arXiv subjects

H. Toyosaki

Publications and source records attributed to H. Toyosaki.

8 recordsLinked to original sources

arXiv2011

Bulk and Surface Magnetization of Co atoms in Rutile Ti_[1-x]Co_xO_[2-delta] Thin Films Revealed by X-Ray Magnetic Circular Dichroism

We have studied magnetism in Ti_[1-x]Co_xO_[2-δ] thin films with various x and δby soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L_[2,3] absorption edges. The estimated ferromagnetic moment by XMCD was 0.15-0.24 μβ/Co in the surface, while in the bulk it was 0.82-2.25 μβ/Co, which is in the same range as the saturation magnetization of 1.0-1.5 μβ/Co. Theseresults suggest that the intrinsic origin of the erromagnetism. The smaller moment of Co atom at surface is an indication of a magnetically dead layer of a few nm thick at the surface of the thin films.

cond-mat.mtrl-sci↗

arXiv2006

Indication of intrinsic room-temperature ferromagnetism in Ti1-xCoxO2-d thin film: An x-ray magnetic circular dichroism study

Soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L2,3 edges of Co doped rutile TiO2 at room temperature have revealed clear multiplet features characteristic of ferromagnetic Co2+ ions coordinated by O2- ions, being in sharp contrast to the featureless XMCD spectrum of Co metal or metallic clusters. The absorption and XMCD spectra agree well with a full atomic-multiplet calculation for the Co2+ high-spin state in the D2h-symmetry crystal field at the Ti site in rutile TiO2. The results indicate that the ferromagnetism arises from the Co2+ ions substituting the Ti4+ ions.

cond-mat.mtrl-sci↗

arXiv2006

Signature of Carrier-Induced Ferromagnetism in Ti_{1-x}Co_{x}O_{2-delta}: Exchange Interaction Between High-Spin Co 2+ and the Ti 3d Conduction Band

X-ray photoemission spectroscopy measurements were performed on thin-film samples of rutile Ti_{1-x}Co_{x}O_{2-delta} to reveal the electronic structure. The Co 2p core level spectra indicate that the Co ions take the high-spin Co 2+ configuration, consistent with substitution on the Ti site. The high spin state and the shift due to the exchange splitting of the conduction band suggest strong hybridization between carriers in the Ti 3d t2g band and the t2g states of the high-spin Co 2+. These observations support the argument that room temperature ferromagnetism in Ti_{1-x}Co_{x}O_{2-delta} is intrinsic.

cond-mat.str-el↗

arXiv2005

A ferromagnetic oxide semiconductor as spin injection electrode in magnetic tunnel junction

A magnetic tunnel junctions composed of room temperature ferromagnetic semiconductor rutile Ti1-xCoxO2-d and ferromagnetic metal Fe0.1Co0.9 separated by AlOx barrier showed positive tunneling magnetoresistance (TMR) with a ratio of ~11 % at 15 K, indicating that Ti1-xCoxO2-d can be used as a spin injection electrode. The TMR decreased with increasing temperature and vanished above 180 K. TMR action at high temperature is likely prohibited by the inelastic tunneling conduction due to the low quality of the amorphous barrier layer and/or the junction interface.

cond-mat.mtrl-sci↗

arXiv2005

Evolution of ferromagnetic circular dichroism coincident with magnetization and anomalous Hall effect in Co-doped rutile TiO2

Magnetic circular dichroism (MCD) of rutile Ti1-xCoxO2-d is systematically examined with various x and d to reveal a phase diagram for the appearance of ferromagnetism at higher carrier concentration and Co content. The phase diagram exactly matches with that determined from anomalous Hall effect (AHE). The magnetic field dependence of MCD also shows good coincidence with those of the magnetization and AHE. The coincidence of these independent measurements strongly suggests single and intrinsic ferromagnetic origin.

cond-mat.mtrl-sci↗

arXiv2005

Magnetic oxide semiconductors

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 ferromagnetism. The ferromagnetism of Co-doped TiO2 and transition metal-doped ZnO is discussed.

cond-mat.mtrl-sci↗

arXiv2003

Carrier induced ferromagnetism in room temperature ferromagnetic semiconductor rutile TiO2 doped with Co

A ferromagnetic semiconductor, rutile (Ti,Co)O2, exhibits anomalous Hall effect at room temperature. Strong dependence of the anomalous Hall effect, as well as the magneto-optic response, on the carrier concentration suggests carrier induced ferromagnetism in this compound. Both ferromagnetic responses are caused by the charge carriers at the band edge of host semiconductor, indicating possibilities of spintronics devices operable at room temperature.

cond-mat.mtrl-sci↗

arXiv2003

Exploration of oxide-based diluted magnetic semiconductors toward transparent spintronics

A review is given for the recent progress of research in the field of oxide-based diluted magnetic semiconductor (DMS), which was triggered by combinatorial discovery of transparent ferromagnet. The possible advantages of oxide semiconductor as a host of DMS are described in comparison with conventional compound semiconductors. Limits and problems for identifying novel ferromagnetic DMS are described in view of recent reports in this field. Several characterization techniques are proposed in order to eliminate unidentified ferromagnetism of oxide-based DMS (UFO). Perspectives and possible devices are also given.

cond-mat.mtrl-sci↗