Transport and magnetic studies on the spin state transition of Pr1-xCaxCoO3 up to high pressure
Transport and magnetic studies on the spin state transition of Pr1-xCaxCoO3 up to high pressure
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DOI：
10.1143/jpsj.73.1987
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发表时间：
2004-07-01
影响因子：
1.7
通讯作者：
Takata, M
中科院分区：
文献类型：
--
作者：
Fujita, T;Miyashita, T;Takata, M
在常压和高压下对（Pr_（1-y）R ′（y））（1-x）A（x）CoO（3）[R ′ =（稀土元素和Y）; A =（Ca，Ba和Sr）]进行了输运和磁性测量、结构和NMR研究。随着温度T的降低，该系统表现出从近金属态到绝缘态的相变，其中Co 3+的低自旋（LS）态突然稳定。对于y = 0，我们绘制了不同外压p值下的T-x相图。它表明，低温相的（T，x）区（在常压下，它被限制在x = 0.5附近的一个很窄的区域内）随着p的增加而扩大。对于转变的发生，Pr和Ca原子似乎都是必要的。讨论了Co ~（3+）离子周围的局域结构与Co ~（3+）离子的电子（或自旋）态之间的密切关系：CoO_6八面体的晶胞体积或体积越小，八面体的倾斜角越大，转变温度越高。还讨论了由A原子掺杂引入的载流子的作用。通过对Pr_（1-x）Ca_xCoO_3的~（59）Co核磁共振谱和磁化率的分析，粗略估计了Co ~（3+）和Co ~（4+）不同自旋态之间的电子能量分离。
Transport and magnetic measurements and structural and NMR studies have been carried out on (Pr1-yR'(y))(1-x)A(x)CoO(3) [R' = (rare earth elements and Y); A = (Ca, Ba and Sr)] at ambient pressure and high pressure. The system exhibits a phase transition from a nearly metallic to an insulating state with decreasing temperature T, where the low spin (LS) state of Co3+ is suddenly stabilized. For y = 0, we have constructed a T-x phase diagram at various values of the external pressure p. It shows that the (T, x) region of the low temperature phase, which is confined to a very narrow region around x = 0.5 at ambient pressure, expands as p increases. For the occurrence of the transition, both the Pr and Ca atoms seem to be necessary. The intimate relationship between the local structure around the Co ions and the electronic (or spin) state of Co3+ ions is discussed: For the smaller unit cell volume or the smaller volume of the CoO6 octahedra and for the larger tilting angle of the octahedra, the temperature of the transition becomes higher. The role of the carriers introduced by the doping of the A atoms, is also discussed. By analyzing Co-59-NMR spectra and magnetic susceptibility of Pr1-xCaxCoO3, the electronic-energy-separations among the different spin states of Co3+ and Co4+ are roughly estimated.