SPIN-GLASS BEHAVIOR IN AMORPHOUS BIFEO3

Short-range antiferromagnetic (speromagnetic) behavior was observed for amorphous BiFeO3 by static magnetic measurements, ac susceptibility (chi(ac)) measurement, and Fe-57 Mossbauer spectra measurements. The magnetic behavior is classified into three temperature ranges: (i) paramagnet for T > 220 K; (ii) local clustering of spins for 20 K < T < 220 K; and (iii) speromagnet in which all spins are frozen into random directions for T < 20 K. In the spin freezing state the magnetization shows irreversibility and the chi(ac) - T curve has a cusp. The variation of the spin freezing temperature against measuring magnetic field and measuring frequency indicate that the speromagnetic order is very similar to that of spin glass.