多铁材料MnSb_(2)O_(6)中自旋涨落的ESR研究

Electron spin resonance study of spin fluctuation in multiferroic MnSb_(2)O_(6)

具有手性晶体结构的MnSb_(2)O_(6)其基态为螺旋磁序,对外磁场有着响应丰富的铁电性.本文通过助熔剂法制备了高质量MnSb_(2)O_(6)单晶.电子自旋共振谱(ESR)的结果表明其共振场具有类似铁磁材料的各向异性温度依赖关系.这一结果表明MnSb_(2)O_(6)基态的螺旋磁序在外磁场中形成了随磁场方向转动的圆锥磁序相(conical phase).对共振峰半高宽的进一步拟合得到一个意外小的临界指数,这表明MnSb_(2)O_(6)中的磁矩具有二维特征并且存在着较强的竞争相互作用.

The magnetic materials with a chiral crystallographic lattice have hold neither inversion center nor mirror plane,leading to the emergence of Dzyaloshinskii-Moriya interaction and exotic physical phenomena like skyrmion,multiferroicity,and chiral solition lattice.The trigonal oxide MnSb_(2)O_(6) is recognized as a novel chiral-lattice helimagnet with unusual multiferroic properties,where magnetic field enables the selecting of a single ferroelectric domain and a slight tilting of field direction can trigger the reversal of electric polarization.Single crystal of MnSb_(2)O_(6) is prepared by the flux method.The magnetic susceptibility at 2 K shows a linear field dependent behavior except in the low field region.The magnetization shows a deviation from linearity at around 0.2 T for H⊥c,while a step-like anomaly is observed at about 1 T for H//c,suggesting the domain selection and spin-flop transition,respectively.The electron spin resonance parameters,such as the resonance field,the g-factor and the linewidth DH,are obtained by performing single Lorentzian line.Interestingly,the resonance field shows a distinct,anisotropic temperature dependent behavior when further cooling,the resonance field shifts towards the lower field direction for H⊥c,while it shifts towards higher field direction for H//c.Excluding several mechanisms for this FM-like temperature dependent behavior of the resonance field,combining the ground state of spiral phase and its unique multiferroic properties,we suggest that the spiral magnetic structure of the ground state of MnSb_(2)O_(6) forms a conical magnetic structure under external magnetic field.Based on this,we can speculate the variation of ferroelectric polarization intensity with moderate and higher magnetic field.Moreover,the critical fitting of the ESR linewidth gives an unusual small critical index,p=0.49 for H⊥c and p=0.54 for H//c,implying that the magnetism possesses a two-dimensional characteristic and competitive interaction.