The magnetic Field-temperature (H-T) phase diagram is calculated using the mean held theory by expanding the free energy in terms of the uniform and staggered magnetization for the ferromagnetic-antiferromagnetic transitions in the La0.6Nd0.4Mn2Si2 multilayer structures. Using our experimental measurements, analysis of the magnetization as a function of the magnetic held 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 chi(T) from the M-H curves, chi(T) vs. H-H-c, is analyzed (H-c is the critical magnetic field) using a powerlaw formula for the antiferromagnetic-ferromagnetic (AF-FM) transitions in La0.6Nd0.4Mn2Si2. 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. (C) 2015 Elsevier B.V. All rights reserved.