热处理条件对BaSm_(0.3)Fe_(11.7)O_(19)铁氧体纤维结构演化和磁性能的影响

Effects of Heat-treatment Condition on Structure and Magnetic Properties of BaSm_(0.3)Fe_(11.7)O_(19) Ferrite Fibers

以金属盐和柠檬酸为原料,采用溶胶-凝胶法制备了尺寸在1μm以下具有较大长径比的BaSm0.3Fe11.7O19铁氧体纤维.采用热重-差热分析仪(TG-DSC)、X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)和振动样品磁强计(VSM)对前驱体纤维及其焙烧产物进行了表征.结果表明,在750℃焙烧1 h后,BaSm0.3Fe11.7O19铁氧体相已基本形成,随着焙烧温度的升高和保温时间的延长,BaSm0.3Fe11.7O19晶粒尺寸逐渐增大,纤维表面更加粗糙,片状结构明显.同时,纤维的饱和磁化强度(Ms)随晶粒尺寸的增大而增大,而矫顽力(Hc)则呈现先增大后减小的趋势,在晶粒尺寸为58.4 nm附近达到最大值(459.2 kA/m),表明BaSm0.3Fe11.7O19纤维的临界单畴尺寸在60 nm左右.在低温(-196℃)和室温(27℃)下样品的磁性能存在明显的差异,这主要与纳米晶的表面自旋有关.

The BaSm0.3Fe11.7O19 ferrite fibers with diameters below 1 μm were successfully fabricated by sol-gel method with metal salts and citric acid as starting reagents.The precursor and calcined products were characterized by means of thermogravimetric and differential thermal analysis（TG-DSC）,X-ray powder diffraction（XRD）,field emission scanning electron microscopy（FE-SEM） and vibrating sample magnetometer（VSM）.The results showed that the pure BaSm0.3Fe11.7O19 ferrite phase was basically formed after being calcined at 750 ℃ for 1 h.With the increase of calcination temperature and holding time,the grain growth took place,the fiber surface became much rougher and plate structure became more and more obvious.At the same time,the saturation magnetization（Ms） of BaSm0.3Fe11.7O19 ferrite fibers monotonously increased,while the coercivity（Hc） initially increased,reached a maximum value of 459.2 kA/m at a grain size of 58.4 nm,and then decreased with further grain growth,indicating that the single-domain critical size of BaSm0.3Fe11.7O19 ferrite fibers may be around 60 nm.The difference of Ms and Hc measured at 27 ℃ and-196 ℃ are attributed to the surface spin order nanocrystalline BaSm0.3Fe11.7O19 ferrite.