CuMoO4 is a triclinic quantum magnet based on S=1/2 moments at the Cu2+ site. It has recently attracted interest due to the remarkable changes in its chromic and volumetric properties at high temperatures and in its magnetic properties at low temperatures. This material exhibits a first-order structural phase transition at TC ∼ 190 K as well as a magnetic phase transition at TN ∼ 1.75 K. We report low-temperature heat capacity measurements as well as extensive elastic and inelastic neutron scattering measurements on powder samples taken above and below TN. We observe neutron diffraction consistent with a simple (1/2, 0, 0) antiferromagnetic structure indicating a doubling of the a-axis periodicity below TN. In addition, inelastic neutron scattering above a spin gap of ∼2.3 meV is consistent with triplet excitations out of paired S=1/2 moments which form singlet dimers. Low-lying spin wave excitations are also observed and these originate from ordered S=1/2 moments below T N. Taken together these measurements show the ground state of CuMoO4 to display both nonmagnetic singlets and ferromagnetically coupled spins coexisting within an antiferromagnetic structure below T N ∼ 1.75 K.
|ジャーナル||Physical Review B - Condensed Matter and Materials Physics|
|出版ステータス||出版済み - 9月 22 2011|
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