Localized magnetism, magnetic entropy change and critical properties of Mn[formula omitted]NbS2 single crystals

Abstract

Magnetic properties, magnetic entropy change and critical behavior of Mn1/4+δNbS2 single crystals have been investigated by easy axial magnetization measurements. The magnetization as a function of temperature (T) under fixed magnetic field H = 1 kOe M (T, 1 kOe) shows two magnetic phase transitions at around 45 K and 105 K, respectively, suggesting the intertwining of Mn1/3NbS2 and Mn1/4NbS2. At paramagnetic state, M (T, 1 kOe) is well captured by the Curie–Weiss law and the effective magnetic moment is deduced to be 5.9 ±0.2μB/Mn, corresponding to a localized Mn2+ ion with S = 52. At T = 2 K, the magnetization saturates quickly around 200 Oe and the spontaneous magnetic moment is estimated to be 5.0(1)μB/Mn. The derived effective and saturation moment indicate that the spin moment of the intercalants are hardly affected by the hosts. In accordance with the two magnetic phase transitions, magnetic entropy change ΔSM shows two series of peaks. At ΔH=7 T, the maxima of ΔSM reach 2.2(8) and 2.6(2) J kg−1 K−1 at 45 K and 105 K, respectively. Analysis of the critical exponents gives β = 0.3593(1), γ = 1.1483(3) and δ = 3.968(3). Although the deduced exponents can fulfill the scaling equations, it is found that they cannot be categorized into a single theoretical model, implying competing magnetic couplings in this crystal.