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.

The room-temperature multiferroic and magnetocapacitance (MC) effects of polycrystalline M-type hexaferrite BaFe_10.2Sc_1.8O₁₉ have been investigated. The results show that the magnetic moments of insulating BaFe_10.2Sc_1.8O₁₉ can be manipulated by the electric field at room temperature, indicating the existence of magnetoelectric coupling. Moreover, large MC effects are also observed around the room temperature. A frequency dependence analysis shows that the Maxwell-Wagner type magnetoresistance effect is the dominant mechanism for MC effects at low frequencies. Both the magnetoelectric-type and non-magnetoelectric-type spin-phonon couplings contribute to the MC effects at high frequencies with the former being the dominant mechanism. The above results show that the hexaferrite BaFe_10.2Sc_1.8O₁₉ is a room-temperature multiferroic material that can be potentially used in magnetoelectric devices.

The impedance spectroscopy of Z-type hexaferrite Sr₃Co₂Fe₂₄O₄₁ (SCFO) has been investigated as a function of temperature from 303 to 503 K. The frequency dependent impedance ($Z^{″}$ ) and modulus ($M^{″}$ ) spectra show that for the air annealed SCFO, the electrical responses of SCFO are thermal activated and 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. The Cole-Cole plots in impedance formalism show that the electrical response of SCFO originates from both the grain and the grain-boundaries. The activation energies for grain and grain boundary are 0.66 eV and 0.67 eV, respectively. The frequency dependent conductivity (${\sigma }^{\prime }$ ) spectra follow the universal power law. The fitting results of ${\sigma }^{\prime }$ spectra show that the small polaron hopping is the most probable conduction mechanism for SCFO. Moreover, the scaling behavior of ${\sigma }^{\prime }$ spectra further confirms that the distribution of local electrical response times is temperature independent. The air plus O₂ annealed SCFO shows thermally activated electrical responses and scaling behaviors as well. The above results show that although the electrical responses of SCFO are temperature dependent, the relaxation mechanism in SCFO is temperature independent.

Recent success in exfoliating violet or Hittorf's phosphorus down to monolayer reignites the research passion in this ancient yet mysterious material, questing for superior electronic and optoelectronic functionalities. Unfortunately, the poor air stability that plagues black phosphorus also exists in the violet counterpart. Aiming to provide more insight into the degradation chemistry and accordingly find a facile solution for it, herein, we employ concerted elemental, chemical and vibrational spectroscopies to reveal the critical role of oxygen and water in the degradation mechanism and pathway of violet phosphorus in ambient condition. Thereafter, a simple passivation approach by oxide encapsulation is demonstrated to realize air-stable violet phosphorus photodetector device. As the proof-of-concept, the photodetector fabricated accordingly shows superior figures of merit with ultralow dark current (< 10−13 A), high low-light responsivity (6 A W−1) and fast response time (< 10 ms) in the ultraviolet to visible spectrum, as well as great chemical robustness against harsh environments.

This work reports a comprehensive investigation of the temperature dependence of the interlayer exchange coupling in the antiferromagnetic coupling of a FeNi/Ru/FeNi trilayer sample using broadband ferromagnetic resonance. The temperature dependence of the interlayer exchange coupling fields is obtained by applying Kittel fitting to the systematic frequency dependence of the resonance field between the acoustic and optic modes and by assuming equal effective magnetization of the two resonance modes. It is found that the value of the exchange coupling field increases with decreasing temperature, showing excellent agreement with the existing theories regarding the spacer and interface and the thermal excitations of the spin wave contributions to the temperature dependence. Additionally, the temperature dependence of the Gilbert damping coefficient was investigated for the acoustic and optic modes, where the optic mode damping coefficient was markedly different from and greater than of the acoustic mode. These results provide important information that will be helpful in the understanding of antiferromagnetic resonance.