Magnetoelectric effect in nanogranular FeCo-MgF films at GHz frequencies.

•Magnetoelectric effect in the nanogranular FeCo-MgF films has been investigated.•Magnetoelectric effect and dielectric relaxation are confirmed at frequencies over 10MHz.•The inter-spacing of granules and the relaxation time decrease with increasing magnetic metal concentration.•The magnetoelectric effect reaches a maximum at a relaxation frequency.