Two different silica sources have been used for the preparation of Ni0.5Zn0.5Fe2O4/SiO2 nanocomposites,and their effects on the particle size,crystallinity and the magnetic properties have been investigated by Xray diffraction(XRD),transmission electron microscopy(TEM) and physical property measurement system(PPMS).In both cases,Ni0.5Zn0.5Fe2O4 nanoparticles of 11 nm in mean particle size were well dispersed in silica matrix.The coercivity and the blocking temperature of Ni0.5Zn0.5Fe2O4 nanoparticles modified with the silicon coupling agent show little decrease,whereas the saturation magnetization increases obviously with respect to nanoparticles dispersed directly in silica matrix.It is considered that the decrease of the surface anisotropy resulting from the change in the surface coordination is responsible for the observed behavior.
Wei ZhangHongxia WangFaling ZhangZhengnan QianWenhui Su
The magnetocaloric effect of LaFe11.7Si1.3 compound was investigated under an external magnetic field up to 9 T.The magnetization changed drastically at the Curie temperature TC under different fields and TC increased with the applied fields.The magnetic entropy change |?SM| vs temperature peak consisted of a spike and a plateau.The spike was a spurious result,while the plateau part resulted from the field-induced itinerant-electron metamagnetic(IEM) transition above TC,which went up with magnetic fields increasing.The width of the magnetic entropy change increased with magnetic fields at a rate of dL?S /dT^4 K/T.
