Spiral Spin Structure in the Commensurate Magnetic Phase of Multiferroic RMn2O5

Kimura, Hiroyuki; Kobayashi, Satoru; Fukuda, Yoshikazu; Osawa, Toshihiro; Kamada, Youichi; Noda, Yukio; Kagomiya, Isao; Kohn, Kay

doi:10.1143/jpsj.76.074706

Cited by 64 publications

(105 citation statements)

References 24 publications

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“…The latter has two main origins; (i) changes of the angle between atoms in the superexchange bridge that affects the strength of the corresponding interactions, 6 and (ii) changes of the local structure in the vicinity of the magnetic ion, determining its local crystal-field anisotropy. [7][8][9] As a result, significantly different magnetic states can be realized, from which only a few may be multiferroic. The prominent examples of such experimental approach are studies of RMnO 3 , where the radius of the rare-earth ion R influences the Mn-O-Mn angle and thus selects between non-ferroelectric collinear and multiferroic spiral magnetic ground states.…”

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confidence: 99%

Multiferroicity in the geometrically frustrated FeTe2O5Cl

Pregelj

Zorko

Zaharko³

et al. 2013

Phys. Rev. B

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The layered FeTe2O5Cl compound was studied by specific-heat, muon spin relaxation, nuclear magnetic resonance, dielectric, as well as neutron and synchrotron x-ray diffraction measurements, and the results were compared to isostructural FeTe2O5Br. We find that the low-temperature ordered state, similarly as in FeTe2O5Br, is multiferroic -the elliptical amplitude-modulated magnetic cycloid and the electric polarization simultaneously develop below 11 K. However, compared to FeTe2O5Br, the magnetic elliptical envelop rotates by 75(4)• and the orientation of the electric polarization is much more sensitive to the applied electric field. We propose that the observed differences between the two isostructural compounds arise from geometric frustration, which enhances the effects of otherwise subtle Fe 3+ (S = 5/2) magnetic anisotropies. Finally, x-ray diffraction results imply that, on the microscopic scale, the magnetoelectric coupling is driven by shifts of the O1 atoms, as a response to the polarization of the Te 4+ lone-pair electrons involved in the Fe-O-Te-O-Fe exchange bridges.

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Section: Introductionmentioning

confidence: 99%

Multiferroicity in the geometrically frustrated FeTe2O5Cl

Pregelj

Zorko

Zaharko³

et al. 2013

Phys. Rev. B

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“…The magnetic phase diagram can be separated into three or four regions depending on the rare-earth. 10,11 Below T N , the system first enters a 2D incommensurate (HT-ICM) phase, which is characterized by a wave vector q = (q x 0 q z ). On further cooling the magnetic structure will lock in either a 1D incommensurate phase (1D-ICM) with q = (q x 0 1 4 ), depending on the rare-earth, or directly transform to the commensurate state (CM), where q = ( 10 The 1D-ICM exists only in a small range of approximately 1 K around T C1 .…”

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Magnetic structure and electric field effects in multiferroic YMn2O5

et al. 2011

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The magnetic structure of multiferroic RMn2O5 (R=Y,Er) has been investigated by means of resonant soft x-ray diffraction. Energy, temperature and azimuthal angle scans were performed in addition to reciprocal space maps on the magnetic reflection in the different magnetic phases of YMn2O5. We also investigated the orbital magnetic moment at the oxygen K-edge for RMn2O5 with both, R= Y and Er compositions. These moments reflect the strong hybridization between Mn 3d and oxygen 2p states. Experiments with applied electric fields are additionally presented, showing that the helical component of the magnetic structure in the CM phase of YMn2O5 can be reversed by the application of an electric field. However, the incommensurate magnetic reflection in the high temperature phase is unaffected. Interestingly, this is observed only in the presence of a small electrical current, indicative of a current induced/enhanced switching of magnetic domains.

