低温固相反应法制备的NiFe_2O_4纳米颗粒的结构与磁性

Structure and magnetic properties of NiFe_2O_4 nanoparticles prepared by low-temperature solid-state reaction

采用低温固相反应法制备了晶粒尺寸在8—47nm之间的NiFe2O4纳米颗粒系列样品,用X射线衍射仪(XRD)、高分辨中子粉末衍射谱仪、振动样品磁强计和超导量子干涉仪等对样品的晶体结构、宏观磁性和纳米颗粒的表面各向异性进行了分析研究.XRD和中子衍射测量结果显示纳米颗粒的晶格常数略高于块体材料,样品的氧参量表明纳米颗粒的晶格畸变程度没有块体材料严重.相对块体材料,纳米颗粒具有较小的磁化强度、较大的矫顽力和各向异性能密度.纳米颗粒从多畴转变为单畴的临界尺寸约为40nm,超顺磁性临界尺寸约为16nm.

NiFe2O4 nanopartiele series samples in the grain size range of 8--47 nm were successfully synthesized by low-temperature solid-state reaction. The X-ray diffraetometer （XRD）, HRPT neutron powder diffraetometer, vibrating sample magnetometer （VSM） and superconducting quantum interference devices （SQUID） were used to characterize the structure, magnetic properties and surface anisotropy of nanopartieles. Data of XRD and neutron diffraction showed that the lattice constants of NiFe2O4 nanopartieles were lager than that of the bulk counterpart. Oxygen parameters suggested that lattice distortion were decreased with reduced particle sizes. In comparison with the bulk material, smaller magnetization, larger coercive force and anisotropy energy density for nanopartieles were observed. The critical sizes for transition from muhidomain to single domain and for superparamagnetie transition were estimated to be 40 nm and 16 nm, respectively.