Abstract
Ferrimagnets in which half the spins are disordered and half ordered, so-called half-fire, half-ice state, have been advanced theoretically as a route towards realizing exotic magnetic ground states. Here we demonstrate novel single-spin resonance in SmMn₂Ge₂, a 1/3-fire, 2/3-ice material. Using ac-susceptibility in the frequency range 0.1 Hz - 1 kHz we find a Debye-like resonance with Orbach relaxation temperature dependence, yielding an energy barrier E_B ≈ 840 k_B and attempt frequencies in the THz range. These quantities strongly suggest single-spin relaxation among paramagnetic Sm spins where the flipping field is provided by the FM-ordered Mn spins at domain boundaries, a direct outcome of the 1/3-fire, 2/3-ice state.