Tailored tunneling magneto-dielectric effects in Co-MgF₂ granular nanostructures by in-situ insertion of thin MgF₂ layers

We report a Co-MgF/MgF heterostructure that comprises periodic layers of super-paramagnetic Co_0.23-(MgF)_0.77 and thin crystalline MgF, to tailor the frequency response of tunneling magneto-dielectric (TMD) effect. The results indicate that increasing MgF interlayer thickness (t) from 0 to 4 nm causes the position of peak dielectric change (Δε′/ε′₀) at a specific frequency f_TMD, to shift from 300 to 3 kHz, while also retaining a slight decrease in Δε′/ε′₀ from 2.9% to 2.4%. The magnitude of Δε′/ε′₀ can be controlled by varying the Co content in the granular layers. Theoretical curve fittings predict that the TMD effect in the heterostructure arises from both the granular layers and interlayers, and a change in inter-granular distance within the interlayers leads to a shift in the position of f_TMD. This study may prove helpful for tailoring the magneto-dielectric response of granular nanocomposites to a particular frequency, with potential magnetoelectric applications over a wide frequency range.