Macroscopic Quantum Tunneling of Magnetic Domain Wall in Ferromagnetic Composite Thin Films

The purpose of this investigation is to clarify the quantum tunneling of magnetic domain wall into the pinning center in the composite thin film consisting of hard ferromagnet，soft ferromagnet and superconductors.This study is composed of three parts；(1)the magnetization reversal process in ferromagnetic composite wire having a pinning center，(2)the magnetization reversal process in composite thin films，and(3)the galvanomagnetic effect in very thin ferromagnetic wire。The results are summarized as follows.(1)The magnetization reversal process and the wall displacement velocity in submicron Fe-Ni wire with tri-layer structure were investigated by measuring the electric resistance。The wall mobility was estimated to be about2.6m/sOe，due to Gilbert damping process。(2)The magnetostatic interaction dominates the magnetization process of hybrid films consisting of ferromagnetic Fe and superconducting Nb。The domain structure in the Fe film may depend on whether Nb is superconducting or not，and this affects the magnetization reversal.(3)The conductance of the nanowire produced by a tip and contact method was quantized in the unit of 2e D 12 I D 1/h below 67 Oe and e I D 12 D 1/h above 67 Oe.The spin degeneracy plays an important role in the conductance quantization.Unfortunately，the existence of the quantum macroscopic tunneling was hard to confirm at least present stage。

The purpose of this investigation is to clarify the quantum tunneling of magnetic domain wall into the pinning center in the composite thin film consisting of hard ferromagnet , soft ferromagnet and superconductors. This study is composed of three parts ; (1) the magnetization reversal process in ferromagnetic composite wire having a pinning center, (2) the magnetization reversal process in composite thin films, and (3) the galvanomagnetic effect in very thin ferromagnetic wire. The results are summarized as follows. (1) The magnetization reversal process and the wall displacement velocity in submicron Fe-Ni wire with tri-layer structure were investigated by measuring the electric resistance. The wall mobility was estimated to be about 2.6 m/sOe, due to Gilbert damping process. (2) The magnetostatic interaction dominates the magnetization process of hybrid films consisting of ferromagnetic Fe and superconducting Nb. The domain structure in the Fe film may depend on whether Nb is superconducting or not, and this affects the magnetization reversal. (3) The conductance of the nanowire produced by a tip and contact method was quantized in the unit of 2eィイD12ィエD1/h below 67 Oe and eィイD12ィエD1/h above 67 Oe. The spin degeneracy plays an important role in the conductance quantization. Unfortunately, the existence of the quantum macroscopic tunneling was hard to confirm at least present stage.