BiMnTeO 6 : A multiaxis Ising antiferromagnet
Résumé
The crystal and magnetic properties of honeycomb BiMnTeO6 have been studied between 1.5 and 300 K using synchrotron x-rays and neutron-scattering experiments. Commensurate magnetic ordering is observed below TN=10K, and corresponds to a noncollinear spin arrangement, with spins tilted away from the anisotropy easy-axis set by the Jahn-Teller distortion of the MnO6 octahedra. Inelastic-scattering experiments show two main nearly localized magnetic excitations, which can be well described by an exchange Hamiltonian involving weak Mn-Mn magnetic interactions and a crystal-field Hamiltonian characterizing the strong easy-axis anisotropy associated with the dz2 orbital ordering of Mn3+. The crystal-field levels can be accurately calculated, taking into account a transverse molecular field imposed by the magnetic ordering of the neighboring atoms below TN. This makes BiMnTeO6 an interesting example of a multiaxis Ising system in a self-imposed transverse magnetic field.
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