Strain-induced magnetic moment enhancement in frustrated antiferromagnet Cs₂CuBr₄

The structure and magnetic properties are studied in co-doped Cs_2−xK_xCuBr_4−xCl_x and pressurized Cs₂CuBr₄ samples. No structural phase transition is found with doping concentration x ⩽ 0.1 and pre-compression pressure up to 4.5 GPa. The maximum susceptibility temperature T _max of the zero-field-cooling (ZFC) susceptibility curves decreases slightly with increasing doping concentration and pre-compression pressure, indicating only small changes in the exchange coupling constants. However, an unusual enhancement of the magnetic moment deduced from the ZFC susceptibility is observed in both series samples. A maximum increase of 40% is obtained in Cs_1.9K_0.1CuBr_3.9Cl_0.1 sample. The magnetic moment increases almost linearly with decreasing Δ, i.e., defined as the wavenumber difference between the short- and long-bond stretching modes of the CuBr₄ ²⁻ tetrahedra in the Raman spectra. The effect is likely due to the recovery of the Cu-3d orbital magnetic moments by strain-induced suppression of Jahn–Teller distortion in CuBr₄ ²⁻ tetrahedra. (paper)