Europhys. Lett.
Volume 68, Number 1, October 2004
Page(s) 100 - 105
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 September 2004
Europhys. Lett., 68 (1), pp. 100-105 (2004)
DOI: 10.1209/epl/i2004-10178-5

Structural and magnetic properties of oxide films $\chem{CoFeHfO}$: A possible candidate for all-oxide TMR junctions?

M. Eßeling, Y. Luo and K. Samwer

I. Physikalisches Institut, Universität Göttingen Tammannstr. 1, D-37077 Göttingen, Germany

received 13 February 2004; accepted in final form 9 August 2004

In search of a magnetic oxide, which is insensitive to oxygen at interfaces and thus appropriate as an electrode layer for tunneling junction applications, we prepared thin films of $\chem{CoFeHfO}$ by reactive DC-magnetron sputtering technique and investigated the relation between structural and magnetic properties. The results suggest that the films consist of two disorded phases, a $\chem{Co(Fe)}$-rich and a $\chem{HfO}$-rich. It was found that the degree of film homogeneity and thus the magnetic nature depends on preparation conditions such as film thickness and deposition rate. A second magnetic phase with a high saturation field, which is present in thicker films, could therefore be reduced by decreasing the film thickness. Consequently, the thinnest film (10 $\un{nm}$) is nearly single phased and exhibits an excellent uniaxial anisotropy with a coercive field $H_{\ab{c}}$ of 16 $\un{Oe}$ along the easy axis. Additionally, thermomagnetic measurements were carried out to understand annealing-induced effects. A clear improvement with increased saturation magnetisation ( $M_{\ab{s}}=695$ $\un{emu/cm^{3}}$) and decreased $H_{\ab{c}}$ was observed, which can be attributed to structural relaxation and phase separation caused by annealing.

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

© EDP Sciences 2004