MAGNETOCALORIC EFFECT AND PRESSURE INFLUENCE ON DYSPROSIUM SINGLE-CRYSTAL MAGNETIZATION IN THE RANGE OF MAGNETIC PHASE-TRANSITION

Results of investigating the magnetocaloric effect and magnetic properties of dysprosium single crystals under the condition of atmospheric and high hydrostatic pressure of 10(10) dyn/cm2 are presented. A Dy magnetic phase diagram has been obtained. It is shown that in a tricritical point where two lines of the first type are converted into a line of a phase transition of the second type (helicoidal antiferromagnetism-fan structure) there are no volume jumps, entropy and magnetization. It has been discovered that in case of the helicoidal antiferromagnetic-ferromagnetic phase transition the volume magnetostriction jump will reach an enormous value of omeaga almost-equal-to (0.6-0.7) x 10(-3). A correlation between the temperature and field dependence of the volume magnetostriction and magnetocaloric effect has been revealed. It has been found out that the antiferromagnetic-ferromagnetic transition is caused by the fact that the free energy of an exchange interaction between magnetic layers in a ferromagnetic phase at decreasing temperature is less than the value of the same energy in an antiferromagnetic phase because of the magnetoelastic contribution to the energy of the exchange that increases greatly in case of temperature decrease.