Magnetic And Magnetoelastic Coupling Properties Of Double Perovskites A₂FeReO₆（A=Ca,Sr,Ba）

Re-based double perovskite oxides have rich physical properties,such as high Curie temperature,magnetoresistance effect,Coulomb interaction,and half-metallic behavior,which have potential application value in many fields.In this article,the A₂Fe Re O₆（A=Ca,Sr,Ba）series of double perovskites were prepared by high-temperature solid-phase reaction,and the influence of annealing time on their magnetic properties was explored.The strain,magnetoelastic coupling,and elastic relaxation properties of Ba₂Fe Re O₆were also investigated.Investigations of elastic and anelastic properties were mainly done by Resonant Ultrasound Spectroscopy（RUS）.RUS is a powerful tool to observe how the elasticity and hysteresis vary with temperature.This article provides a detailed introduction the equipment and the corresponding analytical method.The main research contents and results of this paper are as follows:1.A₂Fe Re O₆（A=Ca,Sr,Ba）double perovskite was successfully synthesized using ACO₃（A=Ca,Sr,Ba）,Fe and Fe₂O₃as raw materials by high temperature solid phase method.The preparation method used in this paper improves the success rate by synthesizing the precursor A₂Re O_5.5.On this basis,the changes of magnetic properties of the material are investigated when the annealing time is 5 hours,2 days and 5 days respectively.The results shows that the magnetic properties of the sintered sample are more excellent when the annealing time is 2 days.2.Strain coupling and relaxation dynamics associated with the ferrimagnetic/ferroelastic phase transition at T_c≈310 K in double perovskite Ba₂Fe Re O₆with a high degree of Fe/Re order have been investigated by resonant ultrasound spectroscopy through the temperature interval～5-600 K and with applied magnetic field of up to±2 T.Strain analysis using diffraction data from the literature is consistent with a Landau model of the transition as Fm3 m1’→I4/mm’m’,improper ferroelastic,driven by a magnetic order parameter with symmetryΓ₄⁺.Ferroelastic shear strain of up to～0.0015 arises from spin/orbit coupling,it is than the shear strain caused by the typical coupling with octahedral tilting.It provides the underlying cause of softening of the shear modulus observed over an interval of～100 K below T_c,though with order/disorder rather than displacive character for the transition.Hysteretic effects suggest that precursor microstructures and mixed magnetic/ferroelastic domains below T_cdepend on the thermal history of the sample and can evolve on a time scale of hours and days at room temperature.Elasticity data collected as a function of external magnetic field reveal that poled samples are slightly softer than those with multiple magnetic domains at 4 K.At 300 K there is a time dependent viscous component of the response to the field that relates to the bulk modulus and,hence,to volume changes associated with magnetic ordering.In summary,Ba₂Fe Re O₆is a material with magnetoelastic and magnetoelectric heterogeneities that might be tuned by choice of thermal history and cation order.