Phase diagram and isotope effect in (PrEu)_0.7Ca_0.3CoO_3 cobaltites exhibiting spin-state transitions
A. V. Kalinov, O. Yu. Gorbenko, A. N. Taldenkov, J. Rohrkamp, O. Heyer, S. Jodlauk, N. A. Babushkina, L. M. Fisher, A. R. Kaul, A. A. Kamenev, T. G. Kuzmova, D.… 展开作者
A. V. Kalinov, O. Yu. Gorbenko, A. N. Taldenkov, J. Rohrkamp, O. Heyer, S. Jodlauk, N. A. Babushkina, L. M. Fisher, A. R. Kaul, A. A. Kamenev, T. G. Kuzmova, D. I. Khomskii, K. I. Kugel, T. Lorenz
备注：
13 pages, including 11 figures, to be published in Phys. Rev. B
We present the study of magnetization, thermal expansion, specific heat, resistivity, and a.c. susceptibility of (Pr$_{1-y}$Eu$_y$)$_{0.7}$Ca$_{0.3}$CoO$_3$ cobaltites. The measurements were performed on ceramic samples with $y = 0.12 - 0.26$ and $y = 1$. Based on these results, we construct the phase diagram, including magnetic and spin-state transitions. The transition from the low- to intermediate-spin state is observed for the samples with $y > 0.18$, whereas for a lower Eu-doping level, there are no spin-state transitions, but a crossover between the ferromagnetic and paramagnetic states occurs. The effect of oxygen isotope substitution along with Eu doping on the magnetic/spin state is discussed. The oxygen-isotope substitution ($^{16}$O by $^{18}$O) is found to shift both the magnetic and spin-state phase boundaries to lower Eu concentrations. The isotope effect on the spin-state transition temperature ($y > 0.18$) is rather strong, but it is much weaker for the transition to a ferromagnetic state ($y < 0.18$). The ferromagnetic ordering in the low-Eu doped samples is shown to be promoted by the Co$^{4+}$ ions, which favor the formation of the intermediate-spin state of neighboring Co$^{3+}$ ions.
Griffiths phase in solid-solution of ferromagnetic manganite and cobaltite
本文报道了在铁磁（FM）La $_{0.6}$ Sr $_{0.4}$ MnO $_3$和La $_{0.6}$ Sr $_{0.4}$ CoO $_3$的固溶体La $_{0.6}$ Sr $_{0.4}$ Mn $_{1-x}$ Co $_x$ O $_3$中，在很宽的$x$范围内存在格里菲斯相（GP）.在该化合物中，GP是由于FM背景中随机分布的Co-O-Mn反铁磁键的淬灭而产生的。与二价掺杂的锰氧化物相反，本系统中的GP可以完全以高于$T_C$的金属态存在（对于$x$ $<$ 0.10）。在此基础上绘制了磁电子相图。
A common behavior of thermoelectric layered cobaltites: incommensurate spin density wave states in [Ca$_2$Co$_{4/3}$Cu$_{2/3}$O$_4$]$_{0.62}$[CoO$_2$] and [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$]
