## Abstract

Quantum antiferromagnet NH_{4}CuCl_{3} shows magnetization plateaus at 1/4 and 3/4 of the saturation magnetization. Specific heat measurements at ambient pressure and magnetization measurements under hydrostatic pressure were performed on NH_{4}CuCl_{3} in magnetic fields. From specific heat measurements, we obtained the detailed magnetic phase diagram below 9 T, which includes the lower edge field H _{c1} of 1/4 plateau. The phase boundary just below H_{c1} can be described by a power low, H_{c1} - H_{N}(T) ∝ T ^{φ} with φ = 2, where H_{N}(T) is the transition field at temperature T. Magnetic susceptibility measurements under pressure revealed reentrant quantum phase transitions, such that the gapless ground state at zero field changes into gapped state with increasing pressure, and further into gapless state again.

Original language | English |
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Pages (from-to) | 241-245 |

Number of pages | 5 |

Journal | Progress of Theoretical Physics Supplement |

Volume | 159 |

DOIs | |

Publication status | Published - 2005 |

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