Europium oxynitride ferromagnetic semiconductors

At room pressure and temperature the system EuOsub(1-x)Nsub(x) has two solid-solubility ranges, each with the NaCl structure: for 0 =< x =< 0.30 the system is ferromagnetic and semiconducting above the Curie temperature; for 0.92 =< x <1 it is metallic. Conductivity and Seebeck voltages indicate intrinsic behaviour above 310 K with an energy gap that decreases with increasing x for 0 =< x =< 0.30. Magnetic susceptibilities are consistent with 4f6 configurations at x europium ions per molecule and a ferromagnetic Curie temperature Tsub(C) that increases with x. Low-temperature transport measurements were made only for 0.20 =< x =< 0.30: a minimum in the electrical conductivity, approximately 30 K above Tsub(C) correlates well with the onset of an anomalous low-temperature crystal contraction and with deviations from a Curie-Weiss law typical of short-range magnetic order. Below Tsub(C) there is a metal-to-semiconductor transition similar to that found in EuOsub(1-delta). The magnitude of the negative Seebeck coefficient increases with T between Tsub(C) and 310 K as might be expected for an extrinsic conductor with a transport contribution similar to the kinetic contribution, as in a metal. (author)