Eur. Phys. J. B (2013) 86: 136
https://doi.org/10.1140/epjb/e2013-30933-6

Regular Article

Tailoring the magnetic anisotropy of thin film permalloy microstrips by combined shape and induced anisotropies^*

¹ Departamento de Electricidad y Electrónica, Universidad del País Vasco, UPV/EHU, P.O. Box 644, 48080 Bilbao, Spain
² BCMaterials, Universidad del País Vasco, UPV/EHU, P.O. Box 644, 48080 Bilbao, Spain
³ Departamento de Química Física, Universidad del País Vasco, UPV/EHU, P.O. Box 644, 48080 Bilbao, Spain

^a e-mail: alf@we.lc.ehu.es

Received: 12 October 2012
Received in final form: 21 January 2013
Published online: 8 April 2013

Abstract

The sensitivity of magnetic sensors based on the Giant Magneto-Impedance effect can be enhanced using high permeability materials with a well-defined but small transverse anisotropy. We describe an experimental study performed on multilayered, permalloy-based thin films deposited by sputtering under a magnetic field that produces a homogeneous uniaxial anisotropy in the plane of the film. Patterning of the deposit by photolithographic methods into strip-shaped samples (with their long direction perpendicular to the induced anisotropy) establishes a longitudinal shape anisotropy that competes with the transversal one induced at deposition. The combination and competition of the two mutually perpendicular uniaxial anisotropies result in an effective one with a reduced magnitude (the difference between both of them) in the transversal direction. As the strength of the shape anisotropy is determined by the relation between width and length of the stripe, the magnitude of the effective anisotropy can be conveniently modulated by adequately selecting the aspect ratio of the patterned sample. The hysteresis loops measured by Kerr effect magnetometry confirm that the effective transversal anisotropy field can be reduced from 5 to 1 Oe which should concomitantly increase the sensitivity of thin film magneto-impedance sensors.