The novel field-induced re-entrant phase in multiferroic hexagonal HoMnO3 is investigated to lower temperatures by dc magnetization, ac susceptibility, and specific heat measurements at various magnetic fields. Two new phases have been unambiguously identified below the Neel transition temperature, TN=76 K, for magnetic fields up to 50 kOe. The existence of an intermediate phase between the P[6]_3[c]m and P[6]_3c[m] magnetic structures (previously predicted from dielectric measurements) was confirmed and the magnetic properties of this phase have been investigated. At low temperatures (T<5 K) a dome shaped phase boundary characterized by a magnetization jump and a narrow heat capacity peak was detected between the magnetic fields of 5 kOe and 18 kOe. The transition across this phase boundary is of first order and the magnetization and entropy jumps obey the magnetic analogue of the Clausius-Clapeyron relation. Four of the five low-temperature phases coexist at a tetracritical point at 2 K and 18 kOe. The complex magnetic phase diagram so derived provides an informative basis for unraveling the underlying driving forces for the occurrence of the various phases and the coupling between the different orders.
Field-induced ferroelectric and commensurate spin state in mutiferroic HoMn$_{2}$O$_{5}$
对多铁性化合物HoMn $_{2}$ O $_{5}$进行了强磁场下的中子衍射测量。在零磁场下，高温无公度磁（HT-ICM）-公度磁（CM）-低温无公度磁（LT-ICM）顺序随温度的降低而发生，其中铁电极化仅出现在CM相。在施加磁场时，LT-ICM相完全消失，并且在最低温度下诱导CM相。这种场致CM状态与这种材料中的场致电极化的强度完全相关[Higashiyama { \it et al}.，Phys. Rev. B { \bf 72}，064421（2005）.]，强有力地表明，在多铁性$R$ Mn $_{2}$ O $_{5}$系统中，公度自旋态是铁电性的必要条件。
Temperature induced phase transition from cycloidal to collinear antiferromagnetism in multiferroic Bi$_{0.9}$Sm$_{0.1}$FeO$_3$ driven by $f$-$d$ induced magnetic anisotropy
Temperature-induced gap formation in dynamic correlation functions of the one-dimensional Kondo insulator --- Finite-temperature density-matrix renormalization-group study ---
Finite temperature fluctuation-induced order and responses in magnetic topological insulators
我们推导出磁性拓扑绝缘体的有效场论模型，并预测，磁电子间隙持续的表面上的温度高于订购温度的散装。我们的分析也适用于由铁磁和拓扑绝缘体组成的异质结构的界面。为了对MnBi $_2$ Te $_4$和EuS-Bi $_2$ Se $_3$异质结构进行定量预测，我们将有效场论方法与密度泛函理论和蒙特卡罗模拟相结合.对于MnBi $_2$ Te $_4$，我们预测在表面上向上的Néel温度偏移高达$15 \%$，而EuS-Bi $_2$ Se $_3$界面表现出较小的相对偏移。有效理论还预测了诱导Dzyaloshinskiii-Moriya相互作用和拓扑磁电效应，这两者都具有有限的温度和化学势依赖性。
