Soft magnetic properties of NiFeTa thin films for biasing film applications in magnetoresistive elements

Abstract

The effects of Ta addition on the magnetic properties of permalloy thin films have been investigated. The alloy compositions on a weight basis are (Ni₈₁Fe₁₉)_1-x Ta _x with 0 ⩽ x ⩽ 0.105, and the films are sputtered onto a glass substrate at between room temperature and 300 ‡C. The saturation magnetization and anisotropic magnetic field decrease with increasing Ta content. The saturation magnetization is 0.75 T at 5 wt % Ta. The coercivity remains constant at 125 Am^-1. The electrical resistivity increases linearly with increasing Ta content, then saturates at approximately 7.5 wt% Ta. The saturation resistivity is approximately 1.00 ΜΩm. The magnetoresistivity ratio (δϱ/ϱ) decreases with increasing Ta content, mainly due to increased electrical resistivity (ϱ). The magnetostriction changes from negative to positive with increasing Ta content and reaches nearly zero at 2 wt% Ta. The NiFeTa films containing 5–6 wt% Ta have potential for use as the soft-biasing film in magnetoresistive elements.