Structural and magnetic studies of mechanically activated ErMnO3

Федорова, О. М.; Кожина, Г. А.; Упоров, С. А.

doi:10.1016/j.jallcom.2017.12.372

Cited by 5 publications

(3 citation statements)

References 26 publications

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“…73 A most distinctive temperature dependent phonon profile is found associated with a torsional mode involving oxygen displacements dynamically correlated to the negative thermal expansion along the c axis. 50, 60 It has a nearly fully screened macroscopic field in the intermediate phase where it is also found mediating in bipolaron conception. Below the lock-in ferroelectric transition at ~830 K it turns into a well-defined asymmetric band, at 288 cm -1 -329 cm -1 (300 K), that having one remaining component partially screened further splits as spin-phonon interactions become significant and the unit cell tripling takes place.…”

Section: Discussionmentioning

confidence: 99%

h−ErMnO3 absorbance, reflectivity, and emissivity in the terahertz to mid-infrared from 2 to 1700 K: Carrier screening, Fröhlich resonance, small polarons, and bipolarons

et al. 2020

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We report the temperature dependent THz to mid-infrared response of hexagonal-ErMnO3 using absorption, reflectivity, and emissivity techniques from 2 K to 1700 K. At low temperatures, lowest frequency vibrational modes which extend up the lock-in ferroelectric temperature, coexist with paramagnon excitations and are associated with well-defined crystal field Rare Earth pure magnetic replicas in an intriguing phonon-magnetic convergence enhancing the multiferroic character of h-ErMnO3. Increasing the temperature, a number of vibrational bands close to the space group predicted undergo profile broadening and softening. In particular, a distinctive set of bands in the 288-329 cm -1 (300 K) range has a component whose profile is carrier screened becoming nearly fully blurred in the intermediate phase between ~830 K and ~1500 K. Below TC ~830 K this asymmetric band, having one component still partially screened, further splits as spin phonon interaction and the tripling of the unit cell takes place revealing at TN ~79 K a delicate balance of long-and short-range interactions. Ambient Raman scattering brings up evidence of a Fröhlich resonance due to Coulomb interactions between carriers and the macroscopic field linked to the corresponding longitudinal optical phonon mode. We found it is dynamically correlated to the hexagonal c-axis negative thermal expansion. Quantitative analyses of the mid-infrared (MIR) optical conductivity show that also plays a role in small polarons and mediates in high temperature bipolarones.Bipolaron profiles at high temperatures change as the sample opacity increases when at ~900 K straight stripes turn curly toward complex vortex-antivortex domain patterns in the paraelectric phase. At still higher temperatures a low frequency Drude contribution is triggered by electron hopping signaling an insulator-metal phase transition at ~1600 K while the MIR response suggests coexistence between single small polarons and bipolarons. On closing, we draw a parallel with improper ferroelectrics sustaining a lattice incommensurate intermediate phase and unit cell tripling. We argue that in the h-RMnO3 (R=Rare Earth, Y) family of compounds the intermediate phase be considered incommensurate with onset at TINC ~1500 K and ferroelectric lock-in at TC ~830 K delimiting this regime in h-ErMnO3.

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Section: Discussionmentioning

confidence: 99%

h−ErMnO3 absorbance, reflectivity, and emissivity in the terahertz to mid-infrared from 2 to 1700 K: Carrier screening, Fröhlich resonance, small polarons, and bipolarons

et al. 2020

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“…Members of the family of multiferroic hexagonal manganites, RMnO3 (R = Sc, Y, In, Dy-Lu), are ferroelectric due to a structural phase transition within the interval ~1000-1500 K [1][2][3][4][5] and antiferromagnetic due to a magnetic ordering transition within the interval ~60-130 K [6][7][8][9][10]. Their structures at high temperatures and at room temperature are in space groups P63/mmc and P63cm, respectively [3,5,[10][11][12][13]. The structural transition P63/mmc → P63cm includes a geometrical tilt that displaces charged atoms in the structure, resulting in spontaneous polarization oriented along the crystallographic caxis and making it improper ferroelectric [5,12,14,15].…”

