ABSTRACT
Magnetothermal and magnetocaloric properties were investigated in various oxide compounds: garnets, orthoaluminates, vanadites,manganites and ferrites. Rare earth iron garnets (R3Fe5O12Þ and various ferrites can have several different magnetic sublattices with antiferromagnetic or more complex noncollinear ordering and exhibit various magnetic transitions and transformations typical for ferrimagnets, in particular such as compensation points. The transformations of their magnetic structure by temperature and magnetic field should be reflected on magnetocaloric properties. Gallium and aluminium rare earth garnets (R3Ga5O12 and R3Al5O12Þ are characterized by low magnetic ordering temperatures (usually several K) and are paramagnetic in the rest of the temperature interval. Analogous behaviour displays orthoaluminates (RAlO3Þ and vanadites (RVO4Þ. Due to the presence of rare earth ions the abovementioned oxide compounds can have an essential magnetic entropy change. The orthoaluminates and vanadites also have a higher percentage content of RE ion per mole in comparison with garnets, which can provide higher specific MCE per mole and cm3-an important parameter for practical applications. Perovskite-type manganites (RMnO3Þ with various dopants and related compounds attract the attention of investigators because of their interesting and complex magnetic and electrical properties, such as colossal magnetoresistance effect, charge and orbital ordering and electronic phase separation. Such compounds can reveal first-order magnetic phase transitions with a sharp change of magnetization and, because of that, high magnetocaloric properties. This circumstance, together with the ability to change in wide range the magnetic phase transition temperatures by variation of their composition (Curie temperatures of some compositions lie in room temperature range), makes the manganites attractive for applications in magnetic refrigerators.
