Spin phonon coupling in rod-shaped half-metallic CrO₂ultrafine particles: a magnetic Raman scattering study

Abstract

Half-metallic CrO 2 powder compact with rod-shaped nanoparticles was studied by micro-Raman scattering in the presence of an external magnetic field at room temperature (300 K). In the low-field region (H 250 mT), the frequency and intensity of the E g mode, an internal phonon mode of CrO 2 , increase dramatically with increase in the magnetic field, while the corresponding linewidth decreases. The above parameters become constant when the CrO 2 powder enters the saturation state at higher magnetic field. The pronounced anomalies of the Raman phonon parameters under a low magnetic field are attributed to the spin-phonon coupling enhanced by the magnetic ordering, which is induced by the external magnetic field.

Raman and infrared-active phonons in hexagonal HoMnO3single crystals: magnetic ordering effects

“…4, its frequency deviates from the dependence expected for the anharmonic decay and hardens by as much as 5 cm −1 between T N and 10 K. According to the lattice dynamics calculations (Table I) this phonon corresponds to the rotations of the MnO 5 structural units in the xyplane and effectively modulates Mn-O-Mn exchange interaction. Similar phonon frequency anomalies at the magnetic ordering temperature have been observed earlier in CuO [15], SrRuO 3 [16], and CrO 2 [17,18].…”

Pressure-induced phonon softenings and the structural and magnetic transitions in CrO2

“…Especially, there is no experimental or theoretical report on the phonon dispersion curve for CrO 2 , except for a few Raman studies. [4][5][6] Under the pressure, CrO 2 is known to undergo the structural transition from the ground state tetragonal CrO 2 (t-CrO 2 ) to the orthorhombic CrO 2 (o-CrO 2 ) of CaCl 2 -type at P = 12-14 Gpa. 4,7 The question followed is whether there will an additional structural transitions from o-CrO 2 at higher pressure.…”

Spin-induced variations of phonon frequencies in ferromagnetic metals

“…The first thing to note is that the frequency shows an explicit appreciable dependence on the magnetic moment, and that jdn m ðqÞjp15 cm À1 . This can be compared with the observed frequency change in the above mentioned experiments on SrRuO 3 and CrO 2 , in which the frequency changes were found to be less than 10 cm À1 as the sample magnetization changes [5,7].…”

“…Yu et al [7] observed through Raman scattering experiments that the frequency of the E g phonon mode of CrO 2 dramatically increases in an external magnetic field. Although the spin-phonon coupling was considered as the origin of the frequency increase, no quantitative analysis was presented.…”