2004 Fiscal Year Final Research Report Summary
Study on high-frequency dielectric anomaly in charge ordering
| Project/Area Number |
15540348
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Condensed matter physics II
|
|---|
| Research Institution | Osaka Prefecture University |
|---|
Principal Investigator |
NOGUCHI Satoru Osaka Prefecture University, Graduate School of Engineering, Associate Professor, 工学研究科, 助教授 (70180718)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
ISHIDA Takekazu Osaka Prefecture University, Graduate School of Engineering, Professor, 工学研究科, 教授 (00159732)
KAWAMATA Shuichi Osaka Prefecture University, Graduate School of Engineering, Lecturer, 工学研究科, 講師 (50211868)
|
|---|
| Project Period (FY) |
2003 – 2004
|
| Keywords | charae order transition / electromagnetic response / dielectric anomaly / micro-wave frequency / manganese / cobaltite |
|---|
| Research Abstract |
1)Electromagnetic response of Pr_<0.5>Ca_<0.5>MnO_<3-δ> at 34 GHz was measured by a cavity perturbation method in the temperature range from 4.2 to 270 K under the magnetic field up to 12 T in order to investigate the high frequency dielectric anomaly with charge ordering.
2)The single crystals were grown by a floating zone method.
3)B-T phase diagram was determined from the magnetization and magnetoresistance measurements using a pulsed magnet.
4)When the sample is placed at the electric field maximum E_<max> in the TE_<011> mode of cylindrical cavity, the microwave amplitude shows a broad peak and a sharp peak around the CO transition as a function of field. The resonant frequency shows a minimum at a sharp peak in amplitude as a function of field. These are considered as the dielectric anomalies related to a redistribution of charges at the transition.
5)The B-T phase diagram estimated from the electromagnetic response is obtained for the first time. It is similar to that from the magnetization measurements, which suggests that the microwave dielectric response is not critically important to alter the profile of the B-T phase diagram.
6)The shift of resonant frequency from an insulator to a metal phase shows an opposite change to that usually observed in a metal-insulator transition. This may lead to the semiconducting temperature dependence in microwave conductivity with activation energy of 25 meV at high field region, where the dc resistance shows metallic temperature dependence.
7)Additional study was performed in a cobaltite by the magnetoresistance measurements with interest in the charge separation of Co ions. Colossal magnetoresistance was observed in Ca_<3-x>Y_xCo_4O_9 system, which evidences for the charge separation explained by a tunneling magnetoresistance effect as usually observed in granular magnetic films.
|
