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We have employed element and chemically sensitive x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) in order to address a long standing controversy regarding the electronic and magnetic states of CuCr2Se4 via halogen doping of the Se anion site in CuCr2Se4-xYx (Y=Cl and Br). Long range magnetic order is observed above room temperature for all samples. The Cr L2,3 XAS spectra show a prevalent 3+ valence for the Cr ions independent of doping concentration and doping agent. The Cu L2,3 XAS spectra show a combination of 1+ and 2+ valence states for all samples. XMCD spectra indicate the presence of a magnetic moment associated with the Cu ions that is aligned antiparallel to the Cr moment. [ABSTRACT FROM AUTHOR]

We investigate the magnetic properties of the isostructural spinel-spinel interface of NiMn2O4(NMO)–Fe3O4. Although the magnetic transition temperature of the NMO film is preserved, both bulk and interface sensitive measurements demonstrate that the interface exhibits strong interfacial magnetic coupling up to room temperature. While NMO thin films have a ferrimagnetic transition temperature of 60 K, both NiFe2O4 and MnFe2O4 are ferrimagnetic at room temperature. Our experimental results suggest that these magnetic properties arise from a thin interdiffused region of (Fe,Mn,Ni)3O4 at the interface, leading to Mn and Ni magnetic properties similar to those of MnFe2O4 and NiFe2O4. [ABSTRACT FROM AUTHOR]

We have employed element and chemically sensitive x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) in order to address a long standing controversy regarding the electronic and magnetic states of CuCr2Se4 via halogen doping of the Se anion site in CuCr2Se4-xYx (Y=Cl and Br). Long range magnetic order is observed above room temperature for all samples. The Cr L2,3 XAS spectra show a prevalent 3+ valence for the Cr ions independent of doping concentration and doping agent. The Cu L2,3 XAS spectra show a combination of 1+ and 2+ valence states for all samples. XMCD spectra indicate the presence of a magnetic moment associated with the Cu ions that is aligned antiparallel to the Cr moment. [ABSTRACT FROM AUTHOR]

Holes can be readily doped into small-gap semiconductors such as Si or GaAs, but corresponding p-type doping in wide-gap insulators, while maintaining transparency, has proven difficult. Here, by utilizing design principles distilled from theory with systematic measurements in the prototype A2 BO4 spinel Co2ZnO4, we formulate and test practical design rules for effective hole doping. Using these, we demonstrate a 20-fold increase in the hole density in Co2ZnO4 due to extrinsic (Mg) doping and, ultimately, a factor of 104 increase for the inverse spinel Co2NiO4, the x = 1 end point of Ni-doped Co2Zn11-xNixO4. [ABSTRACT FROM AUTHOR]