Superspin glass behavior and giant exchange bias effect in hexagonal (Mn0.7Cu0.3)66Ga34 ferrimagnet

A hexagonal Ni₂In-type single phase is obtained in the (Mn_0.7Cu_0.3)₆₆Ga₃₄ sample. The superspin glass (SSG) behavior and exchange bias effect are investigated in depth. The DC thermomagnetic M(T) measurements show a remarkable bifurcation between the zero-field cooling and field-cooling patterns below 100 K, suggesting a SSG behavior, which is verified by the simulation of de Almeida–Thouless relation from M(T) curves under different fields. Furthermore, the SSG behavior is justified by the AC susceptibility, temporal magnetic relaxation, and memory effect measurements. The asymmetric response of memory effect clearly indicates that it supports the hierarchical model. More importantly, the fitted parameters including Mydosh parameter Φ = 0.0255, dynamical critical exponent zv = 10.02, and τ₀ ~ 5.5 × 10⁻⁹ s give the convincing evidences for the SSG behavior at low temperatures for (Mn_0.7Cu_0.3)₆₆Ga₃₄. Above all, a giant exchange bias field of μ₀H_EB = 308.4 mT is obtained at T = 2 K under the cooling field μ₀H_CF = 0.5 T and maximum applied magnetic field |μ₀H_max| = | +μ₀H | = | −μ₀H | = 8 T. The origin for giant exchange bias effect is discussed.