In the past several years, we have reported that electric susceptibility χ' is subject to change with external magnetic field H in ferromagnetic nano-composite oxide sputtered films with a Bi2O3-Fe2O3-PbTiO3 ternary system. The charge displacement current assisted by H and the electric polarization induced by applying a small ac magnetic field, ΔPh(ω), were measured to confirm whether the susceptibility change with magnetic field, Δχ'(H), is intrinsic. In the present study, we found that the detected ΔPh(ω) signal changes depending on both the direction of the magnetic field and the dc bias voltage applied perpendicular to the film plane. To explain these experimental results, we made some alterations to the previous model based on magnetization rotation. From capacitance vs. voltage measurement, it was found that, since we used Si-wafers as substrates, a depletion layer attributed to the MIS structure is formed in the film-to-Si interface. This effect could ultimately be eliminated by applying a forward-biased electric field.
We have studied the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of single spin-valve (SV) films with two different free layers : one is a single ferromagnet layer (conventional), and the other is a ferromagnetic layer with a ruthenium cap layer (Ru cap). When the spacer Cu layer thickness is 2.5 nm and the Ru layer is 0.45 nm, the Ru cap-type greatly enhances the CPP-GMR, with increasing its value up to 4.3%. We argue that the MR enhancement is probably caused by the spin-dependent scattering due to the strong reflection of majority spins at the Co90Fe10/Ru interface.
Thin films of Fe and Fe-N have been prepared using an rf magnetron sputtering system equiped with multipolar magnetic plasma confinement (MMPC), which is efficient for preparation of ferromagnetic thin films at low pressures. For sputtering with 150 W rf-power, the deposition rate of Fe film is 12-14 nm/min, which is three times larger than that of conventional planar magnetron sputtering system. Iron nitride films have been sputter-deposited in an Ar-N2 gas mixture at several pressures, Psp, of 5-0.6 mTorr and the gas flow ratio, fN2 = N2/(Ar + N2), of 0-0.6. The crystalline and morphological structures, the nitrogen content in the film, and the resistivity depend strongly on Psp and fN2. These dependences are explained by the energy of sputtered particles reached at the film surface. In particular, the films prepared at 0.6 mTorr, which is realized by MMPC method, exhibit the crystalline structures of Fe, Fe4N and Fe3N phases depending on fN2, and show the very high purity.
In order to obtain magnetic thin film cores for MMIC (Monolithic Micro-wave Integrated Circuit) inductor, slit patterned CoFe thin films with high saturation magnetization more than 23 kG was fabricated on glass substrate. Annealing effects on the magnetic properties of the film were investigated. The anisotropy field Hk more than 200 Oe was induced together with soft magnetic properties corresponding to GHz-frequency driving. For the much higher driving frequency range of GHz, the Hk is found to be controllable, according mainly to demagnetizing field estimated from geometries of the slit patterned film with the higher saturation magnetization.
This paper describes the use of an Fe-based nanocrystalline alloy ribbon annealed at 550°C for 10 min as a noise filter. An Fe-based nanocrystalline alloy ribbon wound around an input section of a cable exhibited higher noise attenuation than a conventional magnetic ribbon (Co-based amorphous alloy). Further improvement in noise attenuation was achieved by covering the whole cable with the Fe-based nanocrystalline alloy ribbon. This confirmed that an Fe-based nanocrystalline alloy ribbon is a superior candidate for use as a noise filter and cable shielding material.