Magnetic properties of the magnetoelectricAl2−xFexO3 (x = 0.8,0.9 and 1)

Abstract

By using x-ray diffraction, magnetization and Mössbauer spectroscopy techniques we have studied themagnetoelectric Al2−xFexO3 (x = 0.8,0.9 and1.0) compound. Ac-susceptibility and magnetization measurements revealed magnetic transitions atTN = 180,210 and260 K for x = 0.8, 0.9 and 1.0 respectively, that can be attributed to the Néel temperatures of ferrimagneticto paramagnetic phase transition for all samples. Mössbauer spectra for the three sampleswere recorded between 4.2 and 295 K. Above the Néel temperature the paramagnetic spectracan be analyzed by three quadrupole doublets associated with the octahedral Fe1, Fe2 andFe4 sites. The values of the hyperfine parameters show that iron ions are in the high spinFe3+ state. The spectrum area of the doublet with larger quadrupole splitting increases withx, andin combination with x-ray diffraction results it can be attributed to the iron which occupies the Fe4 site.Below TN(x) the Mössbauer spectra are magnetically split and atT = 4.2 K consist of six broad lines, indicating either a hyperfine magnetic field distribution(P(Hhyp)) or that the three octahedral sites give three unresolved sextets. The most probable value ofHhyp (the maximumvalue of P(Hhyp)) follows a power law indicative of a second order transition, in agreementwith ac-susceptibility and magnetization measurements. The width ofP(Hhyp) increases drastically toward low hyperfine magnetic fields as temperature increases. In addition,an appreciable percentage of the iron nuclei sense a hyperfine field with values in the interval[0,Hmax]. This behavior can be explained by assuming that several magnetic sites with differentsuperexchange parameters exist.