47 research outputs found
Co-existing Singlet and Ordered S=1/2 Moments in the Ground State of the Triclinic Quantum Magnet CuMoO4
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 T_C ~ 190 K as well as a magnetic phase transition at T_N ~
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 T_N. We observe neutron diffraction consistent
with a simple (1/2, 0, 0) antiferromagnetic structure indicating a doubling of
the a-axis periodicity below T_N. 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 non-magnetic singlets, and ferromagnetically-coupled spins
coexisting within an antiferromagnetic structure below T_N ~ 1.75 K.Comment: 7 pages, 7 figure