Unquenched Geometric Frustration Effect on Spiral Spin Correlation in Magnetically Ordered Phase

抄録

We studied magnetic phase diagram and x-dependence of spiral spin correlation in magnetically ordered phase of (Co_1−xZn_x)Cr₂O₄ by magnetization and neutron scattering experiments. The spiral correlation survives in a wide x range from 0 to 0.9. As x increases, the correlation length decreases from ξ∼23 Å at x=0, and saturates at ξ∼2.5 Å at around x=0.75, which is close to the nearest neighboring Cr³⁺-Cr³⁺ distance. The pitch is almost constant from x=0 to 0.75, then abruptly shortens above around x=0.75. The correlation is isotropic at x=0.25 but anisotropic at x=0.75. We discuss that the spiral correlation is of short-range owing to unquenched geometric frustration, and begins to collapse with the minimization of correlation length above around x=0.75, possibly as the precursor of dynamic spin hexamer caused by high geometric frustration.