M B Stone et al 2007 New J. Phys. 9 31 doi:10.1088/1367-2630/9/2/031
Field-driven phase transitions in a quasi-two-dimensional quantum antiferromagnet
Focus on Correlated Electrons, Magnetism and Superconductivity in High Magnetic FieldsM B Stone1,2,3,7, C Broholm2,4, D H Reich2, P Schiffer3, O Tchernyshyov2, P Vorderwisch5 and N Harrison6
Show affiliationsPart of Focus on Correlated Electrons, Magnetism and Superconductivity in High Magnetic Fields
We report magnetic susceptibility, specific heat, and neutron scattering measurements as a function of applied magnetic field and temperature to characterize the S = 1/2 quasi-two-dimensional (2D) frustrated magnet piperazinium hexachlorodicuprate (PHCC). The experiments reveal four distinct phases. At low temperatures and fields the material forms a quantum paramagnet with a 1 meV singlet triplet gap and a magnon bandwidth of 1.7 meV. The singlet state involves multiple spin pairs some of which have negative ground state bond energies. Increasing the field at low temperatures induces 3D long-range antiferromagnetic order at 7.5 Tesla through a continuous phase transition that can be described as magnon Bose–Einstein condensation. The phase transition to a fully polarized ferromagnetic state occurs at 37 Tesla. The ordered antiferromagnetic phase is surrounded by a renormalized classical region. The crossover to this phase from the quantum paramagnet is marked by a distinct anomaly in the magnetic susceptibility which coincides with closure of the finite temperature singlet–triplet pseudo gap. The phase boundary between the quantum paramagnet and the Bose–Einstein condensate features a finite temperature minimum at T = 0.2 K, which may be associated with coupling to nuclear spin or lattice degrees of freedom close to quantum criticality.
- PACS
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75.30.Kz Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
- Subjects
- Dates
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Issue 2 (February 2007)
Received 16 November 2006
Published 16 February 2007
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Field-driven phase transitions in a quasi-two-dimensional quantum antiferromagnet
M B Stone et al 2007 New J. Phys. 9 31
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