Section: Introductionmentioning

confidence: 99%

Magnetoelastic properties of multiferroic hexagonal ErMnO3

Fernández-Posada

Haines

Evans

et al. 2022

Journal of Magnetism and Magnetic Materials

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“…In h-ErMnO3, the competition between different magnetic exchange interactions involving the Mn and Er sublattices gives rise to the appearance of several magnetic phase transitions over a temperature range going from 1000 K down to the liquid helium temperature [41][42][43][44][45][46][47][48][49][50]. Therefore, a paraelectric to ferroelectric transition is observed at about 833 K, while the Mn magnetic moments order antiferromagnetically close to 80 K. The Er magnetic moments usually undergo ordering transitions below 10 K. It is worth noting that the Mn magnetic moments are strongly frustrated in the-ab plane within a triangular structure, making marginal their contribution to the total magnetization even under intense magnetic fields [41][42][43][44][45][46][47][48][49][50]. For this purpose, our present study of the magnetocaloric properties of h-ErMnO3 single crystals is motivated mainly by the large anisotropy expected in the temperature range around 10 K, where the ordering state of Er magnetic moments can be easily manipulated under relatively low driving magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

Unusual rotating magnetocaloric effect in the hexagonal ErMnO3 single crystal

et al. 2018

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It is known that orthorhombic RMnO3 multiferroics (R = magnetic rare earth) with low symmetry exhibit a large rotating magnetocaloric effect because of their strong magnetocrystalline anisotropy. In this paper, we demonstrate that the hexagonal ErMnO3 single crystals also unveils a giant rotating magnetocaloric effect that can be obtained by spinning them in constant magnetic fields around their a or b axes. When the ErMnO3 crystal is rotated with the magnetic field initially parallel to the c-axis, the resulting entropy change reaches maximum values of 7, 17 and 20 J/kg K under a constant magnetic field of 2, 5 and 7 T, respectively. These values are comparable or even larger than those shown by some of the best orthorhombic phases. More interestingly, the generated anisotropic thermal effect is about three times larger than that exhibited by the hexagonal HoMnO3 single crystal.The enhancement of the rotating magnetocaloric effect in the hexagonal ErMnO3 compound arises from the unique features of Er 3+ magnetic sublattice. In fact, the Er 3+ magnetic moments located at 2a sites experience a first-order metamagnetic transition close to 3 K along the c-axis resulting in a peaked magnetocaloric effect over a narrower temperature range. In contrast, the "paramagnetic" behaviour of Er 3+ magnetic moments within the ab-plane, produces a larger magnetocaloric effect over a wider temperature range. Therefore, the magnetocaloric effect anisotropy is maximized between the c and the ab-directions, leading to a giant rotating magnetocaloric effect. *Mohamed.balli@usherbrooke.ca I. IntroductionBased on the well-known magnetocaloric effect (MCE), magnetic cooling is a trending technology that continues to attract a worldwide interest due to its potential high thermodynamic efficiency as well as its ecofriendly character [1][2][3][4][5][6][7][8]. The implementation of this emergent technology in our daily life would enable to fully suppress the harmful synthetic refrigerants such as fluorinated fluids, usually present in standard refrigerators and air-conditioners [1][2][3][4][5][6][7][8], thus allowing to meet the requirements of several treaties that were universally adopted by the international community aiming to reduce the utilization of CFCs, HCFCs and HFCs gases and, green house gases (GHG) emissions [1]. However, the search for advanced magnetocaloric materials with outstanding thermal, chemical and mechanical properties is necessary for the transfer of magnetic refrigeration technology towards the market place. In this context, a large MCE has been pointed out in a wide variety of magnetocaloric materials including both intermetallics and oxides [1-8]. Some of them such as LaFe13-xSix compounds, Fe2P-type materials and ABO3-based oxides have been successfully tested in room-temperature devices unveiling the bright future of magnetic refrigeration [1]. On the other hand, magnetic materials with excellent caloric effects at the temperature range below 30 K are of great importance in several low-temperature applications...

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Structural and magnetic studies of mechanically activated ErMnO3

Cited by 5 publications

References 26 publications

h−ErMnO3 absorbance, reflectivity, and emissivity in the terahertz to mid-infrared from 2 to 1700 K: Carrier screening, Fröhlich resonance, small polarons, and bipolarons

h−ErMnO3 absorbance, reflectivity, and emissivity in the terahertz to mid-infrared from 2 to 1700 K: Carrier screening, Fröhlich resonance, small polarons, and bipolarons

Magnetoelastic properties of multiferroic hexagonal ErMnO3

Unusual rotating magnetocaloric effect in the hexagonal ErMnO3 single crystal

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