Structural and magnetic properties of LiMn1.5Fe0.5O4 spinel oxide

Geometrical frustration, which arises from the topology of a well-ordered structure rather than from disorder, has recently become a renewed interest. In particular, geometrical frustration among spins in the spinel oxides can lead to exotic low-temperature states. We reported a joint experimental and theoretical investigation of Fe-doping effect on LiMn2O4 spinel oxide in which magnetic moments have geometrical frustration. The structural and physical properties of LiMn1.5Fe0.5O4 were studied by means of Moessbauer spectroscopy, X-ray diffraction, scanning electron microscope (SEM), electrical and magnetic measurements. Electronic conductivity measurements showed that Verwey-type transition is absent in heavily Fe-doped LiMn2O4. In addition, LiMn1.5Fe0.5O4 exhibits a semiconductor characteristic in resistivity with an energy gap Eg=0.27 eV, which is consistent with our first-principle simulation. A large resistivity at room temperature for LiMn1.5Fe0.5O4 indicates low concentration of conduction electrons corresponding to electronic localization behavior. X-ray diffraction refinement as well as Moessbauer analysis suggests that Fe ions preferentially substitute for Mn ions on the octahedral B-sites. Moreover, small amount of Fe replace for Li ions to form a site inversion in spinel structure. In contrast to the pure and low-Fe-doped LiMn2O4 samples, LiMn1.5Fe0.5O4 has an antiferromagnetic transition at TN=34 K. The Fe dopants enhance the antiferromagnetic interaction among moments accompanied by breaking the original moment equilibrium and suppressing the magnetic frustration in LiMn2O4.