Soft magnetic properties of nanocrystalline amorphous HITPERM films and multilayers

Amorphous precursors to HITPERM (Fe, Co)-Zr-B-Cu (a-HITPERM) films and a-HITPERM/SiO₂ multilayer films have been deposited on glass or Si substrates by a rf sputtering system with a target of composition (Fe_0.7Co_0.3)₈₈Zr₇B₄ Cu₁. It was found that the a-HITPERM single layer film with a thickness of 100 mm possessed good soft magnetic properties with a saturation magnetization of 4πM_s⩾14 kG and a coercivity of H_c~0.9 Oe at room temperature. Hc increases from 0.9 Oe to 25 Oe when the him thickness increases from 100 to 150 nm. To obtain excellent soft magnetic properties at larger thicknesses, a-HITPERM/SiO₂ multilayer films have been synthesized. In these, H_c drops from 25 Oe (single layer) to 0.25 Oe (multilayers) with the same total a-HITPERM thickness. The intervening SiO₂ layers play an important role in reducing the coercivity. Experimental results show the optimum thickness for SiO₂ was 2-4 nm. M-H loops for the multilayers films exhibit pronounced two step magnetization reversal processes for temperatures between 5 and 25 K. This behavior can be attributed to magneto-static coupling between a-HITPERM layers and sequential switching of the layers. The coupling exhibits itself in a blocked phenomenon with wide (stepped) hysteresis curves for T<25 K and smooth narrow hysteresis curves for T>25 K. The effects of magneto-static coupling on the magnetic properties of a-HITPERM/SiO₂ films will be discussed