单一晶相氧化锰纳米颗粒的交换偏置效应

本文利用高温油相法制备出尺寸、形状均一的 MnO纳米颗粒, X射线衍射图 (XRD) 和透射电子显微镜 (TEM) 照片清晰表明MnO纳米颗粒为单一的面心立方岩盐晶体结构, 尺寸为15nm, 粒径分布很窄. 通过零场冷却 (ZFC) 和带场冷却 (FC)的磁滞回线发现MnO纳米颗粒具有明显的交换偏置效应, 而且磁滞回线同时表现出横向和纵向偏移. 横向偏移说明纳米颗粒中两相复合的存在, 纵向偏移说明了存在自旋玻璃相或者超顺磁相. 进而通过不同频率下随温度变化的交流磁化率的测定, 根据Mydosh的经验数值确认 MnO纳米颗粒表面层为自旋玻璃相, 并得到 MnO纳米颗粒表面自旋玻璃相的转变温度为T_SG=32K.关键词：纳米颗粒氧化锰交换偏置自旋玻璃

Exchange bias effect in single crystalline phase MnO nanoparticles

The MnO nanoparticles with uniform size (～15 nm) and shape have been synthesized in an inert atmosphers by high-temperature oil phase method. XRD patterns and HRTEM reveals that the as-synthesized MnO nanoparticles are of pure crystalline phase. TEM image shows that the MnO nanoparticles are in spherical shape with a narrow size distribution. Both oil phase and the nanoparticles protected with inert gas in the synthesis process can avoid the oxidization of Mn²⁺. The obvious exchange bias effect can be observed from the M-H loop of MnO nanoparticles under zero field cooling (ZFC) and FC measurements. Furthermore, the temperature-dependent AC susceptibility of the MnO nanoparticles reveals that the exchange bias effect originates from the antiferromagnetic MnO core and the spin-glass surface, rather than the superparamagnetic phase.
Keywords：nanoparticlesMnOexchange biasspin glass