Sr_2CoO_(4-δ)薄膜中的自旋玻璃态的磁性质研究

Glassy magnetic behaviors in oxygen-deficient Sr_2CoO_(4-δ) films

用脉冲激光沉积方法(PLD)在铝酸镧衬底上制备了c取向的高氧空位含量的锶钴氧薄膜.X射线衍射分析表明薄膜单一取向且没有明显杂相.原位的高气压反射式高能电子衍射仪(RHEED)监测显示,薄膜为层状生长.通过对薄膜磁化强度随温度、磁场及时间的变化曲线进行测量,发现零场冷曲线上可能存在两个特征温度:Tf和Ta.Tf为对应玻璃态的冻结温度而Ta对应少量的不缺氧锶钴氧团簇沿c轴的各项异性场的特征温度.磁弛豫、记忆效应和磁滞回线等进一步研究均表明体系中主要成分更可能是自旋玻璃,且在冻结温度之上自旋玻璃即开始了冻结.较高缺氧样品引入的三价钴离子和体系原有的四价钴离子共存,两者的共同效果形成了双交换和超交换作用的竞争,从而导致了系统复杂的自旋玻璃行为.

We have fabricated c-axis-oriented Sr2CoO4-δ thin films under relatively low oxygen pressure by the pulsed laser deposition method （PLD） on LaAlO3 substrates. X-ray diffraction and high-pressure reflection high energy electron diffraction （RHEED） demonstrate that the films were well deposited. There exist two different characteristic temperatures, Tf and Ta,in the ZFC curve of temperature dependence of magnetization. Tf may correspond to the freezing temperature while Ta may be related with the anisotropic field of c-axis. Further investigations including magnetic relaxation,memory effect and hysteresis behaviour measurements suggest a main phase of spin glass,which starts the frozen-in process even above the freezing temperature. We ascribe the spin glass behaviour to the competition betwcen double-exchange and super-exchange interactions which could have originated from the coexistence of Co4 ＋ and Co3 ＋ caused by oxygen deficiency in the films.