Institute of Physics ASCR, Prague 6, Czech Republic.
J Phys Condens Matter. 2013 May 29;25(21):216006. doi: 10.1088/0953-8984/25/21/216006. Epub 2013 May 3.
The electric, magnetic, and thermal properties of three perovskite cobaltites with the same 30% hole doping and ferromagnetic ground state were investigated down to very low temperatures. With decreasing size of large cations, the ferromagnetic Curie temperature and spontaneous moments of cobalt are gradually suppressed: TC = 130 K, 55 K and 25 K and m = 0.68 μB, 0.34 μB and 0.23 μB for Nd0.7Sr0.3CoO3, Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO3, respectively. The moment reduction with respect to the moment of the conventional ferromagnet La0.7Sr0.3CoO3 (T(C) = 230 K, m = 1.71 μB) in the so-called low spin/intermediate spin (IS/LS) state for Co(3+)/Co(4+) was originally interpreted using a phase-separation scenario. Based on the present results, mainly the analysis of the Schottky peak originating from Zeeman splitting of the ground-state Kramers doublet of Nd(3+), we find, however, that the ferromagnetic phase in Nd0.7Ca0.3CoO3 and likely also in Pr0.7Ca0.3CoO3 is uniformly distributed over the whole sample volume, despite the severe drop of moments. The ground state of these compounds is identified with the LS/LS-related phase derived theoretically by Sboychakov et al (2009 Phys. Rev. B 80 024423). The ground state of Nd0.7Sr0.3CoO3 with an intermediate cobalt moment is inhomogeneous due to competition between the LS/LS and IS/LS phases. In the theoretical part of the study, the crystal field split levels for 4f(3) (Nd(3+)), 4f(2) (Pr(3+)) and 4f(1) (Ce(3+) or Pr(4+)) are calculated and their magnetic characteristics are presented.
三种具有相同 30%空穴掺杂和铁磁基态的钙钛矿钴酸盐的电性、磁性和热性能在极低温度下进行了研究。随着大阳离子尺寸的减小，钴的铁磁居里温度和自发矩逐渐受到抑制：TC = 130 K、55 K 和 25 K，m = 0.68 μB、0.34 μB 和 0.23 μB，分别为 Nd0.7Sr0.3CoO3、Pr0.7Ca0.3CoO3 和 Nd0.7Ca0.3CoO3。与传统铁磁体 La0.7Sr0.3CoO3（T(C) = 230 K，m = 1.71 μB）相比，在所谓的低自旋/中间自旋（IS/LS）状态下 Co(3+)/Co(4+)的磁矩降低最初用相分离情景来解释。基于目前的结果，主要是对源自 Nd(3+)基态 Kramers 二重态塞曼分裂的肖特基峰的分析，我们发现，然而，Nd0.7Ca0.3CoO3 中的铁磁相以及可能在 Pr0.7Ca0.3CoO3 中，尽管磁矩急剧下降，但整个样品体积中均匀分布。这些化合物的基态被确定为 Sboychakov 等人（2009 年 Phys. Rev. B 80 024423）理论上得出的 LS/LS 相关相。具有中间钴磁矩的 Nd0.7Sr0.3CoO3 的基态由于 LS/LS 和 IS/LS 相之间的竞争而不均匀。在研究的理论部分，计算了 4f(3)（Nd(3+)）、4f(2)（Pr(3+)）和 4f(1)（Ce(3+)或 Pr(4+)）的晶场分裂能级，并给出了它们的磁性特征。
