論文

The micromagnetic structure of the 180° domain wall in submicron-size ferromagnetic Co wires was investigated by means of magnetic force microscopy. The wall width δ (∼μm) observed in Co wire is much larger than that observed in Co films of the same thickness. From micromagnetic calculation using the Landau-Lifshitz-Gilbert (LLG) equation, the magnetic structure of the 180° wall is expected to be a large vortex accompanied by a magnetic ripple structure. This complicated 180° wall is formed to suppress the demagnetizing energy due to a head-on-head configuration of the magnetization, which results in a micron-scale-wide transition area of the wall. The wire-width dependence of the 180° wall width obtained by micromagnetic calculation is almost consistent with that measured from the magnetic force micrograph.

The magnetization process of a hybrid system composed of a soft magnet (Fe-Si) and a superconductor (Bi2Sr2Ca2Cu3Ox) is investigated from the viewpoint of the magnetostatic coupling interaction. The residual magnetization of the hybrid system is higher than that of the superconductor, while the susceptibility is lower than that of the Fe-Si alloy. The behavior is interpreted as due to the occurrence of magnetic image in the superconductor and also to the magnetic flux pinning at the corner of the superconductor.

A new type of highly sensitive magnetometer called a resonating sample magnetometer (RSM) is described. A magnetic sample is mounted on the end of a cantilever rod that incorporates a flat spring with a pick-up coil. The sample is magnetized in a de field, -5 kOe<Ha< +5 kOe,and is simultaneously subjected to a small ac field gradient.The ac field gradient exerts an alternating magnetic force on the sample, proportional to the sample's magnetic moment. The resulting oscillation of the rod is greatly amplified by using the mechanical resonance of the flat Elinvar spring, whose elastic modulus is almost constant in response to temperature variation. The deflection is measured by the pick-up coil. The RSM is considered as a possible system for measuring the temperature variation of magnetization. At room temperature, the sensitivity of the RSM is 6 × 10-7 emu, and a complete hysteresis loop can be measured in about 15 min.