High-field ESR in a two-dimensional S=1 spin system Ni5(TeO3)4Br2

Abstract Single crystals of a transition-metal tellurium oxy-bromide Ni 5 (TeO 3 ) 4 Br 2 with a layered arrangement of Ni 2+ ( S =1) ions have been investigated with a high-frequency electron spin resonance (ESR). Strongly temperature-dependent resonance signal has been found only at temperatures lower than T c 2 =15 K. The measured signal exhibits a dramatic narrowing and a complex temperature dependence of the resonance center on cooling. The magnetic resonance results also indicate a zero-field gap ω g =450 GHz. The results are discussed in connection with the structural and magnetic susceptibility data.