Low-temperature magnetization of (Ga,Mn) As semiconductors

Journals published by the American Physical Society can be found at http://journals.aps.org/We report on a comprehensive study of the ferromagnetic moment per Mn atom in (Ga,Mn)As ferromagnetic semiconductors. Theoretical discussion is based on microscopic calculations and on an effective model of Mn local moments antiferromagnetically coupled to valence band hole spins. The validity of the effective model over the range of doping studied is assessed by comparing with microscopic tight-binding/coherent-potential approximation calculations. Using the virtual crystal k center dot p model for hole states, we evaluate the zero-temperature mean-field contributions to the magnetization from the hole kinetic and exchange energies, and magnetization suppression due to quantum fluctuations of Mn moment orientations around their mean-field ground state values. Experimental low-temperature ferromagnetic moments per Mn are obtained by superconducting quantum interference device and x-ray magnetic circular dichroism measurements in a series of (Ga,Mn)As semiconductors with nominal Mn doping ranging from similar to 2 to 8%. Hall measurements in as-grown and annealed samples are used to estimate the number of uncompensated substitutional Mn moments. Based on our comparison between experiment and theory we conclude that all these Mn moments in high quality (Ga,Mn)As materials have nearly parallel ground state alignment

Resonant soft X-ray scattering - a new probe of charge, spin and orbital ordering in the manganites

SoftX-rayresonant diffraction is a new technique pioneered by our group. We have published examples of the huge resonant enhancements of charge and magnetic scattering that can be obtained at the L-edges of 3d transition metaloxides. In this paper we will also show how resonant soft X-ray scattering enables direct observation of orbital ordering. We have studied the low temperature phase of La0:5Sr1:5MnO4 that displays charge, spin and orbital ordering. We have employed resonant soft X-ray scattering at the manganese L edges which provide a direct measurement of the orbital ordering. Energy scans at constant wave vector have been compared to theoretical predictions and show that at all temperature s there are two separate contributions to the observed scattering, direct Goodenough orbital ordering and strong cooperative Jahn–Teller distortions of the Mn3þ ions. Finally, we will show how that the spin and orbital degrees of freedom are strongly correlated in these materials.JRC.E.6-Actinides researc