First-order magnetic phase transitions

After the general properties of the first-order magnetic phase transitions between ordered structures were investigated, the number of possible models has been limited by supposing the sensitivity of the exchange energy to the interatomic distance to be responsible for the phase transition. It has shown that the magnetic phase transition occurs as a result of a sign-change in the proper combination of the exchange parameters. The transition may be influenced by the variation of the pressure and the magnetic field. The actual phase transition is, however, hindered in both directions by the elastic energy wall, separating the free energy minima of the different phases. The T – P phase diagram has been calculated and the conditions for the existence of a triple point in the T – P plane have been investigated in the case of antiferromagnetic ↔ ferromagnetic transitions. The temperature hysteresis, i.e. the difference between the upper (Tsup) and lower (Tinf) transition temperatures has been determined at different pressures and for both temperatures a linear dependence has been obtained. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3484

First-order magnetic phase transitions

After the general properties of the first-order magnetic phase transitions between ordered structures were investigated, the number of possible models has been limited by supposing the sensitivity of the exchange energy to the interatomic distance to be responsible for the phase transition. It has shown that the magnetic phase transition occurs as a result of a sign-change in the proper combination of the exchange parameters. The transition may be influenced by the variation of the pressure and the magnetic field. The actual phase transition is, however, hindered in both directions by the elastic energy wall, separating the free energy minima of the different phases. The T – P phase diagram has been calculated and the conditions for the existence of a triple point in the T – P plane have been investigated in the case of antiferromagnetic ↔ ferromagnetic transitions. The temperature hysteresis, i.e. the difference between the upper (Tsup) and lower (Tinf) transition temperatures has been determined at different pressures and for both temperatures a linear dependence has been obtained. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3484

Using Landau theory in first-order phase transitions

Landau theory can be applied to the transitions of the first or second order. For the case when the line of the first order phase transitions does not transform into the line of the second order phase transitions, i.e. not as ends with the tricritical point but not with a critical one: critical lines, limiting the region of metastable states, by using the Landau theory of phase transitions were determined

До питання про фазові переходи першого роду в ортоферитах

On the example of first-order phase transitions in orthoferrites under the influence of an external magnetic field is shown the effectiveness of the application of the Landau theory of phase transitions, commonly used in second-order phase transitions. This is especially important when used Hamiltonian is a function of many variables.На прикладі фазових переходів першого роду в ортоферитах під впливом зовнішнього магнітного поля показано результативність застосування теорії фазових переходів Ландау, що зазвичай використовуються при фазових переходах другого роду. Особливо це важливо, коли використовуваний гамільтоніан є функцією багатьох змінних