Browsing by Author "Reuvekamp, Patrick Gerald"

Filter results by typing the first few letters
Now showing 1 - 1 of 1
  • Thumbnail Image
    ItemOpen Access
    Investigation into the magnetic and the structural properties of two low-dimensional antiferromagnets TiPO4 and CrOCl
    (2014) Reuvekamp, Patrick Gerald; Keimer, Bernhard (Prof. Dr.)
    Titanium (III) phosphate TiPO4 (3d1 electronic configuration with S = 1/2) is a one-dimensional quantum antiferromagnet exhibiting non-conventional spin-Peierls behaviour at low temperatures. Chromium oxychloride CrOCl (3d3 electronic configuration with S = 3/2) is a two-dimensional antiferromagnet consisting of ferromagnetic spin chains interconnected by competing anti and ferromagnetic spin exchanges interactions. The magnetic and the structural properties of these compounds are intimately related via magnetoelastic coupling. Incommensurate and commensurate phases are observed at low temperatures in both compounds. These systems are investigated using various experimental techniques, i.e. magnetic susceptibility, heat capacity, dielectric, Raman scattering and electron paramagnetic resonance measurements. The mangetoelastic coupling in these compounds is explored using a thermal expansion cell commissioned and tested in the course of this dissertation work. TiPO4 consists of quasi one-dimensional Ti3+ spin S = 1/2 chains running along the c-axis with strong antiferromagnetic intrachain coupling (Jintra =-965 K, Jinter= -20 K). A two-stage spin-Peierls transition occurs in TiPO4 consisting of two successive phase transitions at Tc1 = ~74 K and Tc2 = ~110 K. The temperature dependence of the lattice parameters as well as the magnetic field and the pressure dependence of the two phase transitions are studied extensively. The results are analyzed and discussed in terms of the spin-Peierls theory and the crystallographic data. CrOCl is characterized by an intricate two-dimensional intrachain and interchain spin exchange scenario. A low temperature monoclinic distortion occurs at the onset of the commensurate antiferromangetic order at TN = ~13.5 K. The commensurate phase is preceded by an incommensurate antiferromagnetic phase starting below 27 K. Ferromagnetic spin exchange interactions are dominant in contrast to the low temperature antiferromagnetic ordering. In low temperature regime (T < 30 K), various measurement techniques are employed to construct extended (H, T) magnetic phase diagrams for H par c and H per c. The phase diagrams are very complex resulting from the magnetic frustration of the competing spin exchange interactions. The spin exchange interactions are investigated by employing spin polarized density functional theory calculations and classical mean-field/Monte Carlo simulations. Using the density functional theory results, the extended (H, T) magnetic phase diagrams are discussed in terms of the ANNNI model.