Temperature Dependence of ⁵⁵Mn NMR Frequency on Various Environments in Dilute NiMn Alloys

Abstract

The temperature dependence of ⁵⁵Mn NMR frequency has been studied in dilute NiMn alloy from 4.2 to 520 K by the spin echo method. The ⁵⁵Mn NMR signal associated with the parallel moment to the host consists of three parts: Mn⁰, Mn¹ and Mn² atoms that have 0, 1 and 2 Mn atoms in their nearest neighbours, respectively. The temperature dependence of respective NMR frequencies ν(T) is described by a common function Δν(T)⁄ν(0)=0.58×(T⁄T_Ci)^2.39, which indicates that each moment behaves as if it has different Curie temperature T_Ci depending on the different environment irrespectively of the Mn concentration in dilute Mn system. T_Ci’s of Mn⁰ and Mn¹ atoms are determined as 610 and 570 K, respectively. ν(T) of ⁵⁵Mn in FeMn_1.5% and CoMn_3% alloys are also described by this function, where T_Ci of Mn⁰ atoms in FeMn_1.5% and CoMn_3% alloys are 505 and 525 K, respectively. The ratios of the effective exchange interaction parameters are inferred directly from these values of T_Ci.