Acoustic properties of multiferroics PbFe1/2Ta1/2O3 and BiFeO3 at Néel temperature

The longitudinal acoustic wave velocity and attenuation in PbFe
_1/2
Ta
_1/2
O
₃
and BiFeO
₃
ceramics have been measured by ultrasonic pulse-echo technique in the temperature range from 50 K to 530 K and from 250 K to 830K, respectively. The anomalies observed in the sound velocity behavior versus temperature in the case of PbFe
_1/2
Ta
_1/2
O
₃
were correlated with Burns temperature and temperature range of relaxor ferroelectric and antiferromagnetic states coexistence. BiFeO
₃
demonstrates wide minimum of acoustic wave velocity at Neél temperature. Magnetostriction along with order parameter fluctuations are discussed as the factors determining the acoustic wave velocity anomaly in the vicinity of the antiferromagnetic phase transition point.