Kinetics and Thermodynamics of the Degree of Order of the B Cations in Double-Perovskite Sr₂FeMoO₆

Abstract

Here we show that the B-site cation (Fe/Mo) ordering in the double-perovskite magnetoresistor, Sr 2 FeMoO 6 , is controlled by either kinetics or thermal equilibrium depending on the temperature range. In order to enhance the ordering, long synthesis periods at moderate temperatures are thus required. Employment of a special oxygen-getter-controlled low-O 2 -pressure encapsulation technique for the sample synthesis enabled us to use long heating periods without evident evaporation of Mo, and thereby reach the thermal equilibrium state and a high degree of B-site cation order. For samples fired at 1150 o C for long periods (≥ 36 hours), record-high M S values of 3.7 ∼ 3.9 µ B were obtained.

Competition between intragranular and intergranular tunneling magnetoresistance in polycrystallineSr2FeMoO6

“…As reported in our previous works, sintering at 1150°C facilitates a low w value due to thermal equilibrium. 15,17 For a sample sintered at 1150°C, w is about 0.05 for t s = 4 h, 0.03 for 24 h, and as low as 0.02 for 100 h. Resistivity at zero field as a function of temperature for the SFMO samples is presented in Fig. 3.…”

“…[12][13][14] A certain density of DODs remains unavoidably on the octahedral B-cation sublattice in SFMO after a finite sintering period owing to the slow kinetics of the ordering process. 15 In SFMO, a long-range magnetic interaction between the spins of Fe 3+ ͑S =5/2͒ and Mo 5+ ͑S =1/2͒ induces the ferromagnetic half-metallic state with a theoretical saturation magnetization ͑M s ͒ of 4 B per formula unit. With the existence of DODs, the M s value should be lowered due to the antiferromagnetic interaction between the adjacent Fe ions.…”

Magnetization-steps in Y2CoMnO6 double perovskite: The role of antisite disorder

“…Specific synthesis routes with controlled heating and cooling rates which control the kinetics of the reaction are essential to obtain samples with high degree of cationic order. 12,33 The polycrystalline samples used in the present study were prepared by fast rates of firing and cooling at elevated temperatures and hence resulted in higher content of disorder.…”

Reversible Low‐Field Magnetoresistance in Sr2Fe2–xMoxO6–δ by Oxygen Cycling and the Role of Excess Mo (x > 1) in Grain‐Boundary Regions

“…[1] It therefore has promise for applications in spintronics and magnetic sensors. There have been numerous reports of optimization of processing conditions to yield high levels of cation ordering [2,3] and crystalline perfection, which are required to yield the theoretical saturation magnetization value of 4l B per formula unit (where l B is the Bohr magneton).…”