Divergent effects of static disorder and hole doping in geometrically frustrated β-CaCr₂O₄

The gallium substituted and calcium deficient variants of geometrically frustrated β-CaCr₂O₄, β-CaCr _22xGa_2xO₄ (0.02≤x≤0.25) and β-Ca_1-yCr₂O₄ (0.075≤y≤0.15), have been investigated by X-ray powder diffraction, magnetization and specific heat measurements. This allows for a direct comparison of the effects, in a geometrically frustrated magnet, of the static disorder that arises from non-magnetic substitution and the dynamic disorder that arises from hole doping. In both cases, disturbing the Cr³ lattice results in a reduction in the degree of magnetic frustration. On substitution of Ga, which introduces disorder without creating holes, a gradual release of spins from ordered antiferromagnetic states is observed. In contrast, in the calcium-deficient compounds the introduction of holes induces static ferrimagnetic ordering and much stronger perturbations of the β-CaCr₂O₄ host.