RESUMO
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 (TN), 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 Co0.65Zn0.35Fe2O4 (CZFO). Rietveld refinement of X-ray diffraction patterns confirms the phase purity with a cubic crystal structure with the (Fd3[combining macron]m) 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 (TN) 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 â¼640 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.
RESUMO
Multiferroic materials have attracted considerable attention as possible candidates for a wide variety of future microelectronic and memory devices, although robust magnetoelectric (ME) coupling between electric and magnetic orders at room temperature still remains difficult to achieve. In order to obtain robust ME coupling at room temperature, we studied the Pb(Fe0.5Nb0.5)O3/Ni0.65Zn0.35Fe2O4/Pb(Fe0.5Nb0.5)O3 (PFN/NZFO/PFN) trilayer structure as a representative FE/FM/FE system. We report the ferroelectric, magnetic and ME properties of PFN/NZFO/PFN trilayer nanoscale heterostructure having dimensions 70/20/70 nm, at room temperature. The presence of only (00l) reflection of PFN and NZFO in the X-ray diffraction (XRD) patterns and electron diffraction patterns in Transmission Electron Microscopy (TEM) confirm the epitaxial growth of multilayer heterostructure. The distribution of the ferroelectric loop area in a wide area has been studied, suggesting that spatial variability of ferroelectric switching behavior is low, and film growth is of high quality. The ferroelectric and magnetic phase transitions of these heterostructures have been found at ~575 K and ~650 K, respectively which are well above room temperature. These nanostructures exhibit low loss tangent, large saturation polarization (Ps ~ 38 µC/cm2) and magnetization (Ms ~ 48 emu/cm3) with strong ME coupling at room temperature revealing them as potential candidates for nanoscale multifunctional and spintronics device applications.