Periodicity of the Spin Structure Observed in the Optical Response of CeBi Single Crystals

Abstract

We report a study of the optical conductivity of CeBi in different magnetic phases. Going from the paramagnetic phase to the various antiferromagnetic and ferrimagnetic phases, different new interband transitions appear below the absorption edge of the p ! d transitions. These new interband transitions disappear in a magnetic field that is sufficiently strong to align the spins parallel. The appearance of new interband transitions is indubitably associated with the folding of the Brillouin zone, which is a consequence of the change of the periodicity of the spin structure. [S0031-9007(96)00072-5] PACS numbers: 78.20.Ci, 75.25.+z, 75.50.Ee, 75.50.Gg During the last two and a half decades, cerium monopnictides have attracted much interest due to their numerous striking properties. Besides the intensively discussed question of the two photoemission peaks with f character [1], we would like to cite here the reduction of the crystal field splitting of the 4f 1 state compared to the point charge model [2], the Kondo behavior of the resistivity [3], giant magneto-optical Kerr signals in CeSb [4,5], and the very complex magnetic phase diagram in the heavier cerium pnictides [6]. The cerium monopnictides crystallize in the rock-salt structure, and they are semimetals. Systematic magnetization and neutron scattering investigations revealed nine magnetic phases in CeBi [6]. In zero magnetic field CeBi undergoes at 25.2 K a secondorder phase transition to an antiferromagnetic phase with a type I structure ͑1 2 12͒. At 13 K CeBi shows a firstorder phase transition to a type IA phase with the periodicity 1 1 22. In a magnetic field applied along [001], several ferrimagnetic structures appear. The main phase is a ferrimagnetic phase with (001) planes stacked in the sequence 1 1 12. At low temperatures a transition to a spin-aligned phase occurs at 4.7 T [6].First, optical reflectivity measurements on CeSb were reported by Schoenes and Reim [7] and Reim et al. [4]. These room temperature measurements gave evidence for one interband transition in CeSb at 0.4 eV, which was attributed to an f ! d transition. Later Kwon et al. [8] reported reflectivity measurements for CeSb and CeBi, including low temperature data. The latter showed the appearance of two structures in the infrared optical conductivity, but the origin of these features could not be definitely clarified. In this Letter, we report a detailed study of the infrared properties of CeBi as a function of temperature and magnetic field. The variation of these two external parameters allowed us to switch between several magnetic phases of CeBi and to observe the corresponding variations in the infrared optical conductivity. The optical response of CeBi reacted distinctly according to all changes of the periodicity of the magnetic structure. This is, to our knowledge, the first direct observation of the relation between the periodicity of the spin structure and the optical conductivity of a material in two antiferromagnetic phases, as well as in a ferrimagnetic phase and in ...

NEW KERR RECORD: 90° SINGLE KERR ROTATION IN CeSb

“…the formation of magnetic superstructures leads to a folding of the valence and conduction bands and as a consequence to new interband transitions. Similar effects have also been observed recently in CeBi [6]. Because the latter material has a somewhat less complex magnetic phase 4 diagram with simpler antiferrornagnetic and ferrimagnetic phases a full schematic interpretation of the changes in the optical conductivity could be performed.…”

Experimental and theoretical investigation of optical properties of dysprosium monopnictides

“…1,5 CeAs, CeSb, and CeBi were reported to display an unusually large magnetooptical Kerr rotation. 3,4 Optical spectroscopy could prove that GdP is metallic, with a small number of free carriers derived from the Drude-type conductivity. 6 Similar metalliclike optical spectra were subsequently reported for a number of other rare-earth monopnictides, such as, e.g., LaSb, CeSb, PrSb, YbAs, and CeBi.…”

Change of Electronic Structure Induced by Magnetic Transitions in CeBi

“…4,5 Pittini and coworkers pointed out that the electronic band structure is folded by the spin structure in the AF-1 phase. 10 As previously mentioned, the change in the σ(ω) spectrum can be explained by the band folding. However, the change in the σ(ω) spectrum between 11 and 25 K has never been previously observed.…”

“…9 Pittini and coworkers have indicated that the folding of the band structure of CeBi by the spin structure can be observed in the σ(ω) spectra. 10 Here, the spin moments originating from the Ce 4f 1 Γ 8 and σ(ω) spectra reflect the Bi 6p and Ce 5d band structure. The coupling between the Ce 4f 1 Γ 8 spin moment and the band structure is due to pf mixing.…”