We studied the optical and magnetic properties in epitaxial AlN/GdN/AlN double heterostructures grown using reactive sputtering under ultrapure conditions. The indirect and direct optical transitions in a 95-nm-thick GdN film were found to be 0.95 and 1.18 eV, respectively. The considerable size effects of the optical band gap were observed with a decrease in the GdN thickness. The AlN/GdN/AlN double heterostructures clearly exhibited ferromagnetic states at low temperature. The short-range correlation of spins began to develop below ∼60 K, and long-range ordering that obeyed the Arrott relation was confirmed below ∼30 K. Because of the film-size independence for the ferromagnetic ordering, the cooperative correlation length in GdN was considered to be shorter than 30 nm. Furthermore, we found that the band gap is dramatically reduced with the ferromagnetic spin ordering.

An exceptional kind of spin splitting in the band structure of AlN/GdN/AlN double heterostructures has been studied by employing temperature-dependent spectroscopy. This spin splitting can be attributed to both the band-gap shrink and the difference between minority and majority band energies in GdN below the Curie point; these results have been established by evaluating the optical band gaps at the X-point. The temperature-dependent magnetization measurements that provide direct evidence of the magnetic ordering below 32 K and it is described by long-range spin correlation in GdN.

Quantitative analysis of the angle dependence of planar Hall effect observed in ferromagnetic GaMnAs film J. Appl. Phys. 105, 07C501 (2009); 10.1063/1.3055354 Co-doped TiO 2 films grown on glass: Room-temperature ferromagnetism accompanied with anomalous Hall effect and magneto-optical effect Appl. Phys. Lett. 94, 102515 (2009); 10.1063/1.3095664 Microstructure, magnetic, and optical properties of sputtered Mn-doped ZnO films with high-temperature ferromagnetism

We studied the ferromagnetic phase transition and the resultant change in the optical band gap of GdN thin films grown by a reactive sputtering technique in an ultra‐high vacuum process. The GdN thin film exhibited two phases of spin ordering; the short correlation of spins starts to develop below ∼60 K, and the long‐range ferromagnetic ordering emerges below the Curie temperature of 37 K. GdN has been confirmed to be an indirect band gap semiconductor. We found that the band‐gap is dramatically reduced with the ferromagnetic spin ordering. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigated the narrowband ultraviolet emission properties of Al 0.94 Gd 0.06 N phosphor thin films pumped by an electron beam. An extremely narrow luminescence line, which was less than 1 nm from the intra-orbital f-f transition in Gd 3þ ions, was confirmed at 318 nm. The corresponding emission efficiency was improved by decreasing the growth temperature. The extended X-ray absorption fine structure analysis of the local atomic structure revealed that a low-temperature growth led to the formation of a uniform atomic configuration around Gd, which was found to play a key role in improving the luminescence intensity of the films. V