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Switching of Dominant Magnetic Exchange Interactions Between Tetrahedral-octahedral and Octahedral-octahedral Sites in (Mn<>1-xCrx)3O4 Spinels
G. D. Dwivedi, Tsung-Wen Yen, S. M. Kumawat, C. W. Wang, D. Chandrasekhar Kakarla, A. Tiwari, H. D. Yang, S. M. Huang, C. M. Chung, S. J. Sun, H. Chou
2023/12/31
Magnetic exchange interactions in Mn3O4 spinel systems are complicated due to the presence of magnetic frustration between one tetrahedral and two octahedral sites, and the strongly correlated Jahn–Teller crystal distortion due to the singly occupied eg band of Mn3+ cations at the octahedral site. In general, the tetrahedral–octahedral exchange interaction is the most dominant interaction among the other two interactions which enforces the octahedral and tetrahedral spins to align parallel to themselves. Doping of Cr3+ ions (with the empty eg band) at the octahedral sites of Mn3O4 reduces the Jahn–Teller distortion and the magnetic moment in the system and hence it affects the magnetic anisotropy, magnetic exchange interaction, and magnetic frustration. In this manuscript, we have investigated the variations in these properties of the Mn2.7Cr0.3O4 and Mn1.5Cr1.5O4 systems and compared them to those of the documented parent Mn3O4 to unveil the evolution of these cross interactions. The neutron diffraction results disclose the noncollinear magnetic structure of Mn2.7Cr0.3O4, while Mn1.5Cr1.5O4 shows a collinear magnetic structure [G. D. Dwivedi, C. W. Wang, S. M. Kumawat and H. Chou, Appl. Phys. Lett., 2020, 116, 182406]. A comparative study of the magnetic structure and exchange interactions (calculated using the TB2J method) of the low doping Mn2.7Cr0.3O4 reveals that the exchange interaction between the nearest octahedral–octahedral cations is the most prominent due to the ionic size effect, which is contrary to the general understanding of spinel systems. However, the exchange interactions in the high doping cubic Mn1.5Cr1.5O4 switched back to the dominant AFM interaction between tetrahedral–octahedral ions due to the smaller moment of Cr ions.