Charge state modification in Mn site substituted CMR manganites: strong deleterious influence on the ferromagnetic–metallic state
Charge state modification in Mn site substituted CMR manganites: strong deleterious influence on the ferromagnetic–metallic state
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DOI：
10.1088/0953-8984/19/23/236207
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发表时间：
2007-06
期刊：
影响因子：
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通讯作者：
L. Seetha Lakshmi;K. Dörr;K. Nenkov;V. Sastry;K. Müller
中科院分区：
文献类型：
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作者：
L. Seetha Lakshmi;K. Dörr;K. Nenkov;V. Sastry;K. Müller
报告了 Mn 位点电荷态改变对 CMR 亚锰酸盐物理性质的影响。为了避免局域自旋耦合效应的额外复杂性，La0.67Ca0.33MnO3 的 Mn 位点替换是用不同价态的适当反磁性离子 Zn2+、Zr4+、Ta5+ 和 W6+ 进行的。取代导致晶胞尺寸变化并增强局部结构畸变，其按 Zn、Zr、Ta 和 W 的顺序增加。低于取代基的某个临界浓度 xc 时，基态是铁磁金属，超过该浓度，磁性基态表现出玻璃态行为。相变温度（TMI 和 Tc）随着取代而降低，但程度不同。对于 Ta5+ 和 W6+ 取代的化合物，观察到的居里温度 Tc 抑制率分别为 ∼39 K/at.% 和 ∼45 K/at.%，这是 Mn 位点取代的 CMR 锰酸盐中报道的最高的。除了由于增加（减少）Mn3+浓度和增强局部结构效应而改变多数载流子浓度之外，取代基的局部静电势似乎有助于巡回铁磁性和观察到的玻璃态的异常强烈的减少。
The effect of charge state modification at the Mn site on the physical properties of CMR manganites is reported. With a view to avoiding additional complexity of local spin coupling effects, Mn site substitution of La0.67Ca0.33MnO3 is carried out with appropriate diamagnetic ions—Zn2+, Zr4+, Ta5+ and W6+—of different valence states. The substitution results in size changes of the unit cell and enhanced local structural distortions, which increase in the order Zn, Zr, Ta and W. The ground state is ferromagnetic–metallic below a certain critical concentration xc of the substituents, beyond which the magnetic ground state shows a glassy behaviour. The phase transition temperatures (TMI and Tc) decrease with substitution, but to different extents. The observed suppression rates of the Curie temperature, Tc, of ∼39 K/at.% and ∼45 K/at.% respectively for Ta5+ and W6+ substituted compounds are the highest reported in the Mn site substituted CMR manganites. Besides the modification of majority carrier concentration due to the increased (decreased) Mn3+ concentration and enhanced local structural effects, the local electrostatic potential of the substituents seems to contribute to the unusually strong reduction in the itinerant ferromagnetism and the observed glassy states.