Magnetic properties of MBE-grown Zn1-xCrxTe

We have grown Zn1-xCrxTe films by molecular-beam-epitaxy (MBE) and investigated their magnetic properties with variation of Cr concentrations (x) between 0.01-0.08. Systematic increase of the lattice constant was observed by XRD only up to around x = 0.02. Measurements of the magnetizations M-H reveal that ferromagnetic transition occurs in the films at low temperatures. The transition temperature (T-C) which was estimated from Arrott-plots increased with Cr concentration up to about 100 K for x = 0.08. However, the temperature dependence of the magnetization M-T shows different curves below T-C for field-cooled (FC) and zero-field-cooled (ZFC) processes. Moreover, their paramagnetic Curie temperatures (theta), estimated from the higher temperature M-T curves, are different from and much higher than T-C. These behaviours could be attributed to the superparamagnetism in the films. Indeed, many defects such as stacking faults are observed in the sample with x = 0.08 through HRTEM. It could give rise to the distribution of the Cr concentrations and/or the presence of precipitates including Cr. (C) 2004 WILEYNCH Verlag GinbH & Co. KGaA. Weinheim