Charge carrier transport, spin frustration and relaxation in disordered La2−xCaxFeMnO6 double perovskites

Abstract

In this paper the influence of spin frustration on bulk magnetic properties and charge carrier conduction on bulk electrical transport in La2−xCaxFeMnO6 (LCFMO; where x = 0, 0.1, 0.2 or 0.5) compounds is comprehensively reported. The anti-site disorder of Fe and/or Mn sites is qualitatively determined by the Reitveld refinement of x-ray diffraction and magnetic properties. Mixed valence states (+3 and +4) of both Fe and Mn cations are determined by comprehensive analysis using x-ray photoelectron spectroscopy, which reveals a significant increment in Fe3+ concentration with increasing Ca2+ doping. The variation in resistivity with increasing temperature shows the semiconducting nature of all samples. The values of the saturation magnetic moment (MS ∼1.7 μB/f.u. for pure LFMO and ∼1.5 μB/f.u. for 25% Ca2+-doped LCFMO 25 sample) suggest that these samples exhibit a strong ferrimagnetic ground state at 5 K. Temperature-driven magnetization and AC susceptibility measurements reveal the existence of multiple spin cluster glassy states along with a Griffiths phase within the materials. Values of the characteristic frequency (∼105–107 Hz) and spin-flipping time (∼10−5–10−7 s) are obtained from both Vogel–Fulcher and power-law analyses. These analyses demonstrate that cluster glass (CG) regions exist at lower temperatures. Interestingly, Ca2+ doping leads to the development of new CG-like features at approximately 14 K and 195 K for 25% Ca2+ doping. These findings may provide useful insight for designing future spintronic materials that exhibit inhomogeneous spin frustration and tunable electronic states.