• Pramanik, P.; Reehuis, M.; Tovar, M.; Hoser, A.; Hoffmann, J.U.; Chen, Y.S.; Lin, J.G.; Weise, B.; Waske, A.; Thota, S.: Strong correlation between structure and magnetic ordering in tetragonally distorted off-stoichiometric spinels Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4. Physical Review Materials 6 (2022), p. 034407/1-12

10.1103/physrevmaterials.6.034407
Open Access Version

Abstract:
We report a systematic study on the structural and magnetic properties of off-stoichiometric polycrystalline bulk spinels Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4 using neutron and x-ray diffraction, ferromagnetic resonance, and magnetic measurements. Both compounds show a weak tetragonal distortion with c/a<1, where the crystal structure could be refined in the tetragonal space group I41/amd. Both Co2+ and Cu2+ ions are located at the tetrahedral A site, and Mn3+ and Co3+ at the octahedral B site. Ferrimagnetic (FI) ordering of Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4 sets in below 184 and 164 K, respectively. Magnetic structure analysis revealed that the ferrimagnetically coupled A2+- and B3+-site moments are aligned parallel to the tetragonal c axis. Additionally, a noncollinear antiferromagnetic order appears in the ab plane, where the moments point along [110] and [1¯10]. The net magnetic moment [2μFI(MnB/CoB)−μFI(CoA)] of Mn1.15Co1.85O4 obtained from neutron data varies between 0.88–1.08 μB which is in good agreement with M=0.89–1.13 μB as determined from magnetization measurements. However, for the Cu-containing compound a larger discrepancy in the magnetic moment was observed between the neutron data (1.89–1.92 μB) and low-temperature (T=1.9 K) field-dependent (H=90 kOe) magnetization data (0.97–1.21 μB). From the three-sublattice model we obtained canting angles 28∘ and 25∘ for Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4, respectively. Both the bulk systems exhibit high magnetocrystalline anisotropy (KU∼9×105 and 7.5×105 erg/cm3) and a field-induced transition (HD) across 4.0 kOe due to the domain reorientation. Temperature (1.9–350 K) and field (±90 kOe) dependence of magnetization data confirms the high-spin (S=32 and S=2) ground-state configuration for both the divalent Co and trivalent Mn.