Magnetic-order induced phonon splitting in MnO from far-infrared spectroscopy

Rudolf, T.; Kant, Ch.; Mayr, F.; Loidl, A.

doi:10.1103/physrevb.77.024421

Cited by 38 publications

(48 citation statements)

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“…1(b)]. The pure lattice contributions due to deviations from the cubic symmetry in the magnetically ordered state were estimated in the case of MnO and NiO to be less than 1% of the phonon eigenfrequencies [6,27], while the exchange-driven and experimentally observed splittings are one order of magnitude larger [28][29][30].In the case of the spinel systems ACr 2 O 4 with nonmagnetic ions A = Zn, Mg, Cd, the magnetic properties are determined by Cr 3+ ions with spin S = 3/2 in octahedral environment. The Cr sites form a pyrochlore lattice which can be regarded as a network of cornersharing tetrahedra [see Fig.…”

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Universal Exchange-Driven Phonon Splitting in Antiferromagnets

et al. 2012

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We report a linear dependence of the phonon splitting ∆ω on the non-dominant exchange coupling constant J nd in the antiferromagnetic transition-metal monoxides MnO, FeO, CoO, NiO, and in the frustrated antiferromagnetic oxide spinels CdCr2O4, MgCr2O4, and ZnCr2O4. It directly confirms the theoretical prediction of an exchange induced splitting of the zone-centre optical phonon for the monoxides and explains the magnitude and the change of sign of the phonon splitting on changing the sign of the non-dominant exchange also in the frustrated oxide spinels. The experimentally found linear relationh∆ω = βJ nd S 2 with slope β = 3.7 describes the splitting for both systems and agrees with the observations in the antiferromagnets KCoF3 and KNiF3 with perovskite structure and negligible next-nearest neighbour coupling. The common behavior found for very different classes of cubic antiferromagnets suggests a universal dependence of the exchange-induced phonon splitting at the antiferromagnetic transition on the non-dominant exchange coupling.The interplay of magnetism and the underlying crystal lattice is a topical issue of condensed-matter physics. This spin-phonon coupling can relieve frustration via a spin-driven Jahn-Teller effect in frustrated magnets [1,2], lead to novel excitations such as electromagnons in multiferroics [3,4], and can even bear the potential for future applications via magneto-dielectric effects [5]. For transition-metal monoxides (TMMOs) a magnetisminduced anisotropy in the lattice response was predicted theoretically [6]. This approach has been extended to other material classes such as Cr based spinels, which are hallmark systems for highly frustrated magnets [7][8][9][10], where spin-phonon coupling leads to a splitting of characteristic phonon modes [11][12][13][14][15].TMMOs are both textbook examples for antiferromagnets governed by superexchange in a cubic rock-salt lattice and benchmark materials for the understanding of strongly correlated electronic systems [16,17]. The magnetic structure of the TMMOs consists of ferromagnetic planes coupled antiferromagnetically, e.g., along [1 1 1] as depicted in Fig. 1(a). The antiferromagnetic 180• nextnearest neighbor (nnn) exchange J 2 is supposed to be the driving force of the magnetic ordering [18,19], leaving the nearest-neighbor (nn) exchange J 1 frustrated, since it cannot satisfy all its pairwise interactions [see Fig. 1(c)]. In Fig.1(d) , and find a linear slope of k B T N /J 2 S(S + 1) ∼ 3 (solid line) close to the expected relation in mean-field approximation (dashed line). In a pioneering paper Massidda et al. [6] showed that even for purely cubic TMMOs the antiferromagnetic order is accompanied by a Borneffective-charge redistribution from spherical to cylindrical with the antiferromagnetic axis being the symmetry axis, e.g. [1 1 1]. Consequently, the cubic zone-centre optical phonon is predicted to split into two phonon modes with eigenfrequencies ω and ω ⊥ for light polarized parallel and perpendicular to the cylindrical axis, resp...

