First-principles investigation of electronic structure,effective carrier masses, and optical properties of ferromagnetic semiconductor CdCr_2S_4

The electronic structures, the effective masses, and optical properties of spinel CdCr_2S_4 are studied by using the fullpotential linearized augmented planewave method and a modified Becke–Johnson exchange functional within the densityfunctional theory. Most importantly, the effects of the spin–orbit coupling（SOC） on the electronic structures and carrier effective masses are investigated. The calculated band structure shows a direct band gap. The electronic effective mass and the hole effective mass are analytically determined by reproducing the calculated band structures near the BZ center.SOC substantially changes the valence band top and the hole effective masses. In addition, we calculated the corresponding optical properties of the spinel structure CdCr_2S_4. These should be useful to deeply understand spinel CdCr_2S_4 as a ferromagnetic semiconductor for possible semiconductor spintronic applications.

Theoretical Study of the Multiferroic Behavior of the Magnetic Relaxor Ferroelectric CdCr₂S₄

Using a microscopic model and the replica method as well as the Green’s function theory, we have investigated the relaxor and multiferroic behavior of CdCr2S4. The magnetization, the remanent polarization Pr and the real part of the dielectric function are studied theoretically as a function of temperature, with and without a magnetic field, respectively. The magnetization and the polarization exist together below the magnetic phase transition temperature. Pr decreases whereas increases and the peak shifts to smaller temperature values with increasing magnetic field h. Moreover, the temperature and electric field E dependence of the magnetization M is also discussed. A kink is observed around the ferroelectric transition temperature. The kink is deeper for stronger electric fields and anharmonic spin-phonon interactions.