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The European Physical Journal B, 2013, 86:136.
Alfredo Garcia-Arribas, Eduardo Fernández, Andrey V. Svalov, Galina V. Kurlyandskaya, Ane Barrainkua, David Navas, José Manuel Barandiaran.1883. Departamento de Electricidad y Electrónica, Universidad del Pais Vasco, UPV/EHU, P.O. Box 644, 48080, Bilbao, Spain and
2883. BCMaterials, Universidad del Pais Vasco, UPV/EHU, P.O. Box 644, 48080, Bilbao, Spain and
3883. Departamento de Quimica Fisica, Universidad del Pais Vasco, UPV/EHU, P.O. Box 644, 48080, Bilbao, Spain.
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.
Additional Information
The Giant Magnetoimpedance Effect (GMI) in thin film-based magnetic microstructures is a promising alternative for low field magnetic field sensing, in direct competition with AMR (Anisotropic Magnetoresistance) and even fluxgate sensors.The GMI effect consists in the huge change of the electrical impedance experienced by a soft magnetic material under the influence of an external (low magnitude) magnetic field. The sensitivity of GMI sensors can be enhanced using high permeability materials with a well-defined but small transverse anisotropy. The paper describes 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 (aspect ratio) 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. Further work performed after the publication of the paper confirms that the combined effect of both anisotropies allows improving the sensitivity of the GMI effect upon increasing the aspect ratio of the samples. The hysteresis loops presented in the accompanying figure correspond to a new set of sandwiched magnetic structures, composed by two stacks ofPermalloy/Titanium multilayers (as the ones studied in the paper) together with a non-magnetic layer situated between them. The anisotropy field presents the same decrease tendency with the increase of the aspect ratio, but the GMI effect is boosted by the beneficial effect of the sandwiched structure. The sensitivity for a sample 2 mm long and 50 mm wide reach a value of 3.7 W/Oe, measured at 300 MHz.
Thin film structures for sensing applications is a active research line of the new scientific center BCMaterials (http:\\www.bcmaterials.net).
