Neutron-Diffraction Investigation of CuCr2Se4and Cu

Abstract

Neutron-diffraction measurements at 508°K as well as x-ray-diffraction measurements at room temperature show the compounds CuCr 2 Te 4 and CuCr2Se4 to have a normal spinel structure. The coherent scattering length of Se was found to be 0.779X 10~1 2 cm. The neutron-diffraction diagrams below the transition temperature confirm the ferromagnetic behavior proposed by Lotgering. The magnetic moment of the Cu ion in the tetrahedral site is zero, whereas the magnetic moments of the Cr ions in the octahedral site are approximately three Bohr magnetons, corresponding with Cr 3+ . * B. 0. Loopstra, Nucl. Instr. Methods 44, 181 (1966).

Magnetism and transport of CuCr2Se4 thin films

“…They exhibit a wide range of electronic and magnetic behavior. [2][3][4][5][6] Within the family of chalcogenide spinels, the basic structural parameters, such as the S-S or Se-Se distances, as well as thermal properties such as thermal expansion are very similar for most members of the family, so epitaxial growth of thin isostructural layers is generally possible. Therefore, one can imagine synthesizing and fabricating an all-chalcogenide spinel multilayer magnetic device.…”

Electronic structure of halogen doped CuCr2Se4

“…The main difference between the two models resides in the valence states and associated magnetic contributions of the Cr and Cu ions. To date there have been a similar number of experimental papers based on magnetization and Hall effect measurements supporting both theories (3,4,7,8).…”

“…Two theoretical models have been proposed over the years. The first one by Lotgering (5) suggests an electronic configuration of Cu + (Cr 3+ Cr 4+ )Se [2][3][4] where the ferromagnetism is due to the indirect coupling of the Cr 3+ ions spins with the Cr 4+ ones through 90° Se bonds, while the Cu + ions do not contribute since they have a full 3d shell. The metallicity of the system is explained in terms of hole conduction in the few empty valence band levels formed by Se 2-p and Cr 4+ d states.…”

“…The compound has been extensively studied in bulk form in the 60's-70's and characterized as a metallic ferromagnet with Curie temperature (T C ) of approximately 440 K (3,4). However, the details of the electronic and magnetic state of CuCr 2 Se 4 remain controversial.…”

“…The metallicity of the system is explained in terms of hole conduction in the few empty valence band levels formed by Se 2-p and Cr 4+ d states. The second model by Goodenough (6) suggests a configuration of Cu 2+ (Cr 3+ ) 2 Se [2][3][4] where the overall ferromagnetism (or more correctly the ferrimagnetism) is mainly due to the contributions of two opposing magnetic moments -one associated with the super-exchange interaction of Cr 3+ ions through 90° Se bonds and the other with a Cu 2+ delocalized hole. In this model the metallic behavior is associated with the t 2g orbitals of the delocalized Cu 2+…”