Abstract-High-temperature terahertz optical diode effect without magnetic order in polar FeZnMo3O8

Shukai Yu, Bin Gao, Jae Wook Kim, Sang-Wook Cheong, Michael K. L. Man, Julien Madeo, Keshav M. Dani, and Diyar Talbayev

https://journals.aps.org/prl/accepted/5207aY9eU001d860a35917591d77d6fd5ec933d8a

We present a terahertz spectroscopic study of polar ferrimagnet FeZnMo3O8. Our main finding is a giant high-temperature optical diode effect, or nonreciprocal directional dichroism, where the transmitted light intensity in one direction is over 100 times lower than intensity transmitted in the opposite direction. The effect takes place in the paramagnetic phase with no long-range magnetic order in the crystal, which contrasts sharply with all existing reports of the terahertz optical diode effect in other magnetoelectric materials, where the long-range magnetic ordering is a necessary prerequisite. In \fzmo, the effect occurs resonantly with a strong magnetic dipole active transition centered at 1.27 THz and assigned as electron spin resonance between the eigenstates of the single-ion anisotropy Hamiltonian. We propose that the optical diode effect in paramagnetic FeZnMo3O8 is driven by signle-ion terms in magnetoelectric free energy.

Abstract-Terahertz-frequency magnetodielectric effect in Ni-doped CaBaCo4O7

Shukai Yu, C. Dhanasekhar, Venimadhav Adyam, Skylar Deckoff-Jones, Michael K. L. Man, Julien Madeo, E. Laine Wong, Takaaki Harada, Bala M. K. Mariserla, Keshav M. Dani, and Diyar Talbayev


https://journals.aps.org/prb/accepted/72074O5dR991bd3a430230a86e2aeb528788ab341

We present a study of terahertz frequency magnetoelectric effect in ferrimagnetic pyroelectric \cbco and its Ni-doped variants. The terahertz absorption spectrum of these materials consists of spin excitations and low-frequency infrared-active phonons. We studied the magnetic-field-induced changes in the terahertz refractive index and absorption in magnetic fields up to 17 T. We find that the magnetic field modulates the strength of infrared-active optical phonons near 1.2 and 1.6 THz. We use the Lorentz model of the dielectric function to analyze the measured magnetic-field dependence of the refractive index and absorption. We propose that most of the magnetoelectric effect is contributed by the optical phonons near 1.6 THz and higher-frequency resonances. Our experimental results can be used to construct and validate more detailed theoretical descriptions of magnetoelectricity in CaBaCo4-xNixO7.

Abstract-Terahertz frequency magnetoelectric effect in Ni doped CaBaCo4O7

Shukai Yu, C. Dhanasekhar, Venimadhav Adyam, Skylar Deckoff-Jones, Michael K.L. Man, Julien Madeo, E. Laine Wong, Takaaki Harada, Bala M.K. Mariserla, Keshav M. Dani, Diyar Talbayev

(Submitted on 14 Aug 2017)

https://arxiv.org/abs/1708.04345

We present a study of terahertz frequency magnetoelectric effect in ferrimagnetic pyroelectric CaBaCo4O7 and its Ni-doped variants. The terahertz absorption spectrum of these materials consists of spin excitations and low-frequency infrared-active phonons. We studied the magnetic-field-induced changes in the terahertz refractive index and absorption in magnetic fields up to 17 T. We find that the magnetic field modulates the strength of infrared-active optical phonons near 1.2 and 1.6 THz. We use the Lorentz model of the dielectric function to analyze the measured magnetic-field dependence of the refractive index and absorption. We propose that most of the magnetoelectric effect is contributed by the optical phonons near 1.6 THz and higher-frequency resonances. Our experimental results can be used to construct and validate more detailed theoretical descriptions of magnetoelectricity in CaBaCo4−xNixO7.