Molavian H R, Gingras M J P
Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
J Phys Condens Matter. 2009 Apr 29;21(17):172201. doi: 10.1088/0953-8984/21/17/172201. Epub 2009 Mar 20.
Despite a Curie-Weiss temperature θ(CW)∼-14 K, the Tb(2)Ti(2)O(7) pyrochlore magnetic material lacks long range magnetic order down to at least T(*)≈50 mK. It has recently been proposed that the low temperature collective paramagnetic or spin liquid regime of this material may be akin to a spin ice state subject to both thermal and quantum fluctuations-a quantum spin ice (QSI) of sorts. Here we explore the effect of a magnetic field B along the [111] direction on the QSI state. To do so, we investigate the magnetic properties of a microscopic model of Tb(2)Ti(2)O(7) in an independent tetrahedron approximation in a finite field B along [111]. Such a model describes semi-quantitatively the collective paramagnetic regime where nontrivial spin correlations start to develop at the shortest length scale, that is over a single tetrahedron, but where no long range order is yet present. Our results show that a magnetization plateau develops at low temperatures as the system develops B = 0 ferromagnetic spin ice like 'two-in/two-out' correlations at the shortest length scale. From these results, we are led to propose that the observation of such a [111] magnetization plateau in Tb(2)Ti(2)O(7) would provide compelling evidence for a QSI at B = 0 in this material and help guide the development of a theory for the origin of its spin liquid state.
尽管居里 - 外斯温度θ(CW)约为 -14 K，但Tb(2)Ti(2)O(7)烧绿石磁性材料在至少低至T(*)≈50 mK时仍缺乏长程磁有序。最近有人提出，这种材料的低温集体顺磁或自旋液体状态可能类似于受热涨落和量子涨落影响的自旋冰态——某种量子自旋冰(QSI)。在此，我们探究沿[111]方向的磁场B对QSI态的影响。为此，我们在沿[111]方向的有限磁场B中，采用独立四面体近似研究Tb(2)Ti(2)O(7)微观模型的磁性。这样一个模型半定量地描述了集体顺磁区，在这个区域中，非平凡的自旋关联在最短长度尺度上开始发展，即在单个四面体上，但此时尚未出现长程有序。我们的结果表明，随着系统在最短长度尺度上发展出类似B = 0时铁磁自旋冰的“两进/两出”关联，低温下会出现磁化平台。基于这些结果，我们进而提出，在Tb(2)Ti(2)O(7)中观察到这样一个[111]磁化平台，将为该材料在B = 0时存在QSI提供有力证据，并有助于指导其自旋液体态起源理论的发展。
