Calculation of the H–T phase diagram, magnetization and susceptibility in layered structures

The magnetic field–temperature (H–T) phase diagram is calculated using the mean field theory by expanding the free energy in terms of the uniform and staggered magnetization for the ferromagnetic–antiferromagnetic transitions in the La_0.6Nd_0.4Mn₂Si₂ multilayer structures. Using our experimental measurements, analysis of the magnetization as a function of the magnetic field at constant temperatures from 45 K to 250 K is performed by a power-law formula close to the ferromagnetic–antiferromagnetic transitions. Also, by obtaining the magnetic field dependence of the isothermal susceptibility χ_T from the M–H curves, χ_T vs. H−H_c is analyzed (H_c is the critical magnetic field) using a power-law formula for the antiferromagnetic–ferromagnetic (AF–FM) transitions in La_0.6Nd_0.4Mn₂Si₂. It is found that a discontinuous (first order) transition which occurs at the lowest (45 K) and the highest (250 K) temperatures, changes to a continuous one at a constant temperature at around 100 K as the magnetic field carries the systems from the antiferromagnetic to the ferromagnetic phase. Values of the critical exponents associated with this transition are deduced and they are compared with the predictions of some theoretical models. - Highlights: • H–T phase diagram is calculated for rare-earth silicide layered structures. • Mean field theory is used for calculation of the phase diagram in La_0.6Nd_0.4Mn₂Si₂. • Magnetization and susceptibility are analyzed using the experimental data. • The critical exponents deduced are interpreted for the AF–FM transition. • Weak first order is indicated for the AF–FM transition in La_0.6Nd_0.4Mn₂Si₂