Crystal structural, dielectrical properties and high temperature magnetic phase transition of Sm1-xCaxFeO3 (x=0-0.3)

In the present study, crystal structural, dielectric, ferromagnetic properties and high temperature magnetic phase transition of Sm1-xCaxFeO3 (x = 0-0.3) by the conventional solid-state reaction method were investigated. The crystalline structure, the microstructure, the dielectric property of the Sm1-xCaxFeO3 samples was characterized by x-ray diffraction (XRD) and field emissions canning electron microscopy (FESEM). The dielectric property measurement was performed by a precision impedance analyzer with the frequency range from 40 to 110 MHz. The coexistence of Fe3+/2+ ions in Sm1-xCaxFeO3 samples was investigated with X-ray photoelectron spectroscopy (XPS). The magnetic property of Sm1-xCaxFeO3 was measured with Physical Property Measurement System (PPMS). The result shows that all the peaks for Sm1-xCaxFeO3 samples can be indexed according to the crystal structure of pure SmFeO3 and has a fine crystal structure by XRD. The SEM images indicate that Ca2+ doping significantly increases the grain sizes of SmFeO3 ceramic. The average grain sizes of Sm1-xCaxFeO3 samples range from 0.5 to 2 μm with Ca2+ doping. εr of Sm1-xCaxFeO3 measured at 1 kHz is about 5, 3 and 2.6 times greater than that of SmFeO3, respectively, and the dielectric loss increases by an order of magnitude. The increase of εr is mainly caused by the interaction between the dipole and the space charge orientation polarization. Magnetic measurements show that the M-H of Sm1-xCaxFeO3 samples exhibit saturated magnetic hysteresis loops with the increase of Ca2+, and the Mr of Sm1-xCaxFeO3 (x = 0-0.3) is 20, 31, and 68 times of that of SmFeO3, respectively, suggesting the weakly ferromagnetic behavior. The XPS spectrum indicates the coexistence of Fe2+ and Fe3+ in Sm1-xCaxFeO3 samples. The ratio of Fe2+/Fe3+ presents a growing trend with the increase of Ca2+ doping. It can be attributed to the structural distortion and the formation of Fe2+-O2--Fe3+ super-exchange. The spin recombination temperature (TSR) and Neel temperature (TN) are 437 K, 687 K by measuring the M-T curves. It is noted that both TSR and TN of SmFeO3 samples move towards the low temperature with the increase of x, and the spin recombination disappear when x = 0.3. This is primarily due to the stability of the magnetic structure of SmFeO3 and the interaction of Fe3+-O2--Fe3+ and Sm3+-O2--Fe3+ super-exchange.