Nonlinear susceptibilities as a probe to unambiguously distinguish between canonical and cluster spin glasses

Abstract

Treating the randomly Fe-substituted optimally hole-doped manganite La0.7Pb0.3(Mn1−yFey)O3 (y=0.2,0.3) as a test case, we demonstrate that a combined investigation of both odd and even harmonics of the ac magnetic response permits an unambiguous distinction between the canonical and cluster spin glasses. As expected for a spin glass (SG), the nonlinear ac magnetic susceptibilities χ3(T,ω) and χ5(T,ω) (odd armonics) diverge at the SG freezing temperature Tg=80.00(3) K [Tg=56.25(5) K] in the static limit and, like the imaginary part of the linear susceptibility, follow dynamic scaling with the critical exponents β=0.56(3) [β=0.63(3)], γ=1.80(5) [γ=2.0(1)], and zν=10.1(1) [zν=8.0(5)] in the sample with composition y=0.2 (y=0.3). The nonlinear susceptibility χNL, which has contributions from both χ3 and χ5, satisfies static scaling with the same choice of Tg, β, and γ. Irrespective of the Fe concentration, the values of the critical exponents γ, ν, and η are in much better agreement with those theoretically predicted for a three-dimensional (d=3) Heisenberg chiral SG than for a d=3 Ising SG. The true thermodynamic nature of the “zero-field” spin-glass transition is preserved even in finite magnetic fields. Unlike odd harmonics, even harmonics χ2(T,ω) and χ4(T,ω) make it evident that, apart from the macroscopic length scale of the spin-glass order in the static limit, there exists a length scale that corresponds to the short-range ferromagnetic order.