Stabilization of Néel order in frustrated magnets with increasing magnetic ﬁeld
Max-Planck-Institut für Chemische Physik fester Stoﬀe, Dresden, Germany
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For low-dimensional frustrated quantum magnets, the dependence of the staggered moment ms on a magnetic ﬁeld is nonmonotonic: For small and intermediate ﬁelds, quantum ﬂuctuations are gradually suppressed, leading to an increase of ms (H). For large applied magnetic ﬁelds however, the classically expected monotonous decrease is recovered. For the same reasons, the Néel ordering temperature TN of such compounds ﬁrst increases and then exhibits a reentrant behavior as a function of the ﬁeld strength. The quantitative analysis of this behavior is an excellent tool to determine the frustration parameter of a given compound. We have derived a general linear spin-wave (LSW) theory in the presence of a magnetic ﬁeld. Based on our LSW theory, including a small interlayer coupling, we use a self-consistent approach determining TN by the condition of a vanishing total moment. We apply our ﬁndings to the recently measured ﬁeld dependence of the magnetic ordering temperature TN of Cu(pz)2 (ClO4)2 in the framework of the S = 1/2 two-dimensional J1-J2 Heisenberg model. The observed increase with increasing ﬁeld strength can be understood naturally using an intermediate frustration ratio J2/J1 ≈ 0.2, which is in accordance with the ﬁeld dependence of the staggered moment.
© Owned by the authors, published by EDP Sciences, 2013