用正μ子自旋旋转和弛豫（$μ^+$ SR）实验研究了错配层状钴酸盐[Ca $_2$ Co $_{4/3}$ Cu $_{2/3}$ O $_4$ ] $_x^{\rm RS}$ [CoO $_2$ ]（$x \sim$ 0.62，RS表示岩盐型块体）的磁性.在低于180 K（= $T_{\rm C}^{\rm on}$）时发现了向无公度（{\sf IC}）自旋密度波（{ \sf SDW}）态的跃迁;在低于140 K（= $T_{\rm C}$）时观察到了由于静态内磁场引起的明显振荡。此外，零场$μ^+$ SR实验的各向异性行为表明{ \sf IC-SDW}在$a$-$b$平面中传播，振荡力矩沿c轴定向。这些结果与相关化合物[Ca $_2$ CoO $_3$ ] $_{0.62}^{\rm RS}$ [CoO $_2$ ]{ \sl i.e.}，Ca $_3$ Co $_4$ O $_9$ .由于[Ca $_2$ Co $_{4/3}$ Cu $_{2/3}$ O $_4$ ] $_{0.62}^{\rm RS}$ [CoO $_2$ ]中的{ \sf IC-SDW}场与纯的和掺杂的[Ca $_2$ CoO $_3$ ] $_{0.62}^{\rm RS}$ [CoO $_2$ ]中的{ \sf IC-SDW}场大致相同，因此得出结论，{ \sf IC-SDW}存在于[CoO $_2…
Transport properties and magnetic field induced localization in the misfit cobaltite [Bi$_2$Ba$_{1.3}$K$_{0.6}$Co$_{0.1}$]$^{RS}$[CoO$_2$]$_{1.97}$ single crystal
系统地研究了[Bi $_2$ Ba $_{1.3}$ K $_{0.6}$ Co $_{0.1}$ ] $^{RS}$ [CoO $_2$ ] $_{1.97}$单晶在磁场下的电阻率、热电势和霍尔系数。面内电阻率（$ρ_{ab}$（T））显示出低至2K的金属行为，其中$T^2$依赖性低于30 K;而面外电阻率（$ρ_{c}(T)$）显示出高温下的金属行为和低于约12 K的热活化半导体行为。显著的特点是低温下磁场诱导$ρ_{ab}$和$ρ_{c}(T)$的ln（1/ $T$）发散行为。基于多带电子结构的公式可以很好地拟合正磁阻效应。在$ρ_{ab}$和$ρ_{c}(T)$中的ln（1/ $T$）发散行为可能源于磁场诱导的二维弱局域化或自旋密度波。
Coexistence of magnetic and dielectric glassy states in alternating kagome and triangular lattice LuBaCo$_4$O$_7$ cobaltite
Indian Institute of Technology Bombay（印度理工学院孟买分校）；National Sun Yat-sen University（国立中山大学）；Center of Crystal Research, National Sun Yat-sen University（国立中山大学晶体研究中心）；Indian Institute of Science（印度科学研究所）；Indian Institute of Technology, Kharagpur（印度理工学院卡拉格普尔分校）；Tilk Manjhi Bhagalpur University（蒂尔克曼吉巴加尔布尔大学）
Magnetic-field-induced spin crossover of Y-doped Pr$_{0.7}$Ca$_{0.3}$CoO$_{3}$
最近发现空穴掺杂的Pr基钙钛矿钴酸盐Pr $_{0.5}$ Ca $_{0.5}$ CoO $_{3}$和（Pr $_{1-y}$ RE $_{y}$）$_{0.3}$ Ca $_{0.7}$ CoO $_{3}$（其中RE是稀土）的家族表现出同时的金属-绝缘体、自旋态和价态转变。我们研究了磁场诱导的相变（Pr $_{1-y}$ Y $_{y}$）$_{0.7}$钙$_{0.3}$ CoO $_{3}$的磁化强度测量在4.2 $-$ 100 K的140 T的磁场与$y$ = 0.0625，0.075，0.1变化的化学压力。所观察到的磁场诱导的转变被发现同时发生的金属-绝缘体转变高达100 T。用单离子自旋交叉模型分析了所得到的磁场-温度（$B$-$T$）相图和磁化曲线。另一方面，化学压力依赖性的实验获得的磁化强度变化在相变过程中不同意与单离子模型接近低温时。在低温下的磁化强度变化的显着$y$依赖性可能是由于在顺磁金属相中Co $^{3+}$的巡回磁性，其中化学压力通过促进双交换相互作用增强了交换分裂。所观察到的（Pr $_{1-y}$ Y $_{y}$）$_{0.7}$ Ca $_{0.3}$ CoO $_{3}$的$B$-$T$相图与LaCoO $_{3}$的$B$-$T$相图完全相反，表明在（Pr $_{1-y}$ Y $_{y}$）$_{0.7}$ Ca $_{0.3}$ C…
