Anisotropic phonon and magnon vibration and gate-tunable optoelectronic properties of nickel thiophosphite


 Transition metal phosphorus trichalcogenides retain spin-charge coupling and lattice vibrations in different layers, which are useful for spintronic and optoelectronic devices. The phonon, magnons and excitonic properties of 2D ternary nickel-phosphorus trisulfides (NiPS3) are investigated using Raman spectroscopy and photoluminescence (PL) study. With magnetic exchange interaction, an exotic phonon scattering degenerates the optical phonons into in-plane Ag and Bg modes. We have observed eight Raman modes with two acoustic anisotropic magnon modes (M1, M2) below the critical temperature for co-(XX), while only M1 at cross (XY) polarizations. The M1 mode is coupled with phonon Bg mode that can survive after transition temperature. The phonon and magnon modes soften with temperature variation, which is attributed to anharmonic phonon-phonon coupling and interlayer forces. The polarized Raman shows the 2-fold and 4-fold symmetry orientation of phonon and magnon modes, respectively, which exhibits strong in-plane anisotropic phonon/magnon. The PL spectra revealed the existence of bound excitonic features and ensemble emitters in NiPS3. The robust interlayer excitation and structural stability further revealed the optothermal properties. Moreover, the fabricated field-effect transistor (FET) on NiPS3 reveals p-type semiconducting nature with an ON/OFF ratio~5×106 and mobility of~16.34 cm2V−1s−1, while the rectification ratio indicates their diode characteristics. Similarly, the photocurrent is enhanced by changing the wavelength of light, which shows the potential for optoelectronics. The strong spin-charge interaction provides new insights into these materials' magneto-optical and thermal properties for memory devices.