| Project/Area Number |
11440108
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
固体物性Ⅱ(磁性・金属・低温)
|
|---|
| Research Institution | Shimane University |
|---|
Principal Investigator |
TAKEUCHI Jun Shimane University, Interdisciplinary Faculty of Science and Engineering, Professor, 総合理工学部, 教授 (00135899)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
MIYOSHI Kiyotaka Shimane University, Interdisciplinary Faculty of Science and Engineering, Research Associate, 総合理工学部, 助手 (10294365)
FUJIWARA Kenji Shimane University, Interdisciplinary Faculty of Science and Engineering, Associate Professor, 総合理工学部, 助教授 (50238630)
|
|---|
| Project Period (FY) |
1999 – 2000
|
| Project Status |
Completed (Fiscal Year 2001)
|
| Budget Amount *help |
¥10,200,000 (Direct Cost: ¥10,200,000)
Fiscal Year 2000: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1999: ¥8,800,000 (Direct Cost: ¥8,800,000)
|
|---|
| Keywords | metal-insulator transition / spin frustration / pyrochlore oxides / electron-electron correlation / spin glass / magnetic and transport properties / パイロクロア / 磁化・電気抵抗・比熱 / 交流磁化率 |
|---|
| Research Abstract |
We have studied magnetic and transport properties of pyrochlore type R_2Mo_2O_7 (R=Y, Er-Nd) single crystals grown by a floating zone method through the measurements of DC and AC magnetic susceptibilities, electrical resistivity and specific heat. The results are summarized as follows.
1. It has been found that the systems with R=Y and Er-Tb are spin-glass-like insulators of activated type obeying ρ〜exp[Δ/ 2kT ], where the resultant energy gap Δ decreases with decreasing the lattice constant of the system. A divergent behavior of nonlinear susceptibility for the system with R=Tb, and AT- and GT-phase boundary lines for R=Y, which are typical characteristics of spin glass, have also been found.
2. The systems with R=Gd-Nd, which have larger lattice constants, have been found to show ferromagnetic ordering (Tc〜50-100 K) with metallic conductivities. Particularly for the system with R=Gd, the electrical resistivity has been found to exhibit a saturation behavior above 200 K, which is a characteristic of the systems near a Mott transition. In addition, any sharp anomaly of the specific heat around Tc has not been observed for the system with R=Gd in contrast to the systems with R=Sm and Nd.
3. For (Sm_<1-x>Tb_x)_2Mo_2O_7, it has been found that both metallic conductivity and ferromagnetic ordering appear only in the composition range below x=0.75, indicating that both properties are strongly correlated each other in this system. The effect of applying a pressure to the system with x=0.75 is a little curious. The ferromagnetism tends to be suppressed whereas the electrical resistivity is changed to be more metallic under the pressure of 0.8 GPa. The investigation of magnetic, transport and structural properties under higher pressure will be continued to clarify the mechanism of the metal-insulator transition (crossover) in these pyrochlore molybdates.
|
