Optical and magneto‐optical study of the magnetic properties of RbFeCl3, RbFeBr3, and disordered materials of intermediate composition

摘要

In magnetically disordered materials, disorder is usually obtained by dilution with nonmagnetic ions. We present here a prospective work on single crystals of RbFeCl3-xBrx (x = 0/0.04/0.2/1/2/3), where magnetic disorder is expected to be induced via the ligands by eventually changing at random the superexchange between Fe2+ ions. We have measured the optical, Raman, and magnetic circular dichroism (MCD) spectra of our crystals. We focus here on the dependence of absorption versus temperature and ligand, with emphasis on the magnetic properties of the chains. For RbFeCl3 and RbFeBr3, the temperature dependence of the absorption follows the general trends predicted by Tanabe et al.; however spin‐orbit coupling is shown to restore significant absorption intensity at TN for RbFeCl3. Mixed compounds exhibit a structural disorder as demonstrated by our Raman and optical experiments. Moreover, relying on the absorption data, we conclude that for x = 0.04, 0.2, and 1, the intrachain interaction is not essentially modified, whereas for x = 2 we suggest that magnetic disorder does exist. Finally, our MCD results are briefly mentioned, and their significance is discussed in terms of the magnetic properties of the pure compounds.