Raman Scattering in CMR Manganites

Granado, E.; Moreno, N. O.; Garcı́a, Ana; Sanjurjo, J. A.; Rettori, C.; Torriani, Iris Concepcion Linares de; Oseroff, S. B.; Neumeier, J. J.; McClellan, K. J.; Cheong, S.‐W.; Tokura, Y.

doi:10.4028/www.scientific.net/msf.302-303.134

Cited by 20 publications

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“…8,9 Indeed, Granado et al 10,11 obtained an evidence of the spin-phonon coupling by analyzing the softening of the Raman active 610 cm −1 and 490 cm −1 modes of LMO below T N . Since the orbital ordering temperature ͑T oo ͒ of LMO is 780 K, a simultaneous spin-orbital-phonon coupling is expected below T N ͑140 K͒.…”

Section: Divalentmentioning

confidence: 97%

“…The Raman scattering was done using 180°back-scattering geometry in the temperature range between 5 and 300 K. In order to avoid heating of the sample, the incident laser power was kept below 15 mW focused in a diameter of ϳ50 m. To minimize surface decomposition effects, all the spectra were taken on fresh broken surfaces, exposed to the air for a few minutes before being measured. 10 In the orthorhombic LMO with Pnma symmetry, the two most intense bands that appear at 490 and 610 cm −1 undergo a softening below T N . 10 By considering the nearest neighbors of the Mn 3+ ion and using the molecular field approximation, 11 one can show that the frequency modulation due to a spin-phonon interaction is directly proportional to the square of M͑T͒, as manifested in Eq.…”

Section: Divalentmentioning

confidence: 99%

“…10 In the orthorhombic LMO with Pnma symmetry, the two most intense bands that appear at 490 and 610 cm −1 undergo a softening below T N . 10 By considering the nearest neighbors of the Mn 3+ ion and using the molecular field approximation, 11 one can show that the frequency modulation due to a spin-phonon interaction is directly proportional to the square of M͑T͒, as manifested in Eq. ͑1͒…”

Section: Divalentmentioning

confidence: 99%

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Orbital-spin-phonon coupling in Jahn-Teller-distortedLaMnO3: Softening of the 490 and610cm−1Raman-active m

Park

Jang

2007

Phys. Rev. B

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The spin-phonon coupling model that excludes a possible orbital-spin-phonon ͑OSP͒ coupling does not adequately explain the softening behavior of the two most intense Raman bands of LaMnO 3 , the parent compound of "colossal" magnetoresistivity. To quantitatively interpret the softening behavior of these two Raman bands at 490 and 610 cm −1 , we have derived theoretical expressions for the phonon softening ͑⌬ N ͒ that take account of a simultaneous OSP coupling. The present analysis successfully explains the softening behavior of these two Raman modes and indicates that a simultaneous OSP coupling is present below the Néel temperature, T N . The estimated effective force constant ͑k osp ͒ of the OSP coupling is approximately 70 dynes/ cm, which is an order of magnitude smaller than that of the spin-phonon coupling ͑k s-ph ͒. Divalentcation-modified lanthanum manganites ͑LaMnO 3 ; LMO͒ that display "colossal" magnetoresistivity have rekindled our interests in these strongly correlated electronic oxides. The subtle interplay between spin, charge, orbital, and lattice degrees of freedom is the most prominent feature in this class of perovskites and is believed to be the key to understanding their extraordinary transport and magnetic properties. [1][2][3][4] The study of the parent compound LMO is a useful starting point to a consistent understanding of this complex interplay between various degrees of freedom.In the perovskite orthorhombic LMO ͑space group Pnma͒, all of the Mn ions are trivalent with four electrons in 3d orbitals. Among these four electrons, one electron occupies one of the doubly degenerate e g orbitals, and thus the ion has both spin and orbital degrees of freedom. 5,6 Below 780 K, the orbital degree of freedom is spontaneously frozen by the real-space C-type ordering of the e g orbitals accompanied by a Jahn-Teller-type lattice distortion of the MnO 6 octahedra. 6,7 In addition, the spin ordering appears below T N Ϸ 140 K, where spins, due to the Hund's exchange coupling, 6 are aligned ferromagnetically in the basal plane and antiferromagnetically along the perpendicular direction ͑A-type antiferromagnetic ordering͒.Because the Raman scattering technique is highly sensitive to local symmetry change, this method has been applied to the study of the lattice modulation of spins, orbitals, and electrons ͑polarons͒ in manganites. 8,9 Indeed, Granado et al. 10,11 obtained an evidence of the spin-phonon coupling by analyzing the softening of the Raman active 610 cm −1 and 490 cm −1 modes of LMO below T N . Since the orbital ordering temperature ͑T oo ͒ of LMO is 780 K, a simultaneous spin-orbital-phonon coupling is expected below T N ͑140 K͒. In spite of this expectation, little progress has been made along this line. Here we report an interesting indication of a simultaneous coupling of orbital, spin, and lattice degrees of freedom by carefully examining the softening behavior of Raman active phonons.Orthorhombic LMO ͑Pnma͒ polycrystalline samples used in the present Raman and magnetization measurement...

