Correlation between Mn oxidation state and magnetic behavior in Mn/ZnO multilayers prepared by sputtering

Compositional, microstructural, and magnetic characterization of [ZnO(30 A)/Mn(x)](n) multilayers prepared by sputtering is presented to study the observed ferromagnetism in the Mn-ZnO system. The nominal Mn layer thickness, x, is varied from 3 to 60 angstrom, while the: number of bilayers, n, is increased to maintain the total amount of Mn constant. Microstructure information was deduced from x-ray reflectivity, Mn oxidation state was determined by x-ray absorption spectroscopy, and magnetic properties were measured over a temperature range of 5-400 K. Magnetic behavior of these samples is found to be related to the Mn layer thickness (x). Multilayers with x >= 30 angstrom exhibit ferromagnetism with a Curie temperature above 400 K, while mostly paramagnetic behavior is obtained for x < 15 angstrom. Magnetic behavior is discussed in terms of electronic and structural parameters of samples. Mn-ZnO interface effect is related to the ferromagnetic order of the samples, but it is not a sufficient condition. The essential role of the Mn oxidation state in the magnetic behavior of this system is pointed out. It is shown a correlation between the obtained ferromagnetism and a Mn oxidation state close to 2+. (c) 2007 American Institute of Physics.