The solid lines represent the fitting curves assuming the log-normal function, where
on a non-background sample holder fixed to a cold head in a high-vacuum (<10−3 Torr), low-temperature (approximately 80 K) chamber. The CuO nanowire was excited by focusing a 514.5-nm Ar ion laser (Coherent Inc., Santa Clara, CA, USA) with a 5-mW laser power on the sample to form a spot size of approximately 1 μm in diameter, giving a power density of 102 W/cm2. From
the factor group analysis of the zone center modes for the monoclinic structure, given by Rousseau et al. , there are three Raman active modes (A g, B g 1, and B g 2) predicted in the spectra of CuO nanowires. Figure 2 shows an example of a series of Raman spectra taken at various temperatures, covering the antiferromagnetic transition temperature, with a mean diameter of 120 ± 8 nm. There are two phonon modes revealed in the Raman spectra taken of the CuO nanowires at T = 193 K at 300.2 and 348.8 cm−1, which are related to A g and B g 1 symmetries [19, 20]. The peak position is lower
than the value of the bulk CuO (A g = 301 cm−1 and B g 1 = 348 cm−1) , reflecting the size effect which Crenigacestat purchase acts to confine the lattice vibration in the radial directions resulting in a shift in the A g and B g 1 symmetries. As the temperature decreases to 83 K, it can be clearly seen that the peak positions of the A g and B g 1 modes around 301.8 and 350.9 cm−1, shown at the top of Figure 2, shifted toward higher Raman frequencies. While the temperature increased from 83 to 193 K, the peak position of the A g mode softened by 0.7%. Since the frequency of the phonon mode is related to Cu-O stretching, it is Leukocyte receptor tyrosine kinase expected that the frequency will downshift with increasing temperature, primarily due to the softening of the force constants that originate from the thermal expansion of the Cu-O bonds, resulting from the change in vibrational amplitude [22, 23]. In the study, the high resolution of our spectrometer allowed detection of relative change as small as 0.5 cm−1, and the vibrational frequency of a phonon mode can be used to determine the spin-phonon interaction. A phonon-phonon effect originates from the dynamical motion of lattice displacements, which are strongly coupled to the spin degrees of freedom dynamically below the magnetic ordering temperature. This coupling between the lattice and the spin degrees of freedom is named as spin-phonon.