Magnetic structure of mixed iron-gallium borate crystals: EMR and SQUID studies

Abstract

Iron-gallium borate, FexGa1−xBO3, single crystals have been synthesized by the solution in the melt technique. The exact x-values in the crystals have been determined by X-ray fluorescence analysis and checked by Energy Dispersive X-Ray Spectroscopy. Scanning Electron Microscopy has been used to map distributions of iron and gallium ions in the crystals. The electron magnetic resonance (EMR) spectra as well as field and temperature dependences of the magnetization obtained by SQUID reveal the existence of different magnetic phases in different x ranges, viz. weakly ferromagnetic antiferromagnetic, magnetic cluster and paramagnetic phase. For crystals with 0.32 ≤ x ≤ 0.83, the Néel temperatures, TN, have been determined. The magnetometry of these crystals suggests the existence of another magnetic transition at a temperature well below TN, tentatively ascribed to a Morin type transition. Detailed EMR and SQUID studies of the crystal with x ≈ 0.2 reveal the existence of magnetic nanoclusters showing superparamagnetic behaviour. Using a laboratory developed code based on the Monte-Carlo technique, spatial distributions of dia- and paramagnetic ions in the crystal with x ≈ 0.2 has been visualized and possible cluster sizes have been estimated.