Experimental and theoretical interpretation of magnetic ground state of FeMnO3

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Magnetic structure of FeMnO3 has been studied using temperature dependent neutron diffraction measurements. The compound exhibits ferrimagnetic structure at room temperature and undergoes another long range antiferromagnetic order below 36 K. The evolution of the magnetic structure is tracked as a function of temperature and compared with the physical property measurements such as magnetization and dielectric constants. Mössbauer spectroscopy measurements at selected temperatures and different magnetic fields exhibit strong influence of the magnetic field on the hyperfine splitting in the magnetically ordered state. Neutron diffraction experiments used for studying the magnetic structure also reveals the presence of a strong magnetically disordered phase in addition to the long range ferrimagnetic phase, leading to magnetic anisotropy in the system. Theoretical calculations were carried out to study ordered and disordered FeMnO3 models by means of Density Functional Theory using PBE0 hybrid functional. The magnetic structure resolved from the refinement of neutron diffraction data is in good agreement with the theoretical model for FeMnO3 model, and the values obtained from the magnetization measurements are in good agreement with the theoretically calculated and experimentally refined magnetic structural model. Dielectric measurements on FeMnO3 exhibits phase transition at two temperatures, firstly around 36 K coinciding with the magnetic ordering temperature, and another around 100 K. The influence of magnetic field does not change these temperatures much, but there is slight change in the dielectric response under the applied magnetic field, which can be attributed to the change in magnetodielectric effect from positive to negative with increase in the temperature. The magnetodielectric study shows the presence of positive and negative magnetodielectric values in this system where the cross over takes placed around the magnetic ordering temperature. From a combined look at the theoretical and experimental work, it can be said that FeMnO3 exhibits complex magnetism with interesting, but tunable physical properties.