| Ba2FeMoO6 exhibits a ferromagnetic to paramagnetic transition with a Curie temperature above room temperature,and its high temperature superconducting,room temperature tunneling magnetoresistance effect and multiferroic properties has a good application value in the field of spintronics.The B-site long range cation order degree of A2FeMoO6 will affect the magnetic properties of these materials.A conventional comparative analysis of lattice parameter data from present study and literature reports in terms of spontaneous strain shows that the magnetic ordering is accompanied by a significant volume strain,which indicates a strong coupling behavior of magneto–elastic properties in Ba2FeMoO6.In this paper,Ba2FeMoO6 is selected as the research focus.To address the correlation between B-site long range cation order degree and magnetic properties,a comparative study of Ba2FeMoO6 polycrystals with different degrees of ASD was carried out by XRD,Rietveld refinement and quantum interferometer.Moreover,The relationship between magnetism and strain of Ba2FeMoO6 is predicted and verified from the point of view of strain by space group theory,Landau theory and in-situ XRD.The results show that:The double perovskite Ba2FeMoO6 polycrystalline ceramic powder prepared by the conventional solid phase sintering method has a cubic structure?Fm3 m,No.225?by X-ray powder diffraction and Rietveld refinement.When calcination time was 15 h,pure phase Ba2FeMoO6 was synthesized;the Curie temperature?Tc?of the sample synthesized at 1273 K decreased slightly from325.85K to320.87 K.As the synthesis temperature increased from 1273 K to 1573 K,Tc decreased significantly from320.87 K to278.88 K.This indicates that the synthesis temperature has an important influence on Tc;As the ASD decreased from16%to 10%,the low-temperature saturation magnetization?Ms?increased from 2.53?B/fu to 3.53?B/f.u..When the synthesis temperature increased to 1373 K,the Ms of the sample decreased although the ASD decreased to 4.7%.As the ASD increased to6.7%,Ms is further reduced to 2.97?B/f.u..Increasing the sintering time can improve the uniformity of the sample grains,and the sintering temperature has an important effect on the grain size;The shear strain?et?and volumetric strain?ea?of Ba2FeMoO6and the magnetic order parameter?m32?are linearly related by the Landau theory.The coupling strength depends on the coupling coefficient??2??4?,and the results of this calculation were verified experimentally;The ASD of the spark plasma sintered sample was 0,and its Tc and Ms were 309.53 K and 2.09?B/f.u.,respectively.The annealed samples had an ASD of 0.05 with Tc and Ms of 320.61 K and 2.77?B/f.u.,respectively.It indicates that annealing has an important influence on the Tc and Ms of the sample.Annealing can improve the uniformity of sample grains. |
PDF Full Text Request