NiFe_2O_4纳米固体的穆斯堡尔谱研究

MSSBAUER SPECTROSCOPY STUDY OF NiFe 2O 4 NANOSOLID COMPACTED UNDER HIGH PRESSURE

利用反滴共沉淀法制备了ＮｉＦｅ２Ｏ４纳米粒子，并在高压下（４５ＧＰａ）压制成块状纳米固体材料．Ｘ射线衍射显示，ＮｉＦｅ２Ｏ４纳米固体的晶体结构和平均晶粒尺寸在高压下均没有发生变化．但其室温和低温穆斯堡尔谱结果表明，高压对纳米固体内部的磁相互作用和界面原子状态有很大的影响．在高压下，纳米固体内部的颗粒间磁偶极相互作用和界面离子间的超交换相互作用显著增强．从而明显抑制了ＮｉＦｅ２Ｏ４纳米固体的超顺磁弛豫，并降低了纳米固体的磁各向异性常量．通过对ＮｉＦｅ２Ｏ４纳米固体的穆斯堡尔谱的分析，还可以得到有关高压下纳米固体表面和界面区域内铁原子的配位氧四面体和氧八面体的形成信息．随着压力的增加，这些配位氧多面体逐渐形成，其对称性和近程有序性都逐渐增强．使得ＮｉＦｅ２Ｏ４纳米固体的界面原子排列的有序程度在高压下也逐渐增强，表现出向大尺寸多晶固体的晶界结构转变的趋势．

NiFe 2O 4 nanoparticles with on average grain size of 12nm were compacted into nanosolids under the pressure of 0 0—4 5GPa.The Mssbauer spectra of NiFe 2O 4 nanosolids at room temperature and low temperatures show that high pressure has a strong influence on the magnetic interaction and interface atomic state inside the nanosolid,though the crystal structure and average grain size of nanosolid do not change under high pressure.Under high pressure,the superparamagnetic relaxation of NiFe 2O 4 nanosolid is suppressed obviously by the enhancement of the interparticle magnetic dipole interaction and the superexchange interaction among the interface ions in the nanosolid,and the magnetic anisotropy of it is also weakened by the interparticle magnetic coupling in it.At the same time,the symmetry and the degree of short range order of the polyhedrons are raised gradually with the increase of pressure,and then the atomic structure in the surface and interface zone of NiFe 2O 4 nanosolid shows a tendency to change into the grain boundary structure of common polycrystalline solid with large grain size.