抄録
To reduce the spike noise caused by stray magnetic fields, we investigated layered stacking soft-magnetic underlayers (SULs) with interlayer magnetic coupling. To reduce SUL noise as well, nanocrystalline or amorphous materials are used in the large part of the soft-magnetic layer. Through investigation of material problems in ferromagnetic (FM)/nonmagnetic (NM) stacked SULs and antiferromagnetic (AFM)/ferromagnetic (FM) stacked SULs, the following points were clarified: (1) In the case of FM/NM stacked layers using Ru as the NM layer and CoZrNb as the FM layer, when the layer structure of CoZrNb (150 nm)/Ru (0.6 nm)/CoZrNb (150 nm) was adopted, the M-H loop was shifted due to RKKY interlayer exchange coupling. The value of the interlayer exchange coupling constant J was derived at a small value of 0.015 erg/cm2. (2) In the above layer structure, by sputtering the Ru layer under At + O2 atmosphere, or by introducing a Co70Fe30 layer which has high saturation magnetization Ms, between the Ru layer and CoZrNb layer, the value of Hex and J were enhanced. The J value shows prospects of enhancement over one digit if appropriate materials and process are introduced. (3) In AFM/FM stacked SULs, the unidirectional anisotropy constant Jk between the AFM and FM layers was reduced by increasing the thickness of the FM layer. The principal problem is how to suppress the reduction of Jk by controlling the soft magnetic properties of the FM layer.
