Tomoteru Fukumura

Epitaxial thin films of an oxide-diluted magnetic semiconductor, Mn-doped ZnO, were fabricated by pulsed-laser deposition technique. Solubility of Mn into ZnO exceeds thermal equilibrium limit as a result of nonequilibrium film growth process. As Mn content is increased, the lattice constants of both a and c axes of wurtzite Zn1−xMnxO films (x<0.35) increase and the band gap expands although considerable in-gap absorption develops. Itinerant electrons over 1019 cm−3 can be doped into the

We report on the magnetic properties of an oxide-diluted magnetic semiconductor (DMS), Zn0.64Mn0.36O. The temperature dependence of the magnetization shows a spin-glass behavior with the large magnitude of the Curie–Weiss temperature, corresponding to a stronger antiferromagnetic exchange coupling than other II–VI DMSs. The small effective Mn moment (x̄∼0.02) under high field also represents a strong antiferromagnetic exchange coupling in this compound.

The electric field effect in ferromagnetic semiconductors enables switching of the magnetization, which is a key technology for spintronic applications. We demonstrated electric field-induced ferromagnetism at room temperature in a magnetic oxide semiconductor, (Ti,Co)O(2), by means of electric double-layer gating with high-density electron accumulation (>10(14) per square centimeter). By applying a gate voltage of a few volts, a low-carrier paramagnetic state was transformed into a high-carrier

Magnetic oxide semiconductors, oxide semiconductors doped with transition metal elements, are one of the candidates for a high Curie temperature ferromagnetic semiconductor that is important to realize semiconductor spintronics at room temperature. We review in this paper recent progress of researches on various magnetic oxide semiconductors. The magnetization, magneto-optical effect, and magneto-transport such as anomalous Hall effect are examined from viewpoint of feasibility to evaluate the f

We propose a method of rapid construction of a structural–magnetic–electronic phase diagram of doped Mott insulators. The composition-spread method is utilized for fabricating a film whose doping concentration varies from 0 to 1 continuously. The concurrent x-ray diffractometer that measures x-ray diffraction spectra of all the composition simultaneously, the scanning superconducting quantum interference device microscope, and the infrared optical spectroscopy are employed for characterizing the

Magnetic domain structure on the surface of the layer-structured ferromagnet La1.4Sr1.6Mn2O7 was observed in the temperature range from 37 to 97 kelvin with a scanning Hall probe microscope. The sensitivity to temperature of the domain structure changes was large relative to that in conventional ferromagnets. The stable and spontaneous appearance of magnetic bubble domains without an external magnetic field was observed in the neighborhood of 70 kelvin. The phenomenon observed could provide a po

A scaling relation of the anomalous Hall effect recently found in a ferromagnetic semiconductor (Ti,Co)O2 is compared with those of various ferromagnetic semiconductors and metals. Many of these compounds with relatively low conductivity σxx≤104 Ω-1·cm-1 are also found to exhibit similar relation: anomalous Hall conductivity σAH approximately scales as σAH∝σxx1.6, that is coincident with a recent theory. This relation is valid over five decades of σxx irrespective of metallic or hopping conducti

Magneto-optical spectroscopy of a transparent ferromagnetic semiconductor, anatase TiO2 doped with Co, is carried out at room temperature. A large magneto-optical response with ferromagnetic field dependence is observed throughout from ultraviolet to visible range and increases with increasing Co content or carrier concentration. The magnitude of magnetic circular dichroism (MCD) per unit thickness has a peak around the absorption edge such a huge value of ∼10400 deg/cm at 3.57 eV for a 10 mol%

Electric and magnetic properties of a high temperature ferromagnetic oxide semiconductor, cobalt-doped rutile TiO2, are summarized. The cobalt-doped rutile TiO2 epitaxial thin films with different electron densities and cobalt contents were grown on r-sapphire substrates with laser molecular beam epitaxy. Results of magnetization, magnetic circular dichroism, and anomalous Hall effect measurements were examined for samples with systematically varied electron densities and cobalt contents. The sa