We report here realization of ferroelectricity, ferromagnetism and magnetocapacitance effect in singleSrFe12O19ceramic at room temperature. The ceramics demonstrate a saturated polarization hysteresis loop, two nonlinear I-V peaks and large anomaly of dielectric constant near Curie temperature, which confirm the intrinsic ferroelectricity of SrFe12O19 ceramicswith subsequent heat-treatment in O2atmosphere. The remnant polarization of the SrFe12O19 ceramic is estimated to be 103μC/cm2. The ceramic also exhibits strong ferromagnetic characterization, the coercive field and remnant magnetic moment are 6192Oe and 35.8emu/g, respectively. Subsequent annealing SrFe12O19 ceramics in O2 plays a key role on revealing its intrinsic ferroelectricity and improving the ferromagnetism through transforming Fe2+ into Fe3+. By applying a magnetic field, the capacitance demonstrates remarkable change along with B field, the maximum rate of change in ε (Δε(B)/ε(0)) is 1174%, which reflects a giant magnetocapacitance effect in SrFe12O19. XPS and molecular magnetic moment measurements confirmed the transformation of Fe2+ into Fe3+ and removal of oxygen vacancies upon O2 heat treatment. These combined functional responses in SrFe12O19 ceramics opens substantial possibilities for applications in novel electric devices.

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The thermoelectric, phonon transport, and electronic transport properties of two-dimensional magnet CrI 3 are systematically investigated by combining density functional theory with Boltzmann transport theory. A low lattice thermal conductivity of 1.355 W m −1 K −1 is presented at 300 K due to the low Debye temperature and phonon group velocity. The acoustic modes dominate the lattice thermal conductivity, and the longitudinal acoustic mode has the largest contribution of 42.31% on account of its relatively large phonon group velocity and phonon lifetime. The high band degeneracy and the peaky density of states near the conduction band minimum appear for the CrI 3 monolayer, which is beneficial for forming a significantly increased Seebeck coefficient (1561 µV K −1 ). Furthermore, the thermoelectric figure of merit is calculated reasonably, and the value is 1.57 for the optimal n-type doping level at 900 K. N-type doping maintains a higher thermoelectric conversion efficiency than p-type doping throughout the temperature range, while the difference gradually increases as the temperature rises. Our investigation may provide some theoretical support for the application of the CrI 3 monolayer in the thermoelectric field.

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The room-temperature intrinsic ferromagnetism of monolayer VSe 2 with a van der Waals gap provides an exciting opportunity for both the fundamental studies and future low-dimensional spintronic devices. By applying biaxial strain, the tunable electronic, magnetic, and phonon transport properties of the VSe 2 monolayer are systematically investigated via first-principle calculations. With in-plane easy magnetization axis, the VSe 2 monolayer is always a robust room-temperature ferromagnetic semiconductor in the strain range from -2 to 4%. According to the second-order perturbation theory of spin-orbital coupling, magnetic anisotropy energy is mainly contributed by the interaction between Vd xy orbital and V-d x 2 Ày 2 orbital. The Curie temperature increases significantly with increasing biaxial strain, from 303 to 469 K. In the meantime, room-temperature lattice thermal conductivity is only 0.682 Wm -1 K -1 and exhibits strong strain dependence. The weakened anharmonic three-phonon scattering rate due to the tradeoff between the number and the strength of scattering channel largely compensates for the influence of the reduced phonon group velocity, causing a monotonous increase in the lattice thermal conductivity with the strain changing. Moreover, the lattice thermal conductivity can be reduced further by limiting the size of monolayer under tensile strain, due to the enhanced size dependence of the thermal conductivity.

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