The dielectric properties of Z-type hexaferrite Sr₃Co₂Fe₂₄O₄₁ (SCFO) have been investigated as a function of temperature from 153 to 503 K between 1 and 2 GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 10⁸ Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z″) and modulus (M″) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 10⁸ Hz. A comparison between the Z″ and the M″ spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior.

Magnetic and electronic transport properties of perovskite manganite La_0.6Er_0.1Sr_0.3MnO₃ have been thoroughly examined through the measurements of magnetization, electron paramagnetic resonance(EPR), and resistivity. It was found that the substitution of Er³⁺ for La³⁺ ions introduced the chemical disorder and additional strain in this sample. An extra resonance signal occurred in EPR spectra at high temperatures well above T _C gives a strong evidence of electronic phase separation(EPS). The analysis of resistivity enable us to identify the polaronic transport mechanism in the paramagnetic region. At low temperature, a new ferromagnetic interaction generates in the microdomains of Er³⁺-disorder causing the second increase of magnetization. However, the new ferromagnetic interaction does not improve but decreases electronic transport due to the enhancement of interface resistance among neighboring domains. In view of a really wide temperature region for the EPS existence, this sample provides an ideal platform to uncover the evolution law of different magnetic structures in perovskite manganites.

Electrostatic dielectric capacitors with ultrahigh power densities are sought after for advanced electronic and electrical systems owing to their ultrafast charge-discharge capability. However, low energy density resulting from low breakdown strength and suppressed polarization still remains a daunting challenge for practical applications. We propose a microstructural strategy with dendritic nanopolar (DNP) regions self-assembled into an insulator, which simultaneously enhances breakdown strength and high-field polarizability and minimizes energy loss and thus markedly improves energy storage performance and stability. For illustration, in this study, we achieved a high energy density of 215.8 joules per cubic centimeter with an efficiency of 80.7% at a high electric field of 7.4 megavolts per centimeter in a DNP structure–designed PbZr _0.53 Ti _0.47 O ₃ -MgO film. The proposed strategy is generally applicable for development of high-performance dielectric microcapacitors.

Negative pressure has emerged as a powerful tool to tailor the physical properties of functional materials. However, a negative pressure control of spin-phonon coupling for engineering magnetism and multiferroicity has not been explored to date. Here, using uniform three-dimensional strain-induced negative pressure in nanocomposite films of (EuTiO₃)_0.5:(MgO)_0.5, we demonstrate an emergent multiferroicity with magnetodielectric coupling in EuTiO₃, matching exactly with density functional theory calculations. Density functional theory calculations are further used to explore the underlying physics of antiferromagnetic-paraelectric to ferromagnetic-ferroelectric phase transitions, the spin-phonon coupling, and its correlation with negative pressures. The observation of magnetodielectric coupling in the EuTiO₃ reveals that an enhanced spin-phonon coupling originates from a negative pressure induced by uniform three-dimensional strain. Our work provides a route to creating multiferroicity and magnetoelectric coupling in single-phase oxides using a negative pressure approach.

Self-assembled nanocomposite thin films couple two materials into a single film, typically, in the form of vertically aligned nanopillars embedded in a matrix film. High-density vertical heterointerfaces provide a great platform for engineering new physical properties and novel multifunctionalities, as well as for nanoscale device integration. Tremendous research efforts have been devoted to developing different nanocomposite systems. In this article, we summarize recent progress on vertically aligned nanocomposite thin films for enhanced functionalities such as ferroelectricity, tunable magnetoresistance, multiferroicity, dielectricity, magnetic anisotropy, perpendicular exchange bias, novel electrical/ionic properties, interfacial conduction, and resistive switching. Using specific examples, we discuss how and why the fundamental physical properties can be significantly tuned/improved in vertically aligned nanocomposites. Finally, we propose future research directions to achieve further enhanced performance as well as practical devices.