Reading thin film permanent magnet irregular patterns using magnetoresistive sensors

TL;DR

This paper explores reading irregular, non-periodic magnetic patterns on thin films using magnetoresistive sensors, proposing a theoretical model and analyzing spatial resolution limits for potential industrial magnetic encoders.

Contribution

It introduces a novel approach to reading non-uniform magnetic patterns with magnetoresistive sensors and provides a theoretical model matching experimental data.

Findings

Magnetic scans of CoCrPt structures with varied separations were successfully obtained.

A theoretical model accurately describes the magnetic field of irregular patterns.

Spatial resolution decreases beyond a certain reading distance depending on feature size.

Abstract

Magnetic encoders currently provide accurate positioning information by reading periodic patterns with equally spaced structures or bits. As this technology evolves to fulfill industrial demands for cheaper and more accurate systems, variations of this concept with non-periodic and non-predetermined patterns emerge. In this work, we take the first step towards the development of such devices using equally sized bits with different separations. We show magnetic scans of 1000 {\mu}m wide and 2000 {\AA} thick CoCrPt structures with separations between 63 and 3000 {\mu}m, obtained with tunnel magnetoresisistive sensors. A theoretical model to describe the magnetic field created by these structures is also proposed, which matches the trend of the experimental signals. We also show that there is a spatial resolution loss for reading distances higher than a threshold that depends on the minimum feature size of the sample.