Measurements of the anisotropy in permalloy

A measurement system is described, which accurately determines the anisotropy field H/sub k/ and the orientation of the easy-axis in a permalloy film or in any material showing magnetization induced resistance anisotropy. An accuracy of 0.1% in H/sub k/ and 0.1 degrees in easy-axis orientation is reached in permalloy when the applied field strength is 2.5 H/sub k/. Deviations from the Stoner-Wohlfarth single domain model can be recognized after the analysis of the measurement. Four electrical contacts have to be positioned on the permalloy in a planar-Hall configuration. Aluminum contacts realized by a standard lithographic process are used, providing a reference for the easy-axis orientation and an accurate relative orientation of the different planar-Hall elements that can be made out of a single film

Permalloy multilayers to reduce the effects of uniaxial anisotropy

The anisotropic magnetoresistance effect of Permalloy (Ni0.82 Fe0.18) is used in a contactless angle detector. The uniaxial magnetic anisotropy in a Permalloy thin film causes a difference between the direction of magnetization and the magnetic field direction. This leads to a systematic error in the angle detector output. The effects of uniaxial magnetic anisotropy can be reduced by using Permalloy multilayers with different orientations of their anisotropy axes. A double layer with mutually perpendicular anisotropy axes is found to be sufficient for application in an angle detector. The Stoner-Wohlfarth single-domain model is used to describe the systematic error of an angle detector using multilayer

Permalloy thin-film magnetic sensors

An introduction to the theory of the anisotropic magnetoresistance effect in ferromagnetic thin films is given, ending in a treatment of the minimalization of the free energy which is the result of the intrinsic and extrinsic anisotropies of the thin-film structure. The anisotropic magnetoresistance effect in long strips is reviewed. Attention is given to problems like the formation of domains and measures like biasing and linearization. The paper concludes with a description of some applications which are being developed by the authors: (1) an analyser for the stray field of recording heads; (2) a sensitive magnetometer; (3) an accurate absolute angle detector; and (4) an absolute (linear) position detector

Optimization of the response of magnetoresistive elements

A way to optimize the output signal of a general thin-film magnetoresistive element with a homogeneous magnetization field as used in applications with a saturating external magnetic field is presented. The element is assumed to be operated by four-point measurement. In order to be able to compare different elements, a figure of merit is defined. The general theory of the anisotropic magnetoresistance (AMR) effect is treated, and a few general rules for optimization are formulated. It is concluded that in order to obtain a maximum signal voltage amplitude, the current density in the elements should be constant, i.e., not affected by the AMR effect. It is shown, that the AMR effect on the current density in the element usually cannot be neglected. Some special configurations of magnetoresistive elements are treated in detail. The problem of four point contacts in an infinitely wide thin film is solved analytically, with the aid of a special transformation. It is found, that there is an optimum thickness of the thin film in an AMR device, which depends on the material and the deposition technique. For pseudo-Hall elements, an optimum length-to-width ratio is found ( approximately equals 1.35)