Soft Magnetic And High Frequency Properties Of Ni₇₅Fe₂₅-ZnO Nanogranular Films

With the need for rapid improvement and miniaturization in electromagneticdevices, the nanogranular metal-semiconductor film is increasingly in demand, whichcombines high permeability of magnetic metals with the high resistivity ofsemiconductor.In this work, a series of nanogranular soft magnetic Ni₇₅Fe₂₅-ZnO films wasfabricated and their structures were characterized, and the electrical and magneticproperties and the high-frequency characteristics of complex permeability werestudied.The TEM bright field shows the metal particles are embedded uniformly insemiconductor ZnO matrix. The electronic diffraction pattern further confirms that thesamples are fcc structures, which agreed with the XRD. The average granular size asdetermined by TEM is about4.7nm. The distance between the granular was so close,which was below1nm, that the granular size by XRD was larger than by TEM.When x decreases from0.72to0.52, H_cdoes not exceed5Oe. For Ni₇₅Fe₂₅, theexchange length Lexcan be calculated out to be about153nm, which is much largerthan the metal particle size and the distance between them. Therefore, exchangeinteraction between particles may take place in the wide x range. As a result, thecoercive force is diminished effectively. For the sample of x=0.64, the low coercivityof H_ce=3.62Oe，H_ch=0.506Oe and high resistivity of1790.15μΩcm suggest itspromising for the application in the high frequency range.When the sputtering Ar pressure is0.12Pa, the sample has the soft magneticproperties. So we prepared samples with different thickness t at0.12Pa. Thecoercivity is large when the film thickness is less than100nm, while the coercivitydiminishes rapidly when the film thickness is larger than100nm.For the typical sample with x=0.64, with the frequency below1GHz, μ’ is about120and has slight frequency dependence. With the frequency above1.1GHz, both μ’and μ’’ increase drastically, which is attributed to ferromagnetic resonance （FMR）.