Broadband Electron Spin Resonance Study in a Sr₂FeMoO₆ Double Perovskite

Abstract

We report broadband magnetic resonance in polycrystalline Sr 2 FeMoO 6 measured over the wide temperature ( T = 10–370 K) and frequency ( f = 2–18 GHz) ranges. Sr 2 FeMoO 6 was synthesized by the sol–gel method and found to be ferromagnetic below T C = 325 K. A coplanar waveguide-based broadband spectrometer was used to record the broadband electron spin resonance (ESR) both in frequency sweep and field sweep modes. From the frequency sweep mode at fixed dc magnetic fields, we obtain the spectroscopic splitting factor g ∼ 2.02 for T ≥ T C K, which confirms the 3+ ionic state of Fe in the material. The effective g value was found to decrease monotonically with decreasing temperature in the ferromagnetic regime. Resonance frequency decreases and the line width of the spectra increases as the temperature decreases below T C . At room temperature (RT) and above, the line width (Δ H ) of the ESR signal increases linearly with frequency, giving Gilbert damping constant α ∼0.032 ± 0.005 at RT. However, at lower temperatures, a minimum emerges in the Δ H vs frequency curve, and the minimum shifts to a higher frequency with decreasing temperature, confining the linear frequency regime to a narrow-frequency regime. Additional inhomogeneous broadening and low-field-loss terms are needed to describe the line width in the entire frequency range.

Microwave Magnetoresistance and Microwave Absorption in Sr2FeMoO6

“…It is apparent from the M ( T ) curve that the onset of ferromagnetic Curie temperature T C is above 400 K, beyond the high-temperature limit of the PPMS instrument. The T C of the present sample is higher than that of the previous sample prepared by our group under different synthesis conditions . Isothermal M – H hysteresis loops at 5 and 300 K shown in the inset of Figure are typical of a soft ferromagnet with a rapid increase at low fields and a tendency to saturate at H = 70 kOe and 5 K. At 5 K, the coercivity is 153.6 Oe and saturation magnetization is M S = 3.3 μ B /fu at 70 kOe.…”

“…The T C of the present sample is higher than that of the previous sample prepared by our group under different synthesis conditions. 20 Isothermal M−H hysteresis loops at 5 and 300 K shown in the inset of Figure 1 4% for H = 30 kOe). The magnitude of dc MR increases with decreasing temperature and reaches a maximum value of −13.3% at 150 K for H = 30 kOe.…”

“…A pellet needed for the magnetoresistance measurement was annealed in air at 500 °C for 4 h. The pellet was air-annealed at 500 °C instead of 1200 °C since we wanted to investigate the microwave magnetotransport in a sample with more grain boundaries and high resistivity. A Philips X’PERT MPD powder X-ray diffractometer with a Cu Kα (1.542 Å) radiation source was used to record the powder X-ray diffraction pattern, and it confirmed that the sample was single phase and possessed a tetragonal crystal structure (space group I 4/ mmm ) at room temperature . Magnetization and dc four-probe resistivity were measured using a physical property measuring system (PPMS) equipped with a vibrating sample magnetometer.…”

“…A Philips X'PERT MPD powder X-ray diffractometer with a Cu Kα (1.542 Å) radiation source was used to record the powder X-ray diffraction pattern, and it confirmed that the sample was single phase and possessed a tetragonal crystal structure (space group I4/mmm) at room temperature. 20 Magnetization and dc four-probe resistivity were measured using a physical property measuring system (PPMS) equipped with a vibrating sample magnetometer. The dc magnetoresistance (MR) at a given temperature is calculated using the standard definition =…”

Role of site selective substitution, magnetic parameter tuning, and self heating in magnetic hyperthermia application: Eu-doped magnetite nanoparticles

“…Secondly, resonance linewidth H pp or Δ H 1/2 follows the decreasing trend, signifying the strong super-exchange interaction, existence of dipolar–dipolar interaction, and conduction between the Eu 3+ /Fe 3+ –Fe 2+. 30 Moreover, there is a possibility of migration of ions in both tetrahedral and octahedral sites, respectively, which can be seen from cation distribution in the Rietveld refinement analysis. Additionally, the single broad ESR curve at g ∼ 2 directs that characterized MNPs are in the superparamagnetic phase.…”