Large low field room temperature magneto-dielectric response from (Sr0.5Ba0.5)Nb2O6/Co(Cr0.4Fe1.6)O4 bulk 3-0 composites

Bulk magneto-dielectric composites with a 3-0 configuration comprised of ferroelectric-magnetostrictive phases have been synthesized using (Sr0.5Ba0.5)Nb2O6-Co(Cr0.4Fe1.6)O4 as the two constituents, respectively. The ferroelectric phase made by a dual stage sintering process has a uniform grain size of 15 μm while the magnetostrictive phase has a grain size of 2-3 μm. Composites synthesized by conventional solid state processing using these two constituents exhibit large magneto-dielectric coupling at room temperature which increases with increasing magnetic field. The composite with 30% magnetostrictive phase distributed uniformly in the ferroelectric phase has the most desirable microstructure and exhibits a large coupling with 3.2% change in the dielectric constant at 1 kHz and 8 kOe magnetic field. This change in dielectric constant was found to be a maximum with respect to variation of the fraction of magnetostrictive phase, indicating that 30% is the optimal value to realize large coupling between the two phases. The decrease in magneto-dielectric constant upon application of an external magnetic field is possibly due to the inherent magnetoresistance of the magnetic component. The resistivity of the magnetic component decreases in an external magnetic field leading to the formation of 3D percolating conducting paths. This causes the coupling to decrease in composites with >30% magnetostrictive phase.