Evolution of the Magnetic Structure of Hexagonal HoMnO<sub>3</sub> from Neutron Powder Diffraction Data

Muñoz, Amalia; Alonso, J. A.; Martı́nez-Lope, M. J.; Casáis, M. T.; Martínez, José Luis; Fernandez-Diaz, M. T.

doi:10.1021/cm0012264

Cited by 156 publications

(153 citation statements)

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“…Dielectric anomalies at the magnetic transitions in REMnO 3 have first been observed in Y MnO 3 at the Néel temperature 1 and were later found at T N in other hexagonal RE-MnO 3 compounds, [7][8][9] suggesting the coupling between the magnetic and ferroelectric orders. They are of particular physical interest because, by symmetry arguments, a direct coupling between the in-plane staggered magnetization and the c-axis polarization in the P6 3 cm structure is not allowed.…”

Section: Introductionmentioning

confidence: 88%

“…The rare-earth moment can interact with the Mn 3+ spins and the dielectric polarization and thus increase the complexity of the phase diagram and the physical phenomena that can be observed. For example, the magnetic phase diagram of HoMnO 3 studied by neutron scattering 3,4 and second harmonic generation optical experiments 5,6 shows two additional phase transitions below T N indicating subtle changes in the magnetic order of the Mn 3+ and Ho 3+ ions at zero external magnetic field. At T SR Ϸ 33 K a sharp Mn-spin reorientation transition takes place at which all Mn-moments rotate in-plane by an angle of 90°c hanging the magnetic symmetry from P6 គ 3 c គm ͑T Ͼ T SR ͒ to P6 គ 3 cm គ ͑T Ͻ T SR ͒.…”

Section: Introductionmentioning

confidence: 99%

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Field-induced phases inHoMnO3at low temperatures

et al. 2005

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The field-induced re-entrant phase in multiferroic hexagonal HoMnO 3 is investigated to lower temperatures by dc magnetization, ac susceptibility, and specific heat measurements at various magnetic fields. Two new phases have been unambiguously identified below the Néel transition temperature, T N = 76 K, for magnetic fields up to 50 kOe. The existence of an intermediate phase between the P6 គ 3 c គm and P6 គ 3 cm គ magnetic structures ͑previously predicted from dielectric measurements͒ was confirmed and the magnetic properties of this phase have been investigated. At low temperatures ͑T Ͻ 5 K͒ a dome shaped phase boundary characterized by a magnetization jump and a narrow heat capacity peak was detected between the magnetic fields of 5 kOe and 18 kOe. The transition across this phase boundary is of first order and the magnetization and entropy jumps obey the magnetic analogue of the Clausius-Clapeyron relation. Four of the five low-temperature phases coexist at a tetracritical point at 2 K and 18 kOe. The complex magnetic phase diagram so derived provides an informative basis for unraveling the underlying driving forces for the occurrence of the various phases and the coupling between the different orders.

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Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Field-induced phases inHoMnO3at low temperatures

et al. 2005

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“…5,10,12,14,16 The lowtemperature anomaly of ͑T͒ at T 2 = 5.2 K and its magnetic field dependence is shown in Fig. 1.…”

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confidence: 99%

“…2 are not completely resolved. Neutron scattering 12,16 and optical investigations 10 have assigned the P6 គ 3 c គm, P6 គ 3 cm គ , and P6 3 cm magnetic symmetries to HT1, HT2, and the phase below 5 K ͑enclosed by T 2 , T 5 , and T 3 in Fig. 2͒, respectively.…”

