ac susceptibility study of the d=3 random-field critical dynamics

Magnetic and structural properties of the solid solution CuAl2(1-x)Ga2xO4

CuAl₂O₄ is a ternary oxide spinel with Cu²⁺ ions ([Formula: see text]) primarily populating the A-site diamond sublattice. The compound is reported to display evidence of spin glass behavior but possess a non-frozen magnetic ground state below the transition temperature. On the other hand, the spinel CuGa₂O₄ displays spin glass behavior at ~ 2.5 K with Cu²⁺ ions more readily tending to the B-site pyrochlore sublattice. Therefore, we investigate the magnetic and structural properties of the solid solution CuAl_2(1-x)Ga_2xO₄ examining the evolution of the magnetic behavior as Al³⁺ is replaced with a much larger Ga³⁺ ion. Our results show that the Cu²⁺ ions tend to migrate from tetrahedral to octahedral sites as the Ga³⁺ ion concentration increases, resulting in a concomitant change in the glassy magnetic properties of the solution. Results indicate glassy behavior for much of the solution with a general trend towards decreasing magnetic frustration as the Cu²⁺ ion shifts to the B-site. However, the [Formula: see text] and 0.2 members of the system do not show glassy behavior down to our measurement limit (1.9 K) suggesting a delayed spin glass transition. We suggest that these two members are additional candidates for investigation to access highly frustrated exotic quantum states.

Order parameter criticality of the d = 3 random-field Ising antiferromagnet Fe0.85Zn0.15F2

The critical exponent beta=0.16+/-0.02 for the random-field Ising model order parameter is determined using extinction-free magnetic x-ray scattering for Fe0.85Zn0.15F2 in magnetic fields of 10 and 11 T. The observed value is consistent with other experimental random-field critical exponents, but disagrees sharply with Monte Carlo and exact ground state calculations on finite-sized systems.