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

TL;DR

This study demonstrates room-temperature ferromagnetism in n-type ZnMnO and ZnCoO thin films through precise control of oxygen deficiency and aluminium doping, showing carrier-induced magnetic properties relevant for spintronics.

Contribution

It reveals that careful doping and oxygen control induce near-ideal ferromagnetic moments and establishes a correlation between carrier density and magnetization in ZnO-based ferromagnetic semiconductors.

Findings

Room-temperature ferromagnetism achieved in ZnMnO and ZnCoO films.

Magnetization correlates with carrier-to-donor ratio.

Magnetization dependence matches theoretical predictions for carrier-mediated exchange.

Abstract

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