| Magnetoelectric (ME) materials are capable of converting a magnetic field into an electric field and vice-versa and are considered to be an important futuristic, progressive entity for making sensor, processors, actuators and feedback system. In the present work, the magnetoelectric composites with a typical relaxor with tungsten-bronze structure, Sr0.5Ba0.5Mb2O6 and its solid solution, as piezoelectric phase and Co-spinel as piezomagnetic phase were prepared and characterized to explore new magnetoelectric materials.Novel composites were created through incorporating dispersed CoFe2O4 ferromagnetic grains into Sr0.5Ba0.5Nb2P6 relaxor ferroelectric matrix. The two phases are chemically compatible and co-exist in the dense, sintered composites. The apparent dielectric constant is enhanced by the conductivity in the ferrite phase and the space charge on the phase interface. All composites after post-densification annealing in oxygen could be electrically and magnetically poled to exhibit significant magnetoelectric effect. Significant effect was observed in all compositions investigated, a maximum dE/dH value of 24.8mV/cm/Oe for 0.6Sr0.5Ba0.5Nb2O6/0.4CoFe2O4. The ME effect of the composites was greatly dependent on the frequency of a.c. magnetic field. With increasing frequency, the magnetoelectric coefficient dE/dH increased firstly and then decreased.Ba0.55Sr0.25Ca0.2Nb2O6/CoFe2O4 magnetoelectric (ME) composites were also prepared and characterized. Co-presence of two end-members was confirmed. A very high dielectric constant was obtained at low frequencies and an interesting temperature dependence of dielectric constant was observed in the present composite ceramics. The ME effect of the composites was greatly dependent on the frequency of a.c. magnetic field. With increasing frequency, the magnetoelectric coefficient dE/dH increased firstly and then decreased. dE/dH also depended on the d.c bias magneticfield. The highest dE/dH value of 9.51mV/cm/Oe was observed in 0.8Ba0.55Sr0.25Ca0.2Nb2O6/0.2CoFe2O4 composites under 1 kOe and at 90 kHz. |
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