Peculiarities of Magnetocaloric Effect in Ferromagnetic Cylindrical Nanowires with a Domain Wall

It is established that in a weak magnetic field significantly lower than 2М, where M is the magnetization of a ferromagnetic cylindrical nanowire, the entropy of the latter increases due to the thermal motion of the domain wall comprised in it. As a result, a negative magnetocaloric effect emerges in this system. This phenomenon has a nanoscale nature and disappears with moving to bulk materials. It is shown that the established effect is in accordance with the fundamental Le Chatelier-Brown principle for the selfregulating thermodynamic systems. The obtained result is of significant interest in the context of the development of new methods to achieve precise temperature values on the low dimensional magnetic nanostructures. In turn, in strong magnetic fields of the order of the magnetic field generated by the movement of electrons in atoms (~ (1-10) kOe) a positive magnetocaloric effect takes place, i.e. the temperature of the ferromagnetic nanowire increases with increasing amplitude of the magnetic field. For the diameter of the nanowire, an estimate is given at which the transition from the longitudinal domain wall to the domain wall in the form of a Bloch point occurs.