Main field of study:  010700 Physics
Area of specialisation: : Quantum Mechanics of Atoms, Molecules and Solids 
Scientific advisor: Prof. A.I. Sokolov
Reviewer: Doc. A.O.Sorokin  
 
The role of magnetic dipole-dipole interaction in helical magnets
V.E. Timofeev 

Recently fundamental researches of multiferroic compounds have gained special interest among scientists. One of such compounds is helical magnet manganese(ii) iodide that contains a cascade of three magnetic phase transitions. Explanation of the nature of these phase transitions is urgent theoretical task nowadays.
In this research paper an energy model of manganese(ii) iodide is developed. The model contains magnetic dipole-dipole interaction that describes the ground state of the system: the incommensurate modulation vector and unusual position of the plane of polarization of the spins normal to the modulation vector.
Free energy has been considered in the approximation of the mean-field theory. Phase transition temperatures were calculated. The phase diagram that describes the cascade of phase transitions observed in the experiment has been constructed.