Theory of High-Temperature Multiferroicity in Cupric Oxide

Tolédano, Pierre; Leo, Naëmi; Khalyavin, D. D.; Chapon, L. C.; Hoffmann, Tim; Meier, Dennis; Fiebig, Manfred

doi:10.1103/physrevlett.106.257601

Cited by 50 publications

(67 citation statements)

References 16 publications

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“…In contrast with the conclusions of Refs. [8][9][10], our analysis based on rigorous symmetry arguments indicates that there must be a collinear intermediate phase (AF3) between the paramagnetic and spiral AF2 states. Such a phase has been shown, both theoretically and experimentally, to occur in other geometrically frustrated antiferromagnets where symmetry allows for uniaxial anisotropy at second order [14,15] For the purpose of this study, a CuO sample was grown using a floating zone technique as described in Ref.…”

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confidence: 89%

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Magnetic Phase Diagram of CuO via High-Resolution Ultrasonic Velocity Measurements

et al. 2012

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High resolution ultrasonic velocity measurements have been used to determine the temperaturemagnetic-field phase diagram of the monoclinic multiferroic CuO. A new transition at TN3 = 230 K, corresponding to an intermediate state between the antiferromagnetic non-collinear spiral phase observed below TN2 = 229.3 K and the paramagnetic phase, is revealed. Anomalies associated with a first order transition to the commensurate collinear phase are also observed at TN1 = 213 K. For fields with B b, a spin-flop transition is detected between 11 T -13 T at lower temperatures. Moreover, our analysis using a Landau-type free energy clearly reveals the necessity for an incommensurate collinear phase between the spiral and the paramagnetic phase. This model is also relevant to the phase diagrams of other monoclinic multiferroic systems.PACS numbers: 75.30.Kz, 75.85.+t, 75.30.Gw Multiferroic phenomena have been a subject of intense interest in recent decades arising from opportunities to explore new fundamental physics as well as possible technological applications [1][2][3]. Coupling between different ferroic orders has been proven to be driven by several different types of mechanisms. In particular, multiferroics with a spiral spin-order-induced ferroelectricity have revealed high spontaneous polarization and strong magnetoelectric coupling [4,5]. Cupric oxide (CuO), the subject of this letter, was characterized as a magnetoelectric multiferroic four years ago when it was shown that its ferroelectric order is induced by the onset of a spiral antiferromagnetic (AFM) order at an unusually high temperature of 230 K [3]. Thus far, two AFM states have been reported, a low temperature (T N 1 ∼ 213 K) AF1 commensurate collinear state with the magnetic moments along the monoclinic b axis and an AF2 incommensurate spiral state with half of the magnetic moments in the ac plane (T N 2 ∼ 230 K) [3,6,7]. However, the authors of the neutron diffraction measurements [6] Encouraged by recent experiments on other multiferroic systems using ultrasonic measurements [11], we measured the temperature and field dependence of the velocity of transverse modes in order to determine the magnetic phase diagram of CuO. A new transition is detected at T N 3 = 230 K just above the AF2 spiral phase observed at T N 2 = 229.3 K, while the first order transition is observed at T N 1 = 213 K. Furthermore, dielectric constant measurements confirm that only the spiral phase (between T N 1 and T N 2 ) supports a spontaneous electric polarization. In addition, we report on a spin-flop transition in the low temperature AF1 collinear phase when B b. Thus, based on these findings, a new magneticfield vs temperature phase diagram is proposed for CuO. In order to elucidate the possible nature of the AFM states observed in CuO, a non-local Landau-type free energy is also developed for CuO and similar monoclinic multiferroics. This approach has been very successful in explaining the magnetic phase diagrams of other multiferroic systems [12][13][14]. In contrast w...

