Temperature and field dependent Raman Studies on Cupric Oxide Single Crystals

Cupric oxide is a well known oxide material which shows two successive magnetic transitions at 230 K (T_N2) and 213 K (T_N1). Interestingly, it has been reported in recent times that a small electric polarization of 160 μC/m² develops along the b axis between 213-230 K. The origin of the observed macroscopic polarization is attributed to the noncollinear arrangement of spins and breaking of inversion symmetry via the Dzyaloshinskii-Moriya interaction.This mechanism is rather unusual and was suggested that spin-lattice coupling plays a crucial role. In the current work, we present temperature dependent Raman measurements on single crystalline CuO in presence of a magnetic field. Room temperature Raman measurements reveal three prominent Raman modes at 302 cm^-1, 350 cm^-1 and 635 cm^-1 consistent with earlier reports. Interestingly, we find a new mode appearing at 240 cm^-1 below 175 K. This mode splits into two modes on an application of a small magnetic field. Our experiments suggests that the mode observed at 240 cm^-1 is a combination of a magnon mode and a zone folded phonon contrary to the earlier reports.