Effect of induced anisotropy on magnetoimpedance characteristics in NiFe∕Au∕NiFe sandwich thin films

Abstract

The high frequency magnetoimpedance (MI) has been measured in NiFe∕Au∕NiFe narrow sandwich thin films with transverse, longitudinal, and crossed magnetic anisotropies over a frequency range of 50–500MHz. The MI elements have an opened structure with lengths of 2 or 5 mm, widths of 50–200μm and a total film thickness of 1.5μm. The magnetoimpedance characteristics with different field curve shapes, including asymmetrical, have been realized for certain magnetic anisotropy using a dc bias current. Initially the different MI field characteristics have been demonstrated in ferromagnetic microwires with circumferential, helical, and longitudinal anisotropies. Here we have reintroduced these field characteristics for the MI sandwich thin film elements. In an attempt to induce a particular anisotropy in the films the magnetic layers were rf sputtered in the presence of a strong magnetic field, with a further thermal restress treatment of the final MI elements. The use of thin film technology for MI is preferable in many applications because of its compatibility with integrated circuit technology which enables miniaturization, avoiding alignment issues, and wire soldering.