel based composites with another dielectric matrix. The samples with low Ni content does not exhibit TMR, although their magnetization in a magnetic field is nonzero at room temperature. Cooling of these samples to 77 K leads to appearance of the TMR effect. Presumably these features are associated with high defect of the dielectric matrix, presence of the oxide layer on the surface of metal granules, low values of Curie temperature and large spread in size of the nickel granules