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confidence: 89%

“…However, the authors of the neutron diffraction measurements [6] questioned the possibility of having a direct condensation from a paramagnetic (PM) phase to a spiral magnetic phase. Despite this remark, a recent Landau theory [8], as well as several Monte-Carlo simulations [9,10], appear to support this sequence of magnetic orderings.…”

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confidence: 92%

Magnetic Phase Diagram of CuO via High-Resolution Ultrasonic Velocity Measurements

et al. 2012

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“…A phenomenological theory of phase transitions in CuO was suggested in [26], in which the phase transition PM-AF2 was described using the triggering mechanism. This implies the first order character of the PM-AF2 transition.…”

Section: Cuomentioning

confidence: 99%

“…Therefore, one can describe the phase transitions in CuO using the commensurate wave vector k c and account for longwavelength modulation by Lifshitz invariants allowed by the symmetry [20]. Using the monoclinic structure as reference it was shown that the magnetic structure of the phase AF2 is described by two IR's B 1 and B 2 , whereas the phase AF1 by B 2 [20,21,26].…”

Section: Cuomentioning

confidence: 99%

Interpretation of magnetoelectric phase states using the praphase concept and exchange symmetry

Ter-Oganessian¹,

Sakhnenko²

2013

J. Phys.: Condens. Matter

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Abstract. The majority of magnetoelectric crystals show complex temperaturemagnetic field or temperature-pressure phase diagrams with alternating antiferromagnetic incommensurate, magnetoelectric, and commensurate phases. Such phase diagrams occur as a result of successive magnetic instabilities with respect to different order parameters, which usually transform according to different irreducible representations (IR) of the space group of the crystal. Therefore, in order to build a phenomenological theory of phase transitions in such magnetoelectrics one has to employ several order parameters and assume the proximity of various instabilities on the thermodynamic path. In this work we analyze the magnetoelectrics MnWO 4 , CuO, NaFeSi 2 O 6 , NaFeGe 2 O 6 , Cu 3 Nb 2 O 8 , α-CaCr 2 O 4 , and FeTe 2 O 5 Br using the praphase concept and the symmetry of the exchange Hamiltonian. We find that in all the considered cases the appearing magnetic structures are described by IR's entering into a single exchange multiplet, whereas in the cases of MnWO 4 and CuO by a single IR of the space group of the praphase structure. Therefore, one can interpret the complex phase diagrams of magnetoelectrics as induced by a single IR either of the praphase or of the symmetry group of the exchange Hamiltonian. Detailed temperature-magnetic field phase diagrams of MnWO 4 and CuO for certain field directions are obtained and the magnetic structures of the field-induced phases are determined.

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“…1c. This phase exhibits a static electric polarization P b B100 mC m À 2 along b 20,26,27 , the origin of which has been discussed in the context of weakly frustrated intersublattice spin interactions 23 , magnetic degeneracy and the spin-orbit interaction 28 and cross-coupled AFM order parameters 29 . While CuO exhibits ferroelectric hysteresis loops 20 and chiral magnetic domains that can be switched electrically 27 , no substantial uniform static magnetoelectric coupling has been found in polycrystalline CuO up to 7 T 26 , and the AF2 phase appears to be stable to at least 16 T 30 .…”

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confidence: 99%

High-temperature electromagnons in the magnetically induced multiferroic cupric oxide driven by intersublattice exchange

et al. 2014

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Magnetically induced ferroelectric multiferroics present an exciting new paradigm in the design of multifunctional materials, by intimately coupling magnetic and polar order. Magnetoelectricity creates a novel quasiparticle excitation-the electromagnon-at terahertz frequencies, with spectral signatures that unveil important spin interactions. To date, electromagnons have been discovered at low temperature (o70 K) and predominantly in rare-earth compounds such as RMnO 3 . Here we demonstrate using terahertz time-domain spectroscopy that intersublattice exchange in the improper multiferroic cupric oxide (CuO) creates electromagnons at substantially elevated temperatures (213-230 K). Dynamic magnetoelectric coupling can therefore be achieved in materials, such as CuO, that exhibit minimal static cross-coupling. The electromagnon strength and energy track the static polarization, highlighting the importance of the underlying cycloidal spin structure. Polarized neutron scattering and terahertz spectroscopy identify a magnon in the antiferromagnetic ground state, with a temperature dependence that suggests a significant role for biquadratic exchange.

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Theory of High-Temperature Multiferroicity in Cupric Oxide

Cited by 50 publications

References 16 publications

Magnetic Phase Diagram of CuO via High-Resolution Ultrasonic Velocity Measurements

Magnetic Phase Diagram of CuO via High-Resolution Ultrasonic Velocity Measurements

Interpretation of magnetoelectric phase states using the praphase concept and exchange symmetry

High-temperature electromagnons in the magnetically induced multiferroic cupric oxide driven by intersublattice exchange

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