There has been considerable recent interest in the design of diluted magnetic semiconductors, with a particular focus on the exploration of different semiconductor hosts. Among these, the oxide-based diluted magnetic semiconductors are attracting increasing attention, following reports of room temperature ferromagnetism in anatase TiO2 and wurtzite ZnO doped with a range of transition metal ions. In this review we summarize the current status of oxide-based diluted magnetic semiconductors, and discuss the influence of growth method, substrate choice, and temperature on the microstructure and subsequent magnetic properties of thin films. We outline the experimental conditions that promote large magnetization and high ferromagnetic Curie temperature. Finally, we review the proposed mechanisms for the experimentally observed ferromagnetism and compare the predictions to the range of available data.

https://iopscience.iop.org/article/10.1088/0953-8984/17/27/R01/pdf

Transition metal-doped TiO2 and ZnO?present status of the field

Lattice vibration spectra. LIX. Single crystal infrared and Raman studies of spinel type oxides

Coherent magnons and phonons are excited by subpicosecond laser pulses in the weak ferromagnet ${\text{FeBO}}_{3}$. Impulsive stimulated Raman scattering (ISRS) is proven to be the microscopic mechanism of the excitation. It is shown that coherent magnons can be excited by both linearly and circularly polarized laser pulses where the efficiency of the process depends on the mutual orientation of the magnetic and crystallographic axes and the light propagation direction. The strong ellipticity of the ferromagnetic magnon mode is demonstrated, both experimentally and theoretically, to be essential for the excitation and observation of such coherent magnons. Because of this ellipticity, the amplitude of the coherent magnons excited by linearly polarized light may exceed by 2 orders of magnitude the amplitude of those excited by circularly polarized light. The primary difference between the excitation of coherent magnons by linearly polarized pulses via ISRS and via the earlier reported process of photoinduced magnetic anisotropy is discussed. Furthermore, the ISRS process is found to be responsible for the excitation of two optical phonon branches (8.4 and 12.1 THz) observed in our experiments. A coherent excitation, with a temperature-independent frequency of 0.7 THz, has also been observed in the magnetically ordered phase but could not be assigned to any optical phonon modes known in ${\text{FeBO}}_{3}$. The well-pronounced dependence of the amplitude of this mode on temperature suggests that this mode of nonmagnetic origin becomes Raman active only in the magnetically ordered phase and, therefore, can be excited and observed only below the N\'eel temperature.

/pdf/impulsive-excitation-of-coherent-magnons-and-phonons-by-4b8wcr3fgi.pdf

Impulsive excitation of coherent magnons and phonons by subpicosecond laser pulses in the weak ferromagnet FeBO3

Magnetic correlations influence the energy of conduction electrons through the exchange coupling. A magnetization leads to a splitting of the band where, however, the states of the higher band are unstable against spin‐flip with spin‐wave production. The rather unknown ion‐position dependence of the spin Hamiltonian couples the spins to the phonons. For weak spin‐spin couplings an adiabatic principle is assumed. The effect of spin order on the phonon frequency, on the infrared and Raman spectra, and the isotope effect of magnetic couplings is discussed.

Influence of Magnetic Order on Conduction Electrons and Phonons in Magnetic Semiconductors

Influence of magnetic ordering on the phonon Raman spectra in YCrO3 and GdCrO3

Measurements are reported of the Raman effect on single crystal ferromagnetic CdCr2Se4 and CdCr2S4 as a function of temperature. The lines observed at 158 cm−1, 172 cm−1 and 241 cm−1 for CdCr2Se4 and 257 cm−1, 281 cm−1 and 396 cm−1 for CdCr2S4 have been identified as due toГ12+,Г25+ andГ1+ phonons, respectively. Certain lines ofГ1+ orГ25+ symmetry, observed in both materials, show a temperature dependence of the intensity which resembles the behaviour of the spin correlation function. Some of these lines also exhibit a symmetry change at the Curie point. A group theoretical analysis of the eigenvectors of the Raman active modes is given. The results are interpreted in terms of a model proposed by Baltensperger which involves the ion position dependence of the magnetic exchange interaction in order to couple spin system and phonons. The weak frequency shift of the lines, which occurs predominantly in the ordered state, is interpreted in terms of the same model.

Günther Harbeke

Papers

Phonons and magnetic order in ferromagnetic CdCr2Se4 and CdCr2S4

Raman scattering in ferromagnetic CdCr2Se4

Semiconductor device and process for the manufacture of the construction element