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In this report, we present results of the direct measurements of the adiabatic temperature change in MnAs1−xPx compounds (x = 0, 0.02, 0.025, and 0.03) in cyclic magnetic fields up to 8 T. The substitution of As by P results in a slight shift of the Curie temperature and more notable change in the magnetocaloric effect (MCE) value. Estimations of the lattice and magnetic contributions show that in the MnAs compound, the lattice contribution dominates (about 70% of the total MCE). Substitution of As with phosphorus leads to a decrease in the total value of the MCE, which is caused by a decrease in the lattice contribution, and the magnetic contribution almost does not change in the absolute value. A reversible degradation of the magnetocaloric effect in cyclic magnetic fields is found, which restricts the application of this material to the magnetic cooling technology.

The phase transitions and critical phenomena of the three-dimensional antiferromagnetic Heisenberg model on a body-centered cubic lattice with next and next-nearest neighbor interactions are studied using the replica Monte Carlo algorithm. Investigations are carried out for relations of exchange interaction values of next and next-nearest neighbors in the range of k values [0.0, 0.6]. A behavior of phase transitions is analyzed by the histogram method. A whole set of main static critical exponents is estimated within the finite-size scaling theory. The universality class of the model critical behavior is shown to be unchanged in the considered interval of k value.

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