Modulating Permalloy Thin Films on Grating Structure for Anisotropy Magnetic Sensor

Abstract

Magnetoresistive effect means that the conductivity of martial will be affected by external field $(\text{H}_{\text{ext}})$ . Anisotropic magneto resistivity (AMR) is a kind of magneto resistivity (MR), AMR has violent variation of MR because of spin-orbital coupling effect. The effect has relation to the angle of magnetization field to current flow. The research fabricates a modulated permalloy (Py, Ni 80 Fe 20 ) magnetic nanostructure using the holographic technique realized in a degenerate two-wave mixing experiment and exhibited a sinusoidal profile with a periodicity of around $1\mu \text{m}$ [1]. Thus, we use photolithography to define grating structure with a periodicity of around $3\mu \text{m}$ . Next, the grating structures are etched to various depths by reactive ion etcher (RIE). Finally, they are deposited modulating Py thin films by ion beam sputtering (Fig. 1). Due to shape anisotropy, the magnetization of thin film will align to the long-axis of groove direction. Therefore, the magnetic properties of the Py thin films are affected by the groove construction. The sample with 20nm Py shows an uniaxial magnetic anisotropy with an easy and hard axis direction. When $\text{H}_{\text{ext}}$ is following with the groove direction $(\text{H}_{\text{ext}}$ at 0° easy axis), the magnetization switches in a clear Barkhausen jump, (Fig. 2(a), black dot). For $\text{H}_{\text{ext}}$ is perpendicular to the groove direction $(\text{H}_{\text{ext}}$ at 90°; hard axis)(Fig. 2(b), red dot), with a more narrow hysteretic cycle than last one. According to the result, the thickness of Py film and the structure of sample both affect M(H) loop. We aim to complete the highly sensitive AMR sensor. grating with $3\mu \text{m}$ (a)20 nm and(b)20 nm with H is parallel and vertical to the groove direction