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Universal Exchange-Driven Phonon Splitting in Antiferromagnets

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“…6,7,8,9,10 The microscopic nature of the magnetoelectric effects can be better understood through the studies of the optical excitations such as IR active electromagnons and lattice vibrations that are modified by the spin-lattice interaction. 11,12,13,14,15,16,17,18,19 Due to the coincidence of the temperatures for the FM ordering of Dy spins and the AFE lattice ordering in Dy-IG, we expected an interesting behavior for the low-frequency optical phonons, which are related to the displacements of the heaviest ions (Dy) and spin-related ligand field (LF) transitions and Kaplan-Kittel (KK) 20 magnetic exchange resonance modes in Dy-IG. The main results of this paper are (i) the observed correlation between the magnetic field-induced changes of magnetic susceptibility in Dy-IG is followed by the discussion of the experimental data.…”

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Far-infrared spectra of the magnetic exchange resonances and optical phonons and their connection to magnetic and dielectric properties of Dy3Fe5O
Kang
¹
,
Standard
²
,
Rogers
³

et al. 2012
Phys. Rev. B
17
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Far-infrared spectra of ferrimagnetic Dy 3 Fe 5 O 12 single crystals have been studied in the spectral range between 12 and 700 cm -1 and in a wide temperature range between 5 K and 300 K using transmission spectroscopy and rotating analyzer ellipsometry. In the temperature range below T C =16 K for the magnetic ordering of Dy 3+ spins, a number of ligand field (LF) and Kaplan-Kittel (KK) exchange resonance modes have been found. Temperature dependences of their frequencies allowed us to estimate the ratio between the Fe−Dy and Dy−Dy exchange constants.We found that variation of the oscillator strength of the KK modes correlates with the magnetic field induced changes of magnetic permeability. The low temperature peak in the static value of the dielectric function at T C =16 K may be related to the observed temperature-induced variation of the oscillator strength of the optical phonons.

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“…In the last decades the lattice vibrations of TM monoxides have been investigated quite intensively with experimental techniques [12][13][14][15][16] . Calculations, however, have been more sparse [17][18][19][20][21][22] and, with the exception of Ref.…”

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Vibrational properties of MnO and NiO from DFT+U-based density functional perturbation theory

et al. 2011

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We introduce an extension of the density functional perturbation theory (DFPT) that allows self-consistent linear-response calculations from a DFT + U ground state. Using this scheme, the full phonon dispersion of strongly correlated materials, whose ground state can be captured with Hubbard-corrected functionals, can be accessed with unprecedented accuracy and numerical efficiency. The tool is applied to the study of MnO and NiO in their antiferromagnetic (AFII) ground state. Our results confirm the highly noncubic behavior of these systems and show a strong interplay between features of the phonon spectrum and the occupation of specific d states, suggesting the possibility to investigate the electronic structure of these materials through the analysis of their phonon spectrum

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Magnetic-order induced phonon splitting in MnO from far-infrared spectroscopy

Cited by 38 publications

References 37 publications

Universal Exchange-Driven Phonon Splitting in Antiferromagnets

Universal Exchange-Driven Phonon Splitting in Antiferromagnets

Far-infrared spectra of the magnetic exchange resonances and optical phonons and their connection to magnetic and dielectric properties of Dy3Fe5O
Kang
¹
,
Standard
²
,
Rogers
³

et al. 2012
Phys. Rev. B
17
1
5
0
View full text Add to dashboard Cite

Vibrational properties of MnO and NiO from DFT+U-based density functional perturbation theory

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Magnetic-order induced phonon splitting in MnO from far-infrared spectroscopy

Cited by 38 publications

References 37 publications

Universal Exchange-Driven Phonon Splitting in Antiferromagnets

Universal Exchange-Driven Phonon Splitting in Antiferromagnets

Far-infrared spectra of the magnetic exchange resonances and optical phonons and their connection to magnetic and dielectric properties of Dy3Fe5OKang1, Standard2, Rogers3 et al. 2012Phys. Rev. B17150View full textAdd to dashboardCite

Vibrational properties of MnO and NiO from DFT+U-based density functional perturbation theory

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Far-infrared spectra of the magnetic exchange resonances and optical phonons and their connection to magnetic and dielectric properties of Dy3Fe5O
Kang
¹
,
Standard
²
,
Rogers
³

et al. 2012
Phys. Rev. B
17
1
5
0
View full text Add to dashboard Cite