High resolution imaging of ac magnetic field from a trailing-edge shielded perpendicular magnetic writing head was demonstrated by using frequency-modulated magnetic force microscopy (FM-MFM) with a high-coercivity FePt MFM tip. The distribution of perpendicular magnetic field gradient of the recording head is presented and can be used to evaluate the recording performance of the head. A Fourier analysis of the images suggests that magnetic spectral features as small as 15 nm should be detectable by using the FM-MFM technique with a high coercivity tip. The enhancement in spatial resolution of FM-MFM is very crucial for the analysis of nanoscale magnetic features and to shed light on the development of next generation magnetic recording heads.

A new magnetic force microscopy (MFM) technique for measuring alternating magnetic field (ac magnetic field) was proposed by using frequency modulation (FM) phenomenon of tip oscillation. We detected a narrowband FM phenomenon in the tip oscillation of a high-coercivity MFM tip by applying an ac magnetic field to the tip by using a metal-in-gap (MIG) type ring head. In the experiment, the MFM tip was driven at a constant frequency fc near the resonant frequency of the cantilever by a piezoelectric element, and the ac magnetic field with a frequency fm up to 10 kHz was applied to the MFM tip. Two sideband spectra with a frequency of fc±fm were observed by applying ac magnetic field. The intensity of sideband spectra increased linearly with increasing applied current value of the MIG head. It was observed that FM occurred from the analysis of frequency spectra of the MFM signals. This FM phenomenon is caused by the force applied on the cantilever by the field gradient of the head. The FM phenomenon is understood by solving the differential equation for the harmonic oscillator of which the effective spring constant is changed periodically by ac magnetic field. The FM phenomenon can be used for imaging ac magnetic fields.

A new Heusler alloy, Fe2(Mn,Cr)Si, that is likely to have high spin polarization (P) and high damping constant (α) was proposed to obtain high magneto-resistance ratio and low spin torque noise in a magnetic read head with a current-perpendicular-to-plane (CPP) giant magneto-resistance (GMR) multilayer. A very high frequency (VHF) plasma irradiation process during radio frequency (RF) sputter deposition was investigated to form the highly ordered structure of the Heusler alloy film with low thermal treatment temperature. The main results are as follows: (1) P and magnetic moment of Fe2(Mn0.5Cr0.5)Si with an L21 structure were estimated at 0.99 and 2.49 µB/f.u., respectively, and α was also estimated to be larger compared with the case of Co2MnSi, according to density of states (DOS) calculations. (2) The ordering (at least B2 structure) temperature of Fe2(Mn0.6Cr0.4)Si film decreased from 500 to 300 °C by using the VHF plasma irradiation process with optimized condition. (3) The surface roughness of Fe2(Mn0.6Cr0.4)Si film also reduced from 1.7 to 0.5 nm by using the VHF plasma irradiation process. It is found that the Fe2(Mn,Cr)Si Heusler alloy and the VHF plasma irradiation process with optimized condition seems to be applicable for fabrication of high-performance magnetic read head with CPP-GMR device.

Direction detectable static magnetic field imaging, which directly distinguishes the up and down direction of static perpendicular magnetic field from a sample surface and the polarity of magnetic charges on the surface, was demonstrated for CoCrPt-SiO2 perpendicular magnetic recording media based on a frequency-modulated magnetic force microscopy (FM-MFM), which uses a frequency modulation of the cantilever oscillation induced by an alternating force from the tip-sample magnetic interaction. In this study, to generate the alternating force, we used a NiFe soft magnetic tip driven by the ac magnetic field of a soft ferrite core and imaged the direction and the amplitude of the static magnetic field from the recorded bits. This method enables measurement of the static magnetic field near a sample surface, which is masked by short range forces of the surface. The present method will be effective in analyzing the microscopic magnetic domain structure of hard magnetic samples.

(Bi1-xBax)FeO3 multiferroic thin films with ferromagnetism and ferroelectricity were fabricated and applied to create magnetic recordings using an electric field. The (001)-oriented (Bi1-xBax)FeO3 thin films of which electric polarization direction is perpendicular to the film plane were fabricated onto a non-single-crystalline substrate with a Ta seedlayer / (111)-oriented Pt underlayer at a low substrate temperature of 500 ℃. A very high frequency plasma irradiation was applied during sputtering deposition of (Bi1-xBax)FeO3 to accelerate the crystallization at the low substrate temperature. The fabricated (Bi0.6Ba0.4)FeO3 film exhibited hysteresis curves indicating ferromagnetic and ferroelectric behavior. The saturation magnetization of the film was approximately 60 emu/cm 3 and the coercivity was approximately 2.5 kOe, respectively. Magnetic Force Microscopy analysis of the (Bi0.6Ba0.4)FeO3 film confirmed that the magnetization was reversed by applying only a local electric field. The multiferroic film described here is expected to be useful for electric field-driven magnetic devices.