Magnetoresistance in amorphous oxide films

Y. Luo; M. Eßeling; K. Zhang; G. Güntherodt; K. Samwer

doi:10.1209/epl/i2005-10402-x

All issues

Volume 73 / No 3 (February 2006)

Europhys. Lett., 73 3 (2006) 415-421

Abstract

Issue		Europhys. Lett. Volume 73, Number 3, February 2006


Page(s)		415 - 421
Section		Condensed matter: electronic structure, electrical, magnetic, and optical properties
DOI		https://doi.org/10.1209/epl/i2005-10402-x
Published online		21 December 2005

Europhys. Lett., 73 (3), pp. 415-421 (2006)

Magnetoresistance in amorphous oxide films $\chem{CoFeHfO}$

Y. Luo¹, M. Eßeling¹, K. Zhang², G. Güntherodt³ and K. Samwer¹

¹ I. Physikalisches Institut, Universität Göttingen - Friedrich-Hund-Platz 1 D-37077 Göttingen, Germany
² II. Physikalisches Institut, Universität Göttingen - Friedrich-Hund-Platz 1 D-37077 Göttingen, Germany
³ II. Physikalisches Institut, RWTH Aachen - Templergraben 55 D-52056 Aachen, Germany

Corresponding author: yluo@gwdg.de

Received: 15 July 2005
Accepted: 1 December 2005

Abstract

This paper shows results on structural and magnetotransport measurements for reactively sputtered amorphous oxide films ( ${\rm Co}_{55}{\rm Fe}_{20}{\rm Hf}_{25})_{1-{x}}{\rm O}_{x}$ with $x \leq 0.35$ and their layered structures. A strong x-dependency was found to be related to microstructural changes caused by oxygen-induced chemical phase separation. For low x, $\chem{Co\tx{-}Co(Fe)}$ pair-correlated atom clusters dominate and the films are soft ferromagnetic with excellent uniaxial magnetic anisotropy. Small coercivity $H_{c} \approx 1\tx{--}4$ Oe, enhanced magnetisation $M_{s} \approx 420$ emu/cm³ and low resistivity $\rho \approx 10^{-4}$ Ωcm were measured for these films, showing a good potential for application in magnetoelectronics. For large x, however, since $\chem{Hf}$ - $\chem{O}$ pair-correlated atom clusters are dominant, the films become granular-like superparamagnetic with a saturation field $H_{s} > 20$ kOe and a remanence $M_{r}/M_{s} \approx 0$ . ρ is extremely high presumably due to Coulomb blockade effect. A large magnetoresistance was observed, being 30% (70 kOe) at 5 K and 10% at room temperature. This effect can be attributed to spin-dependent tunnelling among lateral separated $\chem{Co}$ - $\chem{Co(Fe)}$ clusters. The layered structure shows a small, but low-field magnetotunnelling effect.

PACS: 75.70.-i – Magnetic properties of thin films, surfaces, and interfaces / 75.50.-y – Studies of specific magnetic materials

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