Magnetoelectricity in BiFeO3 and BiFe0.98Co0.02O3 nano particles.

Room temperature magnetoelectric (ME) measurements are carried out on phase pure BiFeO 3 and BiFe 0.98 Co 0.02 O 3 , prepared via sol–gel technique. At zero magnetic field, the longitudinal ME coupling coefficient ( α ) for BiFeO 3 is found to be α = 20.935, which decreases on application of magnetic field and displays hysteresis in magnetic field ( H ) for the increasing and decreasing cycle of H . This hysteresis disappears for BiFe 0.98 Co 0.02 O 3 and α becomes linear in H along with 17% drop in the magnitude compared to parent BiFeO 3 . In spite of 17% drop, magnitude of α = 17.375 is good enough for device applications especially where α must follow the applied magnetic field linearly, e.g., transistors, transducers, etc. Neutron diffraction studies show lattice stiffening due to cobalt substitution in BiFeO 3 and likely to be the cause of disappearance of hysteresis in α . Calculated value of polarization P (using the parameters derived from neutron diffraction) shows 19% drop in magnitude of P for cobalt substituted sample. Surprisingly, dielectric measurements also showed 18% decrease in dielectric constant ɛ ′ due to cobalt doping. Such a one to one correspondence in the three parameters viz., α , P and ɛ ′, reflects a strong interdependence so that variation in any one of them is reciprocated in the other. Room temperature magnetodielectricity of 5% and 3.2% is observed for BiFeO 3 and BiFe 0.98 Co 0.02 O 3 respectively. Interestingly similar to α , ɛ ′ also shows hysteresis in magnetic field for BiFeO 3 and the hysteresis disappears for BiFe 0.08 Co 0.02 O 3 . The dc electrical resistivity measurements, suggests variable range hopping (VRH) with average hopping range 50.038/ T 0.25 and 40.058/ T 0.25 in BiFeO 3 and BiFe 0.98 Co 0.02 O 3 respectively, as the conduction mechanism. [ABSTRACT FROM AUTHOR]