Room temperature magnetoelectric effects in bulk poly-crystalline materials of M- and Z-type hexaferrites

The converse magnetoelectric effect in poly-crystalline Z-type, Sr3Co2Fe24O41, and M-type, SrCo2Ti2Fe8O19 (SCTFO), hexaferrite materials are reported. The change in remanent magnetization (Mr) for M-SCTFO sintered in oxygen and sintered in air is similar and approximately equals to ∼3% in 13 kV/cm electric field and for Z-type is ∼12% in ∼10 kV/cm electric field. The measured magnetoelectric coupling coefficient, α, values at room temperature for Z-type and M-type hexaferrites sintered in O2 were measured to be 7.6 × 10−10 sm−1 and 2.4 × 10−10 sm−1, respectively. Sintering the M-type in air reduced to 1.7 × 10−10 sm−1. As it is well known, lack of oxygen in local oxygen sites implies lower resistivity and a modified magnetic structures or state. However, in magnetoelectric hexaferrites, there is an additional effect due to lack of oxygen, and the spin spiral configuration is significantly modified to lower the induced magnetization upon the application of a DC voltage or electric field.