Low-energy magnetic excitations in the mixed spin-( 1 2 , 5 2 ) chain

We present studies on the low-energy magnetic excitations in the Lieb-Mattis (LM) ferrimagnetic phase. We investigate the low-energy magnetic excitations in the mixed spin-(12,52) chain (4−Br−o−MePy−V)FeCl4 based on low-temperature specific heat and multifrequency electron spin resonance (ESR) measurements. A clear T term is observed in the specific heat, which indicates a contribution of the low-energy magnetic excitation with a ferromagnetic quadratic dispersion expected in the LM ferrimagnetic state. Through the ESR mode analysis, we examine the effects of magnetic anisotropy on the excited states in the LM plateau phase.