Magnetism of LiMn2O4 manganite in structurally ordered and disordered states

The specific features of the crystal structure and the magnetic state of stoichiometric lithium manganite in the structurally ordered Li[Mn 2 ]O 4 and disordered Li 1 − δ Mn δ [Mn 2 − δ Li δ ]O 4 (δ = 1/6) states have been investigated using neutron diffraction, X-ray diffraction, and magnetic methods. The structurally disordered state of the manganite was achieved under irradiation by fast neutrons ( E eff ≥ 1 MeV) with a fluence of 2 × 10 20 cm −2 at a temperature of 340 K. It has been demonstrated that, in the initial sample, the charge ordering of manganese ions of different valences arises at room temperature, which is accompanied by orthorhombic distortions of the cubic spinel structure, and the long-range antiferromagnetic order with the wave vector k = 2π/ c (0, 0, 0.44) is observed at low temperatures. It has been established that the structural disordering leads to radical changes in the structural and magnetic states of the LiMn 2 O 4 manganite. The charge ordering is destroyed, and the structure retains the cubic symmetry even at a temperature of 5 K. The antiferromagnetic type of ordering transforms into ferrimagnetic ordering with local spin deviations in the octahedral sublattice due to the appearance of intersublattice exchange interactions.