Er2Ti2O7和Tb2Ti2O7在极低温下的磁化过程
Magnetisation process in Er2Ti2O7 and Tb2Ti2O7 at very low temperature
摘要：
我们提出了一个模型，占在很低的温度下的高场磁化强度在两个烧绿石受挫系统，Er 2 Ti 2 O 7和Tb 2 Ti 2 O 7。这两种化合物呈现出非常不同的基态：Er_2Ti_2O_7具有平面晶场各向异性，是反铁磁体，T_N=1.2K，而Tb_2Ti_2O_7具有Ising特征，在0.05K以下没有磁有序，因此被称为"自旋液体“。我们的模型是一个平均场自洽计算涉及的4个稀土网站的四面体，建筑单位的烧绿石晶格。它包括全晶场哈密顿量，无限范围偶极相互作用和各向异性最近邻交换三分量张量描述。对于Er 2 Ti 2 O 7，我们讨论了我们的治疗的交换张量的等价性，采取对角线在一个框架中连接到一个稀土-稀土键，与最近开发的Kramers双峰在烧绿石晶格的伪自旋哈密顿。在Tb_2Ti_2O_7中，我们模型的一个重要组成部分是在很低的温度下发生对称性破缺。我们比较它的预测等温磁化强度与“量子自旋冰”模型。
英文摘要：
We present a model which accounts for the high field magnetisation at very low temperature in two pyrochlore frustrated systems, Er2Ti2O7 and Tb2Ti2O7. The two compounds present very different ground states: Er2Ti2O7, which has a planar crystal field anisotropy, is an antiferromagnet with T_N=1.2K, whereas Tb2Ti2O7 is expected to have Ising character and shows no magnetic ordering down to 0.05K, being thus labelled a ``spin liquid''. Our model is a mean field self-consistent calculation involving the 4 rare earth sites of a tetrahedron, the building unit of the pyrochlore lattice. It includes the full crystal field hamiltonian, the infinite range dipolar interaction and anisotropic nearest neighbour exchange described by a 3-component tensor. For Er2Ti2O7, we discuss the equivalence of our treatment of the exchange tensor, taken to be diagonal in a frame linked to a rare earth - rare earth bond, with the pseudo-spin hamiltonian recently developped for Kramers doublets in a pyrochlore lattice. In Tb2Ti2O7, an essential ingredient of our model is a symmetry breaking developping at very low temperature. We compare its prediction for the isothermal magnetisation with that of ``the quantum spin ice'' model.
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