Random Fields and the Partially-Paramagnetic State of CsCo₀.₈₃Mg₀.₁₇Br₃: A Critical Scattering Study

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Critical neutron scattering measurements have been performed on CsCo₀.₈₃Mg₀.₁₇Br₃, a dilute stacked triangular lattice (STL) Ising antiferromagnet (AF). A two component lineshape associated with the critical fluctuations appears at a temperature coincident with Tₙ₁ observed in pure CsCoBr₃. Such scattering is indicative of fluctuations in prototypical random field Ising model (RFIM) systems. The random field domain state arises in this case due to geometrical frustration within the STL Ising AF, which gives rise to a 3 sublattice Neel state, in which one sublattice is disordered. Magnetic vacancies nucleate AF domains in which the vacancies reside on the disordered sublattice thereby generating a RFIM state in the absence of an applied magnetic field.