Nonmonotonic Field Dependence Of The Neel Temperature In The Quasi-Two-Dimensional Magnet [Cu(Hf2)(Pyz)(2)]Bf4
The measured thermodynamic phase diagram of the quasi-two-dimensional magnet [Cu(HF2)(pyz)(2)]BF4(pyz=pyrazine=N2C4H4) exhibits an unusual nonmonotonic dependence of the Neel temperature T-N as a function of magnetic field H. The nonmonotonic behavior of T-N(H) results from two competing effects induced by the field: while H suppresses the amplitude of the order parameter by polarizing the spins along a given direction, it also reduces the phase fluctuations by changing the order parameter space from the sphere S-2 to the circle S-1. The latter effect dominates at low fields only if the system is close enough to its lower critical dimension (d(c)=2), i.e., when fluctuations become important. Our theoretical results reproduce the measured phase diagram and demonstrate that this unusual effect is realized in [Cu(HF2)(pyz)(2)]BF4.
Original Publication Title
Physical Review B
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Sengupta, P; Batista, C D.; McDonald, R D.; Cox, S; Singleton, J; Huang, L; Papageorgiou, T P.; Ignatchik, O; Herrmannsdorfer, T; Manson, Jamie L.; Schlueter, J A.; Funk, K A.; and Wosnitza, J, "Nonmonotonic Field Dependence Of The Neel Temperature In The Quasi-Two-Dimensional Magnet [Cu(Hf2)(Pyz)(2)]Bf4" (2009). Chemistry and Biochemistry Faculty Publications. 19.