Polyhedral distortions and unusual magnetic order in spinel FeMn${}_2$O${}_4$

Abstract

Spinel compounds AB${}_2$X${}_4$ consist of both tetrahedral (AX${}_4$) and octahedral (BX${}_6$) environments with the former forming a diamond lattice and the latter a geometrically frustrated pyrochlore lattice. Exploring the fascinating properties and their correlations with structural features is critical in understanding these materials. FeMn${}_2$O${}_4$ has been reported to exhibit one structural transition and two successive magnetic transitions. Here, we report the polyhedral distortions and their correlations to the structural and two magnetic transitions in FeMn${}_2$O${}_4$ by employing the high-resolution neutron powder diffraction. While a large trigonal distortion is found even in the high-temperature cubic phase, the first-order cubic-tetragonal structural transition associated with the elongation of both tetrahedra and octahedra along the $c$ axis occurs at $T_S\approx$ 750 K, driven by the Jahn-Teller effect of the orbital active B-site Mn${}^{3+}$ cation. A strong magnetoelastic coupling is unveiled at $T_{N1}\approx 400$ K as manifested by the appearance of Nèel-type collinear ferrimagnetic order, an anomaly in both tetrahedral and octahedral distortions, as well as an anomalous decrease of the lattice constant $c$ and a weak anomaly of $a$. Upon cooling below $T_{N2}\approx 65$ K, it evolves to a noncollinear ferrimagnetic order with a canting of half B-site $M{n}^{3+}$/$F{e}^{3+}$ spins in the pyrochlore lattice, which is a unique magnetic order among spinels. Such a noncollinear order induces modifications of the O-B-O bond angles in the octahedra without affecting much the bond lengths of the tetrahedra/octahedra. Our study indicates that FeMn${}_2$O${}_4$ is a wonderful platform to unveil interesting magnetic order and to investigate their correlations to polyhedral distortions and lattice.

13 pages, 10 figures, Accepted for publication in Chemistry of Materials

References in corpus (7)

• Spin current and magneto-electric effect in non-collinear magnets
• Magnetic and orbital ordering in the spinel MnV2O4
• Spin and Orbital Order of the Vanadium Spinel MgV2O4
• Orbital order in ZnV${}_2$O${}_4$
• Magnetic order and ice rules in the multiferroic spinel FeV2O4
• CdV2O4: A rare example of a collinear multiferroic spinel
• Hidden local symmetry breaking in a kagome-lattice magnetic Weyl semimetal

Cited by in corpus (4)

• Room Temperature Ferrimagnetism, Magnetodielectric and Exchange Bias Effect in CoFeRhO${}_4$
• Multiferroicity in the Presence of Exchange Bias: The Case of Spinel CoMn2O4
• Anisotropic Band-Split Magnetism in Magnetostrictive CoFe${}_2$O${}_4$
• Intrinsic Topological Weyl Phase Transition Induced by a Magnetostructural Transformation in a Kagome Magnet