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“…5,10 [16][17][18][19] This spiral-spin order also breaks the inversion symmetry 3,20 and it was considered as an alternative mechanism for ferroelectricity in these compounds. [16][17][18]21 The essential difference between the two proposed mechanisms is the microscopic nature of the exchange coupling that has to be involved. In the spin current ͑spiral͒ model, 22,23 the weak antisymmetric DzyaloshinskiiMoriya interaction ͑ϳS ជ i ϫ S ជ j ͒ creates the magnetoelectric coupling, whereas in the exchange striction model, the FE polarization has its origin in the ionic displacements lifting the frustration of spins interacting via the symmetric exchange ͑or superexchange͒ interactions ͑ϳS ជ i · S ជ j ͒.…”

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Pressure-induced polarization reversal in multiferroicYMn2O5

et al. 2008

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The low-temperature ferroelectric polarization of multiferroic YMn 2 O 5 is completely reversed at a critical pressure of 10 kbar and the phase transition from the incommensurate to the commensurate magnetic phase is induced by pressures above 14 kbar. The high-pressure data correlate with thermal-expansion measurements, indicating a significant lattice strain at the low-temperature transition into the incommensurate phase. The results support the exchange striction model for the ferroelectricity in multiferroic RMn 2 O 5 compounds and they show the importance of magnetic frustration as well as the spin-lattice coupling. DOI: 10.1103/PhysRevB.77.220104 PACS number͑s͒: 77.80.Ϫe, 75.30.Ϫm, 75.50.Ee, 77.84.Bw Multiferroic magnetoelectric compounds in which ferroelectricity and magnetic order coexist and mutually interact have been in the focus of attention very recently because of a wealth of novel physical phenomena observed in these complex materials.1-4 Among the family of multiferroics, the RMn 2 O 5 ͑R ϭ rare earth, Y, Bi͒ manganites are of significant interest because of their extreme complexity with transitions between different commensurate magnetic structures ͑CM͒ and incommensurate ͑IC͒ magnetic structures ͑ICM͒, some of which exhibit ferroelectricity induced by frustrated magnetic orders.5-10 Their common phase sequence upon decreasing temperature T includes transitions from the high-T paramagnetic and paraelectric ͑PE͒ to an antiferromagnetic ͑AFM͒ but still PE phase at T N1 Ӎ 44 K, with an IC magnetic modulation along the orthorhombic a and c axes. At T C1 Ӎ 39 K, a lock-in transition takes place into a CM magnetic phase ͓q ជ = ͑0.5, 0 , 0.25͔͒, which is ferroelectric ͑FE͒. At lower temperature T C2 , all RMn 2 O 5 compounds experience another transition where q ជ unlocks again into different IC values and the FE polarization shows a sharp drop ͑but not necessarily to zero͒. Additional changes of the magnetic order that are identified as spin reorientations in the CM phase have been reported for some RMn 2 O 5 , for example DyMn 2 O 5 ͑Ref. 9͒ and HoMn 2 O 5 .11 It is remarkable that all magnetic ͑and FE͒ phase transitions are clearly resolved in anomalies of the dielectric constant, the FE polarization, and the thermal expansivities, which proves the prominent role of the spin-lattice coupling in the multiferroic properties of these compounds.11,12 The origin of the phase complexity of RMn 2 O 5 lies in the peculiarities of the lattice structure with different magnetic ions ͑Mn 4+ ,Mn 3+ , rare earth͒ and a multitude of partially competing superexchange interactions, leading to a high degree of frustration in the magnetic system. 7 In particular, the smallest loop of nearest-neighbor Mn ions with AFM exchange interactions in the a-b plane has five members, which naturally leads to geometric frustration of the Mn spins.11 Frustrated systems are susceptible to small perturbations such as magnetic fields or pressure, since many different magnetic structures are close in energy and compete for the gro...

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Spiral Spin Structure in the Commensurate Magnetic Phase of Multiferroic RMn₂O₅

Cited by 64 publications

References 24 publications

Multiferroicity in the geometrically frustrated FeTe2O5Cl

Multiferroicity in the geometrically frustrated FeTe2O5Cl

Magnetic structure and electric field effects in multiferroic YMn2O5

Pressure-induced polarization reversal in multiferroicYMn2O5

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