从自旋冰到自旋液态的渡越--结构与磁性质的演化

Transition from spin ice to spin liquid——evolvement of structure and magnetic properties

使用固相反应法得到了Ho2-xTbxTi2O7(x=0,0·5,1,1·5,2)系列多晶样品.X射线衍射(XRD)实验与2K到300K温度区间的直流磁化率测量结果显示,随着Tb即是x的增加,体系由自旋冰Ho2Ti2O7向自旋液Tb2Ti2O7渡越,立方烧绿石结构的晶格常数逐渐增加,居里常数和有效磁矩逐渐减小,特别是居里-外斯温度由Ho2Ti2O7大于零的铁磁性,向小于零的反铁磁性转变.深入的分析揭示随Ho2-xTbxTi2O7中x的增加,体系的长程偶极相互作用强度Dnn逐渐减小.铁磁或反铁磁、以及长程磁偶极相互作用的强弱可能是体系成其为自旋冰或耦合顺磁-自旋液行为的两个关键因素.

The polycrystal samples of Ho_2-xTb_xTi_2O_7（x=0,0.5,1,1 .5,2） were prepared by solid reaction method. The result of X-ray diffraction （XRD） and dc susceptibility measurement from 2 K to 300 K both indicate that as the content of Tb^3＋,i.e. x,increases,the system crosses over from Ho_2Ti_2O_7spin ice to Tb_2Ti_2O_7 spin liquid,the lattice constant of cubic pyrochlore increases,while the Curie constant and effective magnetic moment decrease. Especially,the Curie-Weiss temperature decreases from positive to negative with the decrease of x,implying the transition from ferromagnetic Ho_2Ti_2O_7 to anti-ferromagnetic Tb_2Ti_2O_7. The detailed analysis shows that as x in Ho_2-xTb_xTi_2O_7 increases,the intensity of long-range dipolar interaction D_nn decreases. Being ferromagnetic or anti-ferromagnetic,and the change in intensity of long-range dipolar interaction, may be the two crucial factors influencing on the system to form spin ice state or cooperative paramagnetic state,i.e. the spin liquid state.