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Materials 2018, 11(2), 251; https://doi.org/10.3390/ma11020251

Modulation of Magnetic Properties at the Nanometer Scale in Continuously Graded Ferromagnets

1
CIC nanoGUNE, Tolosa Hiribidea 76, E-20018 Donostia-San Sebastian, Spain
2
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 400, 01328 Dresden, Germany
3
Departamento de Física de la Materia Condensada, Universidad del País Vasco, UPV/EHU, E-48080 Bilbao, Spain
4
NIST Center for Neutron Research, NIST, Gaithersburg, MD 20899, USA
5
School of Chemistry and Materials Science, Rochester Institute of Technology, Rochester, NY 14623, USA
*
Author to whom correspondence should be addressed.
Received: 19 December 2017 / Revised: 25 January 2018 / Accepted: 31 January 2018 / Published: 6 February 2018
(This article belongs to the Special Issue Advances in Superconductive and Magnetic Nanomaterials)
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Abstract

Ferromagnetic alloy materials with designed composition depth profiles provide an efficient route for the control of magnetism at the nanometer length scale. In this regard, cobalt-chromium and cobalt-ruthenium alloys constitute powerful model systems. They exhibit easy-to-tune magnetic properties such as saturation magnetization MS and Curie temperature TC while preserving their crystalline structure over a wide composition range. In order to demonstrate this materials design potential, we have grown a series of graded Co1−xCrx and Co1−wRuw (10 1 ¯ 0) epitaxial thin films, with x and w following predefined concentration profiles. Structural analysis measurements verify the epitaxial nature and crystallographic quality of our entire sample sets, which were designed to exhibit in-plane c-axis orientation and thus a magnetic in-plane easy axis to achieve suppression of magnetostatic domain generation. Temperature and field-dependent magnetic depth profiles have been measured by means of polarized neutron reflectometry. In both investigated structures, TC and MS are found to vary as a function of depth in accordance with the predefined compositional depth profiles. Our Co1−wRuw sample structures, which exhibit very steep material gradients, allow us to determine the localization limit for compositionally graded materials, which we find to be of the order of 1 nm. The Co1−xCrx systems show the expected U-shaped TC and MS depth profiles, for which these specific samples were designed. The corresponding temperature dependent magnetization profile is then utilized to control the coupling along the film depth, which even allows for a sharp onset of decoupling of top and bottom sample parts at elevated temperatures. View Full-Text
Keywords: graded materials; magnetic films; magnetic multilayers; designed magnetic properties; magnetization reversal graded materials; magnetic films; magnetic multilayers; designed magnetic properties; magnetization reversal
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Fallarino, L.; Riego, P.; Kirby, B.J.; Miller, C.W.; Berger, A. Modulation of Magnetic Properties at the Nanometer Scale in Continuously Graded Ferromagnets. Materials 2018, 11, 251.

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