Guruciaga P C, Pili L, Boyeras S, Slobinsky D, Grigera S A, Borzi R A
Centro Atómico Bariloche, Comisión Nacional de Energía Atómica (CNEA), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Av. E. Bustillo 9500, R8402AGP San Carlos de Bariloche, Río Negro, Argentina.
Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB), UNLP-CONICET, B1900BTE La Plata, Argentina.
J Phys Condens Matter. 2020 Jul 27;32(42). doi: 10.1088/1361-648X/aba153.
We study experimentally and numerically the dynamics of the spin ice material DyTiOin the low temperature () and moderate magnetic field () regime (∈ [0.1, 1.7] K,∈ [0, 0.3] T). Our objective is to understand the main physics shaping the out-of-equilibrium magnetisation vs temperature curves in two different regimes. Very far from equilibrium, turning on the magnetic field after having cooled the system in zero field (ZFC) can increase the concentration of magnetic monopoles (localised thermal excitations present in these systems); this accelerates the dynamics. Similarly to electrolytes, this occurs through dissociation of bound monopole pairs. However, for spin ices the polarisation of the vacuum out of which the monopole pairs are created is a key factor shaping the magnetisation curves, with no analog. We observe a threshold field near 0.2 T for this fast dynamics to take place, linked to the maximum magnetic force between the attracting pairs. Surprisingly, within a regime of low temperatures and moderate fields, an extended Ohm's law can be used to describe the ZFC magnetisation curve obtained with the dipolar spin-ice model. However, in real samples the acceleration of the dynamics appears even sharper than in simulations, possibly due to the presence of avalanches. On the other hand, the effect of the field nearer equilibrium can be just the opposite to that at very low temperatures. Single crystals, as noted before for powders, abandon equilibrium at a blocking temperaturewhich increases with field. Curiously, this behaviour is present in numerical simulations even within the nearest-neighbours interactions model. Simulations and experiments show that the increasing trend inis stronger for‖[100]. This suggests that the field plays a part in the dynamical arrest through monopole suppression, which is quite manifest for this field orientation.
我们通过实验和数值方法研究了自旋冰材料DyTiO在低温（(T\in [0.1, 1.7], K)）和中等磁场（(H\in [0, 0.3], T)）条件下的动力学特性。我们的目标是理解在两种不同条件下塑造非平衡磁化强度与温度曲线的主要物理机制。在远离平衡态时，先在零磁场（ZFC）下冷却系统后再开启磁场，会增加磁单极子的浓度（这些系统中存在的局域热激发）；这会加速动力学过程。与电解质类似，这是通过束缚磁单极子对的解离发生的。然而，对于自旋冰来说，产生磁单极子对的真空极化是塑造磁化曲线的一个关键因素，没有类似情况。我们观察到对于这种快速动力学过程发生有一个接近0.2 T的阈值场，这与吸引对之间的最大磁力有关。令人惊讶的是，在低温和中等磁场条件下，可以用扩展的欧姆定律来描述用偶极自旋冰模型得到的ZFC磁化曲线。然而，在实际样品中，动力学的加速似乎比模拟中更明显，可能是由于雪崩的存在。另一方面，接近平衡态时磁场的影响可能与极低温度时的影响相反。如之前对粉末所指出的，单晶在一个随磁场增加的阻塞温度下偏离平衡态。奇怪的是，即使在最近邻相互作用模型中，这种行为在数值模拟中也存在。模拟和实验表明，对于(H\parallel[100])，(T_B)的增加趋势更强。这表明磁场通过磁单极子抑制在动力学阻滞中起作用，对于这个磁场方向来说这一点相当明显。
