Studies Of Preparations, Structures And Properties Of Nano-composite Magnetic Thin Films

The GMR and GMI effects in magnetic materials have greatly improved the sensitivity and accuracy of magnetic measurements and the density of magnetic recording. Nanocrystalline soft-magnetic materials have been extensively attracted due to their excellent magnetic properties. The methods, principles and techniques of nanocrystalline soft-magnetic thin films prepared by magneto-sputtering were introduced in this paper. The properties of these thin films were measured by X-ray diffraction and 57Fe Mossbauer spectroscopy. The main conclusions are as follows:(1) Fe-Si-B-Nb-Cu thin films were prepared by radio frequency (rf) magneto-sputtering. The influence of sputtering power on the microstructure of thin films has been studied. The results show that thin films, deposited with low sputtering power density, are amorphous, but with the increasing of sputtering power density thin films turn into the mixture structure of crystals and amorphous phase WITHOUT any annealing treatment. Crystals contain nano-sized a-Fe(Si) anda-Fe(B) solid solutions and their volume fractions gradually increase with sputtering power, whereas those of amorphous phase decreases. In a-Fe(B) solid solution, the replacing probability of B atoms also increases with the increasing sputtering power, which results in the decreasing of the hyperfine field of a-Fe(B) solid solution. The corresponding hyperfine field is 235KOe, 229KOe, 223KOe and 218KOe with the sputtering power of 50, 100, 150 and 200W respectively.(2) The orientation of magnetic moment of the thin films is dependence of the sputtering power. The angle between the orientation of magnetic moment and the normal axis of film surface decreases with the increasing sputtering power. With low sputtering power, magnetic moments are mostly parallel to film surface, but the angle is gradually decreasing with the increasing sputtering power.(3) The influence of the orientation of magnetic moment on the macro-magnetism of thin films has been studied through magnetization in different directions. The results show that the ratio of remained magnetization to saturated magnetization (Mr/Ms) decreases with the increasing of the angle between the orientation of magnetic moment and the direction of magnetization, which indicates that magnetic properties of thin films are closely dependence of the anisotropy of grains.(4) FeCuNbSiB thin films are composite embedded structure of nano-crystals Si-rich Si(Fe)and Fe-rich Fe(Si) solid solution, while sputtering power was set on 400W. The appearance of Si-rich solid solution, the pinning effect and the decreasing of the volume fraction of the soft-magnetic a-Fe (Si) solid resolution leads to the variation of the soft-magnetic properties of the thin films.(5) NiFe/Ge multilayers were cross deposited by rf and dc magneto-sputtering alternately. The multilayers were analyzed by X-ray diffraction, Mossbauer spectroscopy and VSM. The results show that sample(a), with the composite structure of NiFe-based and Fe-based nanocrystalline solid solution embedded in amorphous matrix, presents soft-magnetization, while sample(b) consists of Fe, Ni and Ge nanocrystals and NiFeN FeGe, FeGeNi nanocrystals formed the composite structure of several types of nanocrystals embedded in amorphous matrix. Some of grains present paramagnetism. NiFe and FeGeNi nanocrystals present soft-magnetism and appearance of some hard-magnetism phase. The He and Hsat of sample (b) increase due to the exchange coupling between the hard magnetic phase and the soft magnetic phase thus leads to the difference of the mechanisms between demagnetization and magnetization of the thin film.