Multiferroic (MF)-magnetoelectric (ME) composites, which integrate magnetic and ferroelectric materials, exhibit a higher operational temperature (above room temperature) and superior (several orders of magnitude) ME coupling when compared to single-phase multiferroic materials. Room temperature control and the switching of magnetic properties via an electric field and electrical properties by a magnetic field has motivated research towards the goal of realizing ultralow power and multifunctional nano (micro) electronic devices. Here, some of the leading applications for magnetoelectric composites are reviewed, and the mechanisms and nature of ME coupling in artificial composite systems are discussed. Ways to enhance the ME coupling and other physical properties are also demonstrated. Finally, emphasis is given to the important open questions and future directions in this field, where new breakthroughs could have a significant impact in transforming scientific discoveries to practical device applications, which can be well-controlled both magnetically and electrically.

Multiferroic composite structures, i.e., composites of magnetostrictive and piezoelectric materials, can be envisioned to achieve the goal of strong room-temperature ME coupling for real practical device applications. Magnetic materials with high magnetostriction, high Néel temperature (T_N), high resistivity and large magnetization are required to observe high ME coupling in composite structures. In continuation of our investigations on suitable magnetic candidates for multiferroic composite structures, we have studied the crystal structure, dielectric, transport, and magnetic properties of Co_0.65Zn_0.35Fe₂O₄ (CZFO). Rietveld refinement of X-ray diffraction patterns confirms the phase purity with a cubic crystal structure with the (Fdm) space group; however, we have found a surprisingly large magneto-dielectric anomaly at the Néel temperature, unexpected for a cubic structure. The presence of mixed valences of Fe²⁺/Fe³⁺ cations is probed by X-ray photoelectron spectroscopy (XPS), which supports the catonic ordering-mediated large dielectric response. Large dielectric permittivity dispersion with a broad anomaly is observed in the vicinity of the magnetic phase transition temperature (T_N) of CZFO suggesting a strong correlation between dielectric and magnetic properties. The evidence of strong spin-polaron coupling has been established from temperature dependent dielectric, ac conductivity and magnetization studies. The ferrimagnetic–paramagnetic phase transition of CZFO has been found at ∼640 K, which is well above room temperature. CZFO exhibits low loss tangent, a high dielectric constant, large magnetization with soft magnetic behavior and magnetodielectric coupling above room temperature, elucidating the possible potential candidates for multiferroic composite structures as well as for multifunctional and spintronics device applications.

We report the crystal structure, magnetic, ferroelectric, dielectric, and magneto-dielectric properties of [Pb(Fe_0.5Nb_0.5)O₃]_(1−x)[Co_0.65Zn_0.35Fe₂O₄]_x: (x = 0.1, 0.2, 0.3, and 0.4) composites. Rietveld refinement results of X-ray diffraction patterns confirm the formation of these composites for all x values. All the composites show well-saturated ferroelectric and ferromagnetic hysteresis (multiferroic-composite behavior) at room temperature. With increase in Co_0.65Zn_0.35Fe₂O₄ (CZFO) content an increase in saturation magnetization, and decrease in saturation polarization, remanent polarization, and dielectric constant are observed. The ferroelectric phase transition temperature increases with increase in CZFO content. All of the compositions undergo second-order ferroelectric phase transitions, which can be explained by Landau-Devonshire theory. The recoverable energy density (∼0.20 to 0.04 J/cm³) and charge-curve energy density (∼0.84 to 0.11 J/cm³) decrease with increase in the CZFO content. The room-temperature magneto-dielectric measurements provide direct evidence of magneto-electric coupling via strain at room temperature.