Centro Brasileiro de Pesquisas Fisicas-CBPF, Rua Dr Xavier Sigaud 150, Urca, Rio de Janeiro, RJ, Brazil.
J Phys Condens Matter. 2010 Jun 16;22(23):236003. doi: 10.1088/0953-8984/22/23/236003. Epub 2010 May 21.
The low temperature magnetization, specific heat, electrical resistance and magnetoresistance have been studied for the Ru-doped La(1.32)Sr(1.68)Mn(2 - y)Ru(y)O(7) (y = 0.0, 0.04, 0.08 and 0.15) layered manganite system. The undoped compound (y = 0.0) shows a sharp ferromagnetic transition (T(C)) accompanied by a metal-insulator transition (T(MI)) at 118 K. The Ru substitution decreases the T(C) and T(MI) temperatures significantly. The temperature dependence of specific heat measurement confirms the decrease in T(C) by observing the anomaly corresponding to T(C). The decreased effective moments from 3.48 μ(B) for the undoped compound to 1.82 μ(B) for the highly doped compound at 5 K indicates the Ru substitution weakens the ferromagnetic order in the low temperature regime and reduces the number of Mn pairs in the highly doped sample. The field dependence of magnetization measurements exhibits an enhancement of the coercive field with increased Ru concentration and gives evidence for the mixed magnetic phase for the highly doped compound. For the undoped sample, a large negative magnetoresistance of 300% at T(C) and 128% at 4.2 K in a 5 T field were observed. The magnetoresistance ratio decreases gradually with increasing Ru substitution. We find that the doped Ru in the Mn site drives the layered manganite system towards a magnetically mixed state. The effects of Ru doping in the transport and magnetic properties will be explained by the antiferromagnetically coupled Ru and Mn sublattices.
低温磁化率、比热、电阻和磁电阻已经被研究过了，用于 Ru 掺杂的 La(1.32)Sr(1.68)Mn(2 - y)Ru(y)O(7)（y = 0.0、0.04、0.08 和 0.15）层状锰氧化物系统。未掺杂的化合物（y = 0.0）表现出尖锐的铁磁转变（T(C)），伴随着 118 K 的金属-绝缘体转变（T(MI)）。Ru 取代显著降低了 T(C)和 T(MI)温度。比热测量的温度依赖性通过观察对应于 T(C)的异常来证实 T(C)的降低。从未掺杂化合物的 3.48 μ(B)到高掺杂化合物的 1.82 μ(B)的有效磁矩的降低表明 Ru 取代在低温下削弱了铁磁序，并减少了高掺杂样品中 Mn 对的数量。磁化强度测量的磁场依赖性表现出随 Ru 浓度增加而增强的矫顽场，并且为高掺杂化合物的混合磁相提供了证据。对于未掺杂的样品，在 5 T 磁场中，在 T(C)处观察到 300%的大负磁电阻和在 4.2 K 处的 128%的大负磁电阻。随着 Ru 取代的增加，磁电阻比逐渐降低。我们发现，Mn 位掺杂的 Ru 使层状锰氧化物系统向磁混合状态发展。Ru 掺杂对输运和磁性能的影响将通过反铁磁耦合的 Ru 和 Mn 亚晶格来解释。
