溶胶-凝胶法制备的Zn_1-xCo_xO晶体粉末的结构和磁性行为

来源期刊：金属学报2011年第3期

论文作者：高茜 孙本哲 祁阳 齐连仲

文章页码：337 - 343

关键词：溶胶-凝胶法； Zn_1-xCo_xO； 室温铁磁性

Key words：sol-gel technique； Zn_1-xCo_xO； room temperature ferromagnetism

摘    要：利用溶胶凝胶法制备了Zn_1-xCo_xO(x=0.01-0.05,原子分数)纳米晶体粉末,利用XRD,TEM和SEM对其结构、结晶状态、形貌和成分进行了表征和分析.结果表明,所有样品均由尺寸约为100 nm的晶体颗粒组成,Zn_1-xCo_xO的晶格常数均比未掺杂的ZnO晶格常数小,且保持了单一纤锌矿ZnO结构,实际掺杂浓度与名义掺杂浓度基本匹配.振动样品磁强计测试结果显示,所有样品都具有室温铁磁性.结合微结构,确定该铁磁性为材料的本征属性,并推断O空位是铁磁交换作用的媒介,晶粒度的大小也影响了样品的磁性行为.

Abstract: ZnO-based diluted magnetic semiconductors (DMSs) have been considered as one of the promising candidates for fabricating DMSs due to their initial prediction in theory of having the Curie temperature greater than room temperature,its high solubility for transition metals,and its superior semiconductor properties.Recently,Co substituted ZnO DMSs were reported frequently to show ferromagnetic properties at room temperature.However,various subsequent studies do not seem to converge on the origin of room-temperature ferromagnetism.Among the controversy,Co-cluster, Co-oxides and substitutions of Co for Zn are typical viewpoints.Meanwhile,it is not completely understood how the fabricating process influence the magnetic properties of Co-doped ZnO DMS.For this purpose,relationships among Co-doping concentration,sintered temperature,microstructure and magnetic properties of ZnO need to be invesigated particularly.In this paper,Zn_1-xCo_xO (x=0.01, 0.02,0.03,0.04 and 0.05,atomic fraction) nanocrystal powders were prepared by sol-gel technique.The crystal structure,lattice parameters,morphology and composition were characterized and analyzed by XRD,TEM,SEM and EDS,respectively.The magnetic properties were examined at room temperature using a vibrating sample magnetometer (VSM).It can be found that all the samples are composed of the particles with hexagonal wurtzite structure and the sizes of the particles are about 100 nm.For all synthesized Zn_1-xCo_xO samples,the lattice constants are smaller than those of un-doping ZnO crystals under the condition of the same sintered temperature.It indicates Co²⁺ ions have substituted Zn²⁺ sites.All the samples exhibit room-temperature ferromagnetic characteristics,and the ferromagnetism is their intrinsic attribute,in which the Zn_0.98Co_0.02O sample sintered at 500 and 700℃ has the highest coercivity(H_c) of 334.02 Gs and the highest remanent magnetization ratio (M_r/M_s) of 0.1813, respectively,and the Zn_0.96Co_0.04O sample sintered at 950℃ has the maximum magnetic energy product (BH) of 1.7604×10^-4J/kg and saturation magnetization (M_s) of 0.5583 Am²/kg.The magnetic behaviors of these samples vary not only with the concentration of Co,but also with the size of crystal grains and the concentration of oxygen vacancies.It can be found that the moderate Co content and the larger size of crystal grains are in favour of increasing room-temperature ferromagnetic characteristics. Meanwhile,as far as the same concentration of Co is concerned,the smaller volume of the cell contributes to increase room-temperature ferromagnetism.