Strong Converse Magnetoelectric Effect in a Composite of Weakly Ferromagnetic Iron Borate and Ferroelectric Lead Zirconate Titanate

This report is on a model and experiment on the nature of mechanical-strain-mediated converse magnetoelectric (CME) effect in a composite of single-crystal iron borate, a canted antiferromagnet with a weak ferromagnetic moment, and ferroelectric lead zirconate titanate (PZT). The piezoelectric strain generated in PZT by an electric field E manifested as a shift in the quasiferromagnetic resonance (FMR) field in iron borate due to strong magnetoelastic interactions. The CME interaction strength determined from data on field shift in FMR versus E is 46–54 MHz cm/kV at 5.5–6.5 GHz. The strength of the CME is comparable to values reported for composites of ferrimagnetic oxides and PZT. A model that considers the effect of piezoelectric deformation on magnetic order parameters and magnetic resonance in iron borate is proposed for the CMEs in the composite and estimated ME coupling coefficients are in good agreement with data. The E tunability of the high-frequency AFMR mode at about 300 GHz is estimated to be on the order of 1.7 MHz kV/cm and is very small relative to the quasi-FMR mode. Composites of iron borate and ferroelectrics are very attractive for use in dual electric field and magnetic field tunable signal processing devices due to strong CME interactions and the need for a rather small bias magnetic field compared with traditional ferrimagnetic oxide based devices.

Figure 1

(a) Rhombohedral unit cell of ${\mathrm{Fe}\mathrm{BO}}_3$ containing two formula units. Each $\mathrm{Fe}$ atom is surrounded by six oxygen, forming an octahedron, and B atoms are situated in the center of flat oxygen equilateral triangle. (b) Sketch showing directions of sublattice magnetizations ${\overline{M}}_1$ and ${\overline{M}}_2$, weak ferromagnetic moment $\overline{M}$, and antiferromagnetic vector $\overline{l}$. Also, the behavior of $\overline{M}$ and $\overline{l}\mathrm{during}$ quasi-FMR oscillations is schematically shown.

Figure 2

(a) ${\mathrm{Fe}\mathrm{BO}}_3$-PZT bilayer composite structure. (b) Block diagram showing the field sweep wideband ferromagnetic resonance measurement system.

Figure 3

(a) Profiles showing low-frequency quasi-FMR for ${\mathrm{Fe}\mathrm{BO}}_3$ in a composite with PZT. Inset shows the bilayer composite. (b) Frequency versus resonance field H_0r for FMR in the composite. Solid and dashed lines are theoretical fits to the data.

Figure 4

(a) Low-frequency quasi-FMR profiles for ${\mathrm{Fe}\mathrm{BO}}_3$-PZT composite at 5.5 GHz for dc voltages applied to PZT. (b) Variation of the resonance field H_0r as a function of V obtained from profiles shown in (a).

Figure 5

Data on variation in the quasi-FMR resonance field H_0r and its experimental and theoretical variations with V for frequencies of 5.5, 6, and 6.5 GHz.