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Magnetic properties of nanogranular composites CoFeZr -Alumina

Alexander K. Fedotov 1,  Julia A. Fedotova 1,  Yury E. Kalinin 2,  Alexander V. Sitnikov 2

1. Belarusian State University (BSU), F. Skaryna av. 4, Minsk 220050, Belarus
2. Voronezh State Technical University, Voronezh, Russian Federation

Abstract

The 5 to 15 mm thick nanocomposite films of CoFeZrin alumina matrix were sputtered in the chamber evacuated with pure Ar gas. It is shown that magnetic state of the films was strongly dependent on concentration X of CoFeZr nanoparticles. The films being before percolation threshold Xc

= 40-45 at.% displayed superparamagnetic state of metallic nanoparticles with the lack of sextet in Mössbauer specta, non-hysteresis character of magnetization curves and invariability of real m1 and imaginary m2 parts of magnetic permeabilities measured at frequences 20-200 MHz. Beyond the Xc, the values of m1 were increased with X elevation due to decrease of interparticle distances. As a result, the effects of dipole-dipole and exchange interactions of nanoparticles became apparent resulting in the presence of magneto-ordered regions (magnetoclusters) including a few nanoparticles. The formation of net of magnetoclusters was observed using MFM and Mossbauer measurements. The observed changes in magnetic properties of nanocomposites with x fully agree with our earlier DC/AC measurements revealed peculiarities of hopping carrier transport, negative magnetoresistance and impedance at Xc.
 

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Presentation: Oral at E-MRS Fall Meeting 2006, Symposium A, by Alexander K. Fedotov
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-12 15:57
Revised:   2009-06-07 00:44