Single Crystal Growth And Magnetic Phase Transition Of Rare-Earth Perovskites PrFe_1-xMn_xO₃

The rare earth orthoferrites RFe O₃?R=Rare earth or Y?belong to a distorted orthorhombic structure with a space group of Pbnm.As one of the functional materials,the potential applications of rare earth orthoferrites in magnetic switches,sensors,and magnetic storages have attracted the attention of many researchers in the world.In RFe O₃ systems,there are two sets of magnetic lattices of rare earth ions R³⁺and ironextremely complex magnetic properties and abundantly phase transitions,such as spin reorientation transitions,and spin switching.This thesis takes the rare earth orthoferrite PrFe O₃ as the research object,systematically studies the magnetic anisotropy of PrFe O₃single crystal at low temperature.In addition,we investigated the effects of changes in Mn³⁺doping concentration on the crystal structure and magnetic phase transition of PrFe_1-xMn_xO₃ series samples.1)Polycrystalline samples of PrFe_0.5Mn_0.5O₃,PrFe_0.25Mn_0.75O₃,and Pr Mn O₃ were prepared by the solid-state reaction method.Powder X-ray diffraction determined the samples are pure with a single-phase orthorhombic perovskite structure.Large-size PrFe O₃ single crystal and doped series PrFe_0.75Mn_0.25O₃ single crystal were grown by the optical floating zone method.Scanning electron microscopy?SEM?and composition analysis?EDS?showed that the ratio of each element of the growing single crystal was consistent with the nominal ratio,and the surface of the single crystal was smooth.Using Laue back-reflection diffractometer to determine the crystal axis of single crystals and a directional cutting was performed using a diamond precision cutting machine for subsequent magnetic measurements.2)Under very small applied magnetic field,the spin reorientation transition of?₄?Gx,Ay,Fz?-?₂?Fx,Cy,Gz?was observed in the PrFe O₃ single crystal,and suppressed in large magnetic fields.In the c-axis of PrFe O₃single crystal,we found the spin switching at the field-cooled-cooling processes,and we also found the reverse spin switching during field-cooled-warming regime.These spin switching effects are result from the change of the parallel/anti-parallel coupling of magnetic moments of Pr³⁺and Fe³⁺,and regulated by the magnetic fields.3)The structure refinement of PrFe_1-xMn_xO₃series polycrystalline samples shows that the sublattice distortion of the system increase with the increase of doping Mn³⁺.After doping with Mn³⁺,there is a competition between ferromagnetic and antiferromagnetic in the system,and an interesting negative magnetization phenomenon appears in the PrFe_0.25Mn_0.75O₃ polycrystal.It is worth mentioning that when the doping concentration of Mn³⁺x?0.5,the spin reorientation transition disappears in the system.4)The magnetic measurements of Mn doped PrFe O₃ shows that the spin reorientation transition of PrFe_0.75Mn_0.25O₃ single crystal change from?₄-?₂ to?₄-?₁,and the temperature of the transition also increases from 6.5 K-10 K to 295 K-297 K near the room temperature.The doping of Mn³⁺has an important effect on the coupling of the Pr³⁺and Fe³⁺,and achieves dual control of the phase transition type and transition temperature.The spin reorientation near the room temperature is rapid which is expected to be applied to the development and design of room temperature magnetic switching devices.