Figure 5
From: Unveiling the Physics of the Mutual Interactions in Paramagnets
Average magnetic energy and external magnetic field dependence of the entropy. Upper panel: Entropy S as a function of the average magnetic energy E for B = 1, 2 T; Bloc = 0 T and \(N=(6.022\times {10}^{23})\). The horizontal black arrow indicates the possibility of changing the sign of the magnetic energy when the direction of the external magnetic field (red arrow) is varied in the time scale of μs resulting predominantly in an anti-parallel configuration of the magnetic moment in respect to \(\overrightarrow{\mu }\) (blue arrow), as proposed in the Purcell and Pound’s experiment50. The colorful background indicates that negative (red) temperatures are hotter than positive (blue) ones. Lower panel: Entropy S as a function of the external magnetic field B for the Brillouin model at T = 5 and 1 mK considering Bloc = 0 T and Bloc = 0.01 T, cf. label. The dashed lines in both panels represent the entropy saturation \(S={k}_{B}\,\mathrm{ln}\)(2), i.e., the entropy value for \(({\mu }_{B}B/{k}_{B}T)\to 0\). The colorful background depicts the insensitivity of \({(\partial S/\partial B)}_{T}\) regarding positive or negative temperatures, cf. discussed in the main text. Figure created with use of OriginPro (version 2020)63 and Wolfram Mathematica (version 11)64.
