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Abstract: Anisotropic antiferromagnets in an external magnetic field show a richvariety of different ground states meeting in transition lines andmulticritical points. We study the dependence of the ground states of thesesystems in the three dimensional space on physical parameters as exchange,single ion and cubic anisotropy.One identifies four different ground states: the paramagnetic PM, theantiferromagnetic AF, the spin flop SF and the biconical BC ground state.In the case of absence of a cubic anisotropy the transition lines separatingthe different ground states can be calculated analytically, otherwise they haveto be calculated numerically. We also considered the behavior of the staggeredmagnetization which characterizes the different ground states. From itsbehavior the order of the transition from one state to the other is determined.But also the order of the transition changes along the transition lines whenincluding the cubic anisotropy, especially at the reeentrant region where atransition from SF to BC and back to SF by increasing the external field $H$occurs. Multicritical points are founded which are assumed to be tricritical orcritical endpoints. The results obtained may be relevant for other systemssince the antiferromagnetic model can be mapped to a lattice gas model wherethe biconical ground state is interpreted as supersolid phase. Recentrenormalization group calculations show that such a phase would indicate theexistence of a tetracritical point.



Author: T.-C. Dinh, R. Folk

Source: https://arxiv.org/







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