高压增氧T′相R_2CuO_(4+δ)(R=Nd～Tm)低温磁性研究

Magnetic Behavior of Oxygen-Doped T′-R_2CuO_4(R=Nd～Tm) at Low Temperature

T′相R2CuO4稀土铜氧化合物由于尺度效应而产生弱铁磁性行为已经被人们关注,报导了通过高温高氧压(6GPa,1000℃)合成稀土T′相R2CuO4(R=Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er和Tm)化合物的结构和磁学性能。磁化率曲线显示,在低温下所有的高压增氧R2CuO4样品都出现新的低温弱铁磁性反常行为,转变温度在28K附近。新的低温弱铁磁性行为是由于CuO2面上微量氧空穴的掺入,使处于反铁磁有序CuO2面形成局域化的铁磁性团簇造成。实验证明新发现的低温弱铁磁性行为与尺度效应产生弱铁磁性行为属于完全不同的物理机制。结果还预示T′相R2CuO4稀土铜氧化合物很难通过空穴掺杂而实现超导。

The weak ferromagnetic behavior arises from the size effects, which gives rise to the distortion of the (T′-R_2CuO_4) structure.In this paper,we study magnetic properties on rare-earth cuprates,R_2CuO_4 (R=Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er and Tm),synthesized under high oxygen pressure (6 GPa) at elevated-temperature.The magnetic susceptibility measurements show a new weak-magnetic component near a characteristic temperature of 28 K.Appearances of the low temperature weak-magnetism are independent of the rare-earth components and are a common behavior of all oxygen-doped T′-R_2CuO_4 cuprates.We argue that (1) the weak ferromagnetic behavior occurred near 28 K couldn't be attributed to the size effects,but to the formation of ferromagnetic clusters in CuO_2 planes caused by the oxygen-doping under high pressure;(2) superconductivity and weak ferromagnetism seem to be exclusive in T′-R_2CuO_4 compounds,i.e.,the ferromagnetic clusters in CuO_2 planes seems to be incompatible with superconductivity in these system.