Grant-in-Aid for Scientific Research (A)
|Allocation Type||Single-year Grants |
Applied materials science/Crystal engineering
|Research Institution||Tokyo Institute of Technology |
YAMAUCHI Hisao Tokyo Institute of Technology, Materials and Structures Laboratory, Professor, 応用セラミックス研究所, 教授 (50271581)
HAMADA Noriaki Tokyo University of Science, Faculty of Science and Technology, Professor, 理工学部, 教授 (00126145)
MOTOHASHI Teruki Tokyo Institute of Technology, Materials and Structures Laboratory, Assistant Professor, 応用セラミックス研究所, 助手 (00323840)
KARPPINEN Maarit (KARPPINEN Maar) 東京工業大学, 応用セラミックス研究所, 助教授 (50334529)
|Project Period (FY)
2003 – 2006
Completed (Fiscal Year 2006)
|Budget Amount *help
¥41,210,000 (Direct Cost: ¥31,700,000、Indirect Cost: ¥9,510,000)
Fiscal Year 2006: ¥2,990,000 (Direct Cost: ¥2,300,000、Indirect Cost: ¥690,000)
Fiscal Year 2005: ¥4,030,000 (Direct Cost: ¥3,100,000、Indirect Cost: ¥930,000)
Fiscal Year 2004: ¥12,090,000 (Direct Cost: ¥9,300,000、Indirect Cost: ¥2,790,000)
Fiscal Year 2003: ¥22,100,000 (Direct Cost: ¥17,000,000、Indirect Cost: ¥5,100,000)
|Keywords||Halfmetals / Spintronics / Transition-metal oxides / Double-perovskites / Mixed valence state / Mossbauer spectroscopy / FLAPW band calculations / スピンエレクトロニクス|
Halfmetallic materials are anticipated to play a key role for emerging next-generational electronics called spintronics. Nonetheless only a handful number of such materials have been known to date. In the present research, development of new layered-oxide halfmetallic materials was conducted, consisting of the works on (1) search for new halfmetals, (2) development of high quality halfmetallic bulk materials and (3) quest for room-temperature halfmetals.
High-quality samples of oxygen-deficient layered double-perovskite oxides, BaRECo2O5+8 with RE=Nd, and Sin were synthesized by means of our original techniques which allow us to control the oxygen content with high accuracy, and studied in terms of magneto-transport and other related properties. In particular the sample, BaNdCo_20_<5.503> with δ = 0.503±0.003 exhibited large magneto-resistance of a tunneling-type for a temperature interval of 230 -260 K. Although the lower limit of this temperature
interval shows due to the appearance of anti-ferromagnetism, the magnitude of MR at 230 K (a relatively high temperature) is as high as 12 % at 7 T. Thus this layered- oxide material was found to be halfmetallic at temperatures close to the ice point.
Members of a new oxide family, (LaMn)_<1-x>O_3, were successfully synthesized employing a high-pressure technique. It was found that as had been predicted from a band calculation (by a (LSDA + U) method), (LaMn)_<0.901>O_3 was proven to show colossal magneto-resistance (CMR) below 250 K probably due to a double exchange mechanism. Our recent detailed study by neutron diffraction on the magnetic structure of this material supports the identification of this material as a halfmetal.
(2)Homocomposites consisting of double-perovskite, Sr_2FeMoO_6
A B-site ordered double-perovskite, Sr_2FeMoO_6 (SFMO), is known as a halfmetal (with T_C = 420 K). In order to improve the tunneling magneto-resistance characteristics of bulk halfmetals, an original concept of "homocomposite" was developed as a fashion of halfmetallic polycrystalline bulks. Two or more powders of different sizes of the same material are mixed before sintered into a homocomposite bulk. In such a bulk the grain contact is anticipated to be higher defined than in an ordinary ceramic bulk. The first halfmetallic homocomposite bulk was successfully fabricated for SFMO to yield excellent low-field tunneling magnetoresistance (LF-TMR) characteristics, e.g. ~5% at 0.5T at room temperature. It was found that the ratio of the smaller sized powder to the higher for the optimal LF-TMR is ~ 20%. It was considered that the nano-scale grain boundary is probably in a super-paramagnetic state yet while the grain inside is in a halfmetallic state.
(3)Halfmetallic layered oxides at room temperature
In previous sections (1) and (2) we reported discoveries of new halfmetals and development of halfmetallic bulks which show excellent LF-TMR at room temperature. None the less novel room-temperature halfmetallic layered oxides have not been obtained in this research. We believe that halfmetals of such nature are musts for spintronics and hope that further search for such halfmetals shall be continued, based on the results of the present project. Less