Phase Diagram and Dynamics of Dipolar Spin Ice in Tilted [111] Field

• Main Authors: Chun-Chu Cheng, 鄭君筑
• Other Authors: 高英哲
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/s55fff

碩士 === 國立臺灣大學 === 物理學研究所 === 105 === In this thesis, we study the behavior of Dysprosium Titanate (Dy_2Ti_2O_7) ,one of the well established spin ice materials, in the tilted magnetic field numerically. Spin ice has attracted much attention in frustrated systems because it is the magnetic analogue to the water ice system. The frustration leads to the degenerate ground states and the residual entropy which appears in both spin ice and water ice. The ground state degeneracy can be lifted by applying magnetic field. An ordered state, q=X state, was found previously when applying a magnetic field along [111] direction with slightly tilt toward [112] direction in a numerical study of dipolar spin ice model. In this thesis, we extended our model to generalized dipolar spin ice model by adding further-neighbor interactions. The extra second- and third-nearest neighbor exchange interactions also support the existence of q=X state but shift the boundary value of the magnetic field along [111] direction. Also, in certain parameter space of further-neighbor interactions, antiferromagnetic spin chain ordering of q=X state on Kagome plane is suppressed and fully polarized state appears instead. We also study the dynamics of spin ice in tilted [111] field near transition where ordering of spin chains on Kagome plane start to be broken by the thermal fluctuation. By numerically measuring the AC susceptibility, we find the dynamics along two perpendicular directions on Kagome plane are different.