Preparation And Magnetic Properties Of Nano CoFeB And Ni Soft Magnetic Materials

Magnetic materials with low dimensional (such as thin films and nanowires arrays) have been widely studied, for their potential applications in modern high-frequency magnetic devices with smaller size and lower energy consuming. In most cases, magnetic materials with out-of-plane anisotropy are essential. It is focused on the way to control the magnetic anisotropy of low-dimensional magnetic materials. For their high resistant, high saturation magnetization, and low coercivity, Co-based amorphous materials have received much attention. But their properties are sensitive to large and sudden change in temperature, because they are in the sub-stability state commonly. This confined their range of applications. In this thesis, amorphous CoFeB thin films, nanotube arrays, and nanowire arrays are obtained by electroless plating, Ni nanowire arrays are obtained by electrode plating. By applying a magnetic field during the plating process, the magnetic anisotropy of nanowire arrays can be tuned. The structure relaxation of amorphous CoFeB thin film and nanotube arrays are studied by thermo-magnetic treatment (annealing under a magnetic field). The phase composition is determined by X-ray diffraction. The morphology is observed by scanning electron microscope, and the elements ratio is analyzed by energy disperse spectroscopy. co-scan mode is used to analyze the textures in Ni nanowire arrays. The magnetic properties are tested by vibrating sample magnetometer. Combined with hysteresis loops, angular dependent He, and first order reversal curves, the effect of applying a magnetic field during the plating process on the reversal mechanism of nanowire arrays is discussed, and the structural relaxation during the thermomagnetic treatment process of amorphous thin films and nanotube arrays is revealed.Thermomagnetic treatment at different angles between the normal direction of film and the annealing magnetic field affect the properties of amorphous CoFeB films. Thermomagnetic treated at certain angle can improve the magnetic properties of the amorphous film. XRD results show that, the short-range directional order of atoms is increased by the annealing thermomagnetic treatment. This structural relaxation process induced decrement of free volume, some particles appeared on the surface of the films.The axial magnetic anisotropy of amorphous CoFeB nanotube arrays can be enhanced by applying a magnetic field parallel to the long axis during electroless plating process. When the applied field increased, the axial magnetic anisotropy of nanotube arrays is enhanced with the atomic short-range ordering increased. The deposited CoFeB nanotubes have very good thermal stability under small magnetic field。The reversal mechanism of CoFeB nanowire arrays is relevant to the nanowire diameter. The results of angular dependent Hc tests showed that, the reversal mechanism of nanowire array is changed from curling mode to the compound mode of curling and transverse with the diameter increased. CoFeB nanowires with different morphologies are obtained with different electroless plating process. The filling ratio is increased with the sensitization and activation treatment times increased. Blown to dry after rinsed in sensitize and activation solutions, under moderate stiring, with suitable reducing agent concentration, and adding moderate PEG into the electroless plating solution can prevent the premature blocking of pores, which is benefit to fabricate nanowire arrays with high quality. The magnetic anisotropy of amorphous CoFeB nanowire (D>200nm) array can be tuned by applying a magnetic field during plating process. The easy magnetization direction of nanowire array turned from parallel to perpendicular to the long axis with the applied magnetic field increased. The results of first order reversal curves showed that, the irreversible part in nanowire arrays increased by the applied magnetic field. The arrangement of magnetic moments in nanowires is changed. The ordering degree of atom-pairs along the axial direction is increased, and a kind of pseudo-magnetocrystalline anisotropy is formed then. The direction of easy magnetization direction is determined by the shape anisotropy, the pseudo-magnetocrystalline anisotropy, and the interwire magnetostatic interaction.The Ni nanowire arrays obtained in AAO templates with20nm diameter have strong (110) texture. The diffusion degree of (110) texture is increased with the length of nanowire is increased. By applying a axial magnetic field during the plating process, the magnetic anisotropy of Ni nanowire arrays along the direction of field is enhanced, the diffusion degree of (110) texture is changed also. Nanowire arrays plated under the magnetic field of600Oe obtained the lowest diffusion degree of (110) texture, the largest grain size, and the strongest axial magnetic anisotropy.