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Section: Divalentmentioning

confidence: 97%

Section: Divalentmentioning

confidence: 99%

Section: Divalentmentioning

confidence: 99%

See 1 more Smart Citation

Orbital-spin-phonon coupling in Jahn-Teller-distortedLaMnO3: Softening of the 490 and610cm−1Raman-active m

Park

Jang

2007

Phys. Rev. B

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“…5͑b͔͒ and at low temperature. 33 ͒ Therefore, the width and intensity of the stretching modes are a measure of the amplitude of the dynamical JT distortions, which correlates to the activation energy for polaronic conduction.…”

Section: Paramagnetic Phases Of Low To Optimally Doped Manganitesmentioning

confidence: 99%

“…4, the disappearance of the high-frequency stretching modes in the La 1Ϫx Ca x MnO 3 series. Granado et al 7 report, in La 1Ϫx Mn 1Ϫx O 3 the softening of the high-frequency phonons across Tc and explained it to be caused by a strong spinphonon coupling. On the other hand, the Raman background can give information on the electronic excitations.…”

Section: Introductionmentioning

confidence: 96%

Raman phonons as a probe of disorder, fluctuations, and local structure in doped and undoped orthorhombic and rhombohedral manganites

et al. 2002

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We present a rationalization of the Raman spectra of orthorhombic and rhombohedral, stoichiometric and doped, manganese perovskites. In particular, we study RMnO 3 (RϭLa, Pr, Nd, Tb, Ho, Er, Y, and Ca͒ and the different phases of Ca-or Sr-doped RMnO 3 compounds as well as cation deficient RMnO 3 . The spectra of manganites can be understood as combinations of two kinds of spectra corresponding to two structural configurations of MnO 6 octahedra and independently of the average structure obtained by diffraction techniques. One type of spectra corresponds to the orthorhombic Pbnm space group for octahedra with cooperative or dynamic Jahn-Teller distortions, with stretching modes as the main features and whose frequencies correlate to Mn-O distances. The other spectrum is associated to regular but tilted octahedra whose modes can be described in the rhombohedral R3c structure, where only bending and tilt modes are observed. The main peaks of compounds with regular MnO 6 octahedra, such as CaMnO 3 , highly Ca-doped LaMnO 3 , or the metallic phases of Ca-or Sr-doped LaMnO 3 , are bending and tilt MnO 6 octahedra modes which correlate to R-O(1) bonds and Mn-O-Mn angles, respectively. In low and optimally doped manganites, the intensity and width of the broad bands are related to the amplitude of the dynamic fluctuations produced by polaron hopping in the paramagnetic insulating regime. The activation energy, which is proportional to the polaron binding energy, is the measure of this amplitude. This study permits to detect and confirm the coexistence, in several compounds, of a paramagnetic matrix with lattice polaron together with regions without dynamic or static octahedron distortions, identical to the ferromagnetic metallic phase. We show that Raman spectroscopy is an excellent tool to obtain information on the local structure of the different microphases or macrophases present simultaneously in many manganites.

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Room Temperature Spin‐Phonon Coupling in Cr₂O₃ Nanocrystals

Testa‐Anta

Majcherkiewicz

et al. 2023

Adv Funct Materials

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In this study, nanocrystals of antiferromagnetic Cr2O3 are shown via Raman spectroscopy to display peculiar lattice dynamics in terms of phonon softening and the occurrence of an exceptionally strong spin‐phonon coupling. This effect, which is observed to persist well above the onset of the antiferromagnetic ordering temperature, is ascribed to locally correlated spin fluctuations due to the modulation of the magnetic exchange interactions as the chromium atoms oscillate about their equilibrium position. It is found that the spin‐phonon coupling strength is governed by the competing antiferromagnetic and ferromagnetic interactions, where changes in the surface spin configuration can also play a crucial role. Overall, this work proves the size dependence of the interplay between the crystalline and magnetic structures in 3D antiferromagnets varying the surface‐to‐volume ratio and helps establish the fundamentals for a spin‐phonon coupling engineering at the nanoscale via a simple route in a very stable and easy to synthesize material. More importantly, it demonstrates the possibility of coupling phononic excitations with the magnetization dynamics at room temperature, offering a highly prospective nanomaterial for the design of novel magnonic devices.

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Raman Scattering in CMR Manganites

Cited by 20 publications

References 0 publications

Orbital-spin-phonon coupling in Jahn-Teller-distortedLaMnO3: Softening of the 490 and610cm−1Raman-active m

Orbital-spin-phonon coupling in Jahn-Teller-distortedLaMnO3: Softening of the 490 and610cm−1Raman-active m

Raman phonons as a probe of disorder, fluctuations, and local structure in doped and undoped orthorhombic and rhombohedral manganites

Room Temperature Spin‐Phonon Coupling in Cr₂O₃ Nanocrystals

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Raman Scattering in CMR Manganites

Cited by 20 publications

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Orbital-spin-phonon coupling in Jahn-Teller-distortedLaMnO3: Softening of the 490 and610cm−1Raman-active m

Orbital-spin-phonon coupling in Jahn-Teller-distortedLaMnO3: Softening of the 490 and610cm−1Raman-active m

Raman phonons as a probe of disorder, fluctuations, and local structure in doped and undoped orthorhombic and rhombohedral manganites

Room Temperature Spin‐Phonon Coupling in Cr2O3 Nanocrystals

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Product

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Room Temperature Spin‐Phonon Coupling in Cr₂O₃ Nanocrystals