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confidence: 99%

Low-temperature dielectric anomalies inHoMnO3: The complex phase diagram

Yen

Cruz²,

Lorenz³

et al. 2005

Phys. Rev. B

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The dielectric constant of multiferroic hexagonal HoMnO 3 exhibits an unprecedented diversity of anomalies at low temperatures ͑1.8 K Ͻ T Ͻ 10 K͒ and under external magnetic fields related to magnetic phase transitions in the coupled system of Ho moments, Mn spins, and ferroelectric polarization. The derived phase diagram is far more complex than previously assumed including reentrant phases, phase transitions with distinct thermal and field hysteresis, as well as several multicritical points. Magnetoelastic interactions introduce lattice anomalies at the magnetic phase transitions. Among the multiferroic compounds hexagonal rare-earth manganites, RMnO 3 ͑R = Sc, Y, Ho to Lu͒, have attracted recent attention because of the coexistence of antiferromagnetic ͑AFM͒ and ferroelectric ͑FE͒ orders below their Néel temperatures, T N Ͻ 100 K. The mutual interference and the possible correlation of magnetic and ferroelectric orders are of fundamental interest and of significance for prospective applications. Since the report 1 of a dielectric anomaly at T N of YMnO 3 and later observations of similar effects in other hexagonal RMnO 3 the origin of the magnetodielectric coupling in these compounds has been a matter of discussion. 2-5In the magnetic symmetries realized just below T N the direct coupling between the in-plane staggered AFM magnetization and the c-axis FE polarization is not allowed. 6 The indirect coupling via lattice strain or other secondary effects has therefore been proposed. 5 In fact, the existence of strong spin-phonon interactions was concluded from the anomalous temperature dependence of the thermal conductivity 7 and the thermal expansion anomalies observed at T N of HoMnO 3 . 8 The magnetic order below 100 K is very complex for some RMnO 3 and it is determined by the strong in-plane AFM superexchange interaction of the Mn 3+ spins and their geometric frustration in the P6 3 cm hexagonal structure. While strong in-plane magnetic correlations exist well above the Néel temperature 8,9 the long-range AFM order of the Mn 3+ sets in only below 100 K with a frustrated, noncollinear spin arrangement ͑neighboring moments form an angle of 120°͒. The different spin arrangements and magnetic symmetries compatible with the P6 3 cm crystalline structure have been discussed in detail by Fiebig et al. 10 The direct magnetic exchange of the R 3+ ions, essential at low temperatures, and the coupling of the rare-earth moments with the Mn spins as well as the FE polarization gives rise to a wealth of interesting physical phenomena and a complex magnetic phase diagram. Several subsequent magnetic phase changes have been observed in HoMnO 3 below T N = 76 K, including a sharp Mn spin-rotation transition at T SR = 33 K with the onset of AFM Ho-moment order and another transition at about 5 K involving a major increase of the Ho 3+

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“…To demonstrate the structure-resolving power of the spherical harmonic analysis method on XFH data, we applied it to a hexagonal HoMnO 3 structure (space group P63cm, a = 6.1413 Å, c = 11.4122Å ) [20]. HoMnO3 is an important multiferroic structure [21].…”

Section: The Integral Function In (11)mentioning

confidence: 99%

Direct extraction of quantitative structural information from x-ray fluorescence holograms using spherical-harmonic analysis

2012

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Evolution of the Magnetic Structure of Hexagonal HoMnO₃ from Neutron Powder Diffraction Data

Cited by 156 publications

References 33 publications

Field-induced phases inHoMnO3at low temperatures

Field-induced phases inHoMnO3at low temperatures

Low-temperature dielectric anomalies inHoMnO3: The complex phase diagram

Direct extraction of quantitative structural information from x-ray fluorescence holograms using spherical-harmonic analysis

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Evolution of the Magnetic Structure of Hexagonal HoMnO3 from Neutron Powder Diffraction Data

Cited by 156 publications

References 33 publications

Field-induced phases inHoMnO3at low temperatures

Field-induced phases inHoMnO3at low temperatures

Low-temperature dielectric anomalies inHoMnO3: The complex phase diagram

Direct extraction of quantitative structural information from x-ray fluorescence holograms using spherical-harmonic analysis

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Evolution of the Magnetic Structure of Hexagonal HoMnO₃ from Neutron Powder Diffraction Data