Growth And Low Temperature Magnetoelectric Characteristics Of CaBaFe₄O₇ Single Crystals

Multiferroic material is a new type of quantum functional material with two or more ferrites at the same time,which can realize the control of the electric field?or magnetic field?on the sample magnetization?or polarization?,so as to develop the next generation of high efficiency and energy saving Multifunctional devices are of great significance.Exploring the internal mechanism of magnetoelectric coupling materials with high phase transition temperature has always been the frontier and hot spot in this field.In recent years,it has been found that sodamonite in the form of ABM₄O₇?M is a magnetic ion?represents a new type of polar magnet.In this polar magnet,the ferrimagnetic order is at a relatively high temperature.Happened,and found that CaBaFe₄O₇?CBFO?has a rich magnetoelectric coupling effect.In this paper,the CBFO single crystal is taken as the research object.The origin of the magnetoelectric coupling effect in the CBFO single crystal is explored by measuring the magnetoelectricity,magnetoelectricity,and magnetostriction of the sample under variable temperature or magnetic field conditions.The specific research results are as follows:?1?About the improvement of CBFO single crystal floating zone process.The single crystal is prone to Ca Ba Fe₄O₈ phase in the preparation process,and at the same time,it is also prone to bubbles,twins and defects.In order to obtain single-phase CaBaFe₄O₇ polycrystalline ceramic powder,we used a mixed gas of 5% H₂+95% Ar to prepare polycrystalline ceramic powder to ensure the proportion of Fe²⁺ in CaBaFe₄O₇ polycrystalline ceramic powder.When using the floating zone method to grow single crystals,through the exploration of the rotation speed of the polycrystalline rod,the feeding speed and the temperature of the floating zone,it was found that when the rotational speed of the polycrystalline rod is 30 r/min and the feed rate is 1 mm/h The quality of the prepared single crystal is the highest.By studying the magnetization curve?M-H?of the CBFO single crystal and the magnetization?M-T?in different directions,we know that the CBFO single crystal is a ferrimagnetic magnet with a magnetic phase transition temperature of Tc=273 K.Below the magnetic ordering temperature,the magnetization in the direction of the easy axis increases rapidly with decreasing temperature,and at 211 K there is a small peak due to the spin reorientation of the magnetic moment.The magnetization intensity perpendicular to the c-axis is obviously smaller than that along the c-axis,but the variation of the magnetization with the magnetic field is consistent with that along the c-axis,indicating that the magnetic moment is more along the c-axis direction,and may also exist in the ab plane Ferromagnetic component.According to the analysis of the above test data,we reasonably guess that the magnetic structure of the CBFO single crystal may be: the spins form a helical chain magnetic moment along the c-axis in the c-axis direction,and the antiferromagnetic arrangements are inclined to each other in the ab plane.?3?We discovered the magnetic transition and polarization of CBFO single crystal and determined that the polarization of CBFO single crystal is derived from lattice distortion.Through the magnetostriction of the test samples,we found that the CBFO single crystal shrinks as the magnetic field increases to a certain magnetic field,the material shrinks,and the crystal is distorted,causing the internal charge distribution to deviate from the charge center and appear polarized.The magnetostrictive test confirmed our speculation that it was indeed the magnetoelectric effect of CBFO single crystal due to crystal distortion.The lattice distortion is probably caused by exchange.