Carrier-induced ferromagnetism in n-type ZnMnAlO and ZnCoAlO thin films at room temperature

Abstract

The realization of semiconductors that are ferromagnetic above room\ntemperature will potentially lead to a new generation of spintronic devices\nwith revolutionary electrical and optical properties. Transition temperatures\nin doped ZnO are high but, particularly for Mn doping, the reported moments\nhave been small. We show that by careful control of both oxygen deficiency and\naluminium doping the ferromagnetic moments measured at room temperature in\nn-type ZnMnO and ZnCoO are close to the ideal values of 5mB and 3mB\nrespectively. Furthermore a clear correlation between the magnetisation per\ntransition metal ion and the ratio of the number of carriers to the number of\ntransition metal donors was established as is expected for carrier induced\nferromagnetism for both the Mn and Co doped films. The dependence of the\nmagnetisation on carrier density is similar to that predicted for the\ntransition temperature for a dilute magnetic semiconductor in which the\nexchange between the transition metal ions is through the free carriers.\n