Paper-based spintronics: magneto-resistivity of permalloy deposited onto paper substrates

TL;DR

This study explores the use of paper substrates for magneto-resistive sensors with permalloy coatings, demonstrating potential for low-cost, flexible magnetic sensing devices through experimental analysis of magneto-resistance behavior.

Contribution

It introduces a novel approach of fabricating magneto-resistive permalloy films on paper substrates and investigates their magnetic and electrical properties.

Findings

Magneto-resistance of permalloy on paper shows classical behavior at ±45° angles.

Formation of magnetic domain walls observed at fiber bending locations.

Paper-based sensors exhibit measurable magneto-resistive effects comparable to traditional substrates.

Abstract

Driven by low-cost, resource abundance and distinct material properties, the use of paper in electronics, optics and fluidics is under investigation. Considering sensor systems based on magneto-resistance principles (anisotropic, giant, tunnel) that are conventionally manufactured onto inorganic semiconductor materials, we propose the use of paper substrates for cost reduction purposes primarily. In particular, we studied the magneto-resistance sensitivity of permalloy (Py:Ni81Fe19) onto paper substrates. In this work, we report on our findings with clean room paper (80 g/m2, Rrms = 2.877 {\mu}m, 23% surface porosity, latex impregnation, no embossed macro-structure). Here, the Py:Ni81Fe19 coating was manufactured by means of a dry process, sputter deposition, and spans an area of 10x10 mm2 and a thickness of 70 nm. Employing a four-point-probe DC resistivity measurement setup, we investigated the change of electrical resistance of Py:Ni81Fe19 under the presence of an oriented external magnetic field. In particular, we investigate the magneto-resistive change at two configurations: (1) the direction of the magnetic field is parallel to the nominal induced electric current and (2) the direction of the magnetic field is perpendicular to the electric current. Due to the stochastic orientation of the fibers interplaying with the Py:Ni81Fe19 coating, the change in magneto-resistance of the overall system at both measurement configurations closely corresponds to the classical response of Py:Ni81Fe19 at a +/-45{\deg} angle between the direction of electrical current and magnetic field. Using the magneto-optic kerr effect, we observed the formation of domain walls at the fiber bending locations. Future work will focus on the impact of layer thickness, fiber dimensions and structure of magnetic coating on the performance of the paper-based Py:Ni81Fe19 magneto-resistors.