Investigation of magnetic materials with millimeter wave and Fourier transform spectroscopy

• Published in: Infrared physics 1991, Vol.32, p.91-103
• Main Authors: Geick, R., Greb, H., Hock, B., Jaitner, H., Maier, D., Pabst, T., Treutmann, W., Hosoya, S.
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Fundamental areas of phenomenology (including applications); Lasers; Optics; Physics
• ISSN: 0020-0891
• DOI: 10.1016/0020-0891(91)90100-T

We have studied the collective magnetic excitations of solids by optical methods, i.e. by magnetic resonance in the millimeter wave range and by Fourier transform spectroscopy in the far infrared. We have employed as source tunable backward wave oscillators, in addition to IMPATT sources, and have performed magnetic resonance experiments either by sweeping the magnetic field at fixed frequency or by sweeping the frequency at fixed magnetic field. Further, the samples have been studied in various configurations in order to obtain information not only about the energy of the collective excitation but also about the preferred spin direction in the long-range magnetic order. The performance of our experimental equipment is demonstrated by experimental results on Rb 2MnCl 4, Co 2SiO 4 and Fe 2SiO 4. Rb 2MnCl 4, is a quasi-two-dimensional antiferromagnet with tetragonal symmetry in the paramagnetic phase. A splitting of the zero-field antiferromagnetic resonance is ascribed to an orthorhombic distortion below T N. The silicates Co 2SiO 4 and Fe 2SiO 4 have an orthorhombic crystal structure with four formula units per unit cell and there are eight magnetic modes of different symmetry.