Magnetic excitations and anomalous spin-wave broadening in multiferroic FeV2O4

Abstract

We report on the different roles of two orbital-active Fe2+ at the A site and V3+ at the B site in the magnetic excitations and on the anomalous spin-wave broadening in FeV2O4. FeV2O4 exhibits three structural transitions and successive paramagnetic (PM)-collinear ferrimagnetic (CFI)-noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM-orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbitcoupling-induced anisotropy at the Fe2+ site. While there is no measurable increase in the energy gap from the orbital ordering of V3+ at the orthorhombic/CFI-tetragonal/NCFI transition, anomalous spin-wave broadening is observed in the orthorhombic/CFI state due to V3+ spin fluctuations at the B site. The spinwave broadening is also observed at the zone boundary without softening in the NCFI/ferroelectric phase, which is discussed in terms of magnon-phonon coupling. Our study also indicates that the Fe2+ spins without the frustration at the A site may not play an important role in inducing ferroelectricity in the tetragonal/NCFI phase of FeV2O4. We report on the different roles of two orbital-active Fe 2+ at the A site and V 3+ at the B site in the magnetic excitations and on the anomalous spin-wave broadening in FeV 2 O 4 . FeV 2 O 4 exhibits three structural transitions and successive paramagnetic (PM)-collinear ferrimagnetic (CFI)-noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM-orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbit-coupling-induced anisotropy at the Fe 2+ site. While there is no measurable increase in the energy gap from the orbital ordering of V 3+ at the orthorhombic/CFI-tetragonal/NCFI transition, anomalous spin-wave broadening is observed in the orthorhombic/CFI state due to V 3+ spin fluctuations at the B site. The spin-wave broadening is also observed at the zone boundary without softening in the NCFI/ferroelectric phase, which is discussed in terms of magnon-phonon coupling. Our study also indicates that the Fe 2+ spins without the frustration at the A site may not play an important role in inducing ferroelectricity in the tetragonal/NCFI phase of FeV 2 O 4 .

Orthorhombic distortion and orbital order in the vanadium spinelFeV2O4

“…In contrast, the peak splitting at other temperatures is similar to that in past studies [12]. In the NPD study, signs of these transitions were also observed, consistent with recent literature [13,20,21]. However, the peak splitting was not observed as clearly as in the SPD study because of the lower angular resolution of NPD.…”

“…However, the OO models of V 3+ ions at T N2 , suggested by Nii et al [11] and Kang et al [18], are contradictory. Additionally, the origins and structural properties of the low-temperature phase including the elongated tetragonal phases [12] are still disputed despite numerous experimental and theoretical efforts [11][12][13][14][15][16][17][18][19][20][21]. In this paper, we tackle the accurate structure analysis with high-resolution synchrotron diffraction and neutron diffraction by using polycrystalline samples as well as single crystals of FeV 2 O 4 and orbitally diluted materials for each A and B site.…”

Magnetic and Magnetodielectric Properties of Epitaxial Iron Vanadate Thin Films

“…[9] For the particular case of FeV2O4 (stoichiometric FVO), it possesses unique properties on account of the interaction of the two cations through their oxygen octahedral network (Fe 2+ and V 3+ on the tetrahedral and octahedral sites, respectively) that controls this interplay among spin, orbital, and lattice degrees of freedom. [2][3]10] For instance, the magnetoelectric and ferroelectric properties of polycrystalline FeV2O4 (and related chemical formulations) have been reported. Takei et al [11] found that the capacitance of polycrystalline FeV2O4 exhibits a magnetic This article is protected by copyright.…”

Do electron distributions with orbital degree of freedom exhibit anisotropy?

“…In this system, despite the lack of charge degrees of freedom due to the Mott insulator, both electronic correlations and geometric frustration are present, resulting in an interplay between the different degrees of freedom, such as spin, orbital, and lattice, which leads to three successive phase transitions with decreasing temperature. [15][16][17][18][19][20][21][22][23][24] FeV 2 O 4 has been widely studied from both experimental and theoretical perspectives; however, owing to the intertwining of the multiple degrees of freedom, it is difficult to understand the orbital state completely. AV 2 O 4 with other cations at the Fe site has been studied to avoid multiple degrees of freedom.…”