Paramagnetic collective electronic mode and low temperature hybrid modes in the far infrared dynamics of orthorhombic NdMnO3
We report on the far- and mid-infrared reflectivity of NdMnO3 from 4 to 300 K. Two main features are distinguished in the infrared spectra: active phonons in agreement with expectations for the orthorhombic ${\mathrm{D}}_{2\mathrm{h}}^{1 6}$–Pbnm (Z = 4) space group remaining constant down to 4 K an...
| Autores: | , , , , , |
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| Formato: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2013 |
| País: | Argentina |
| Recursos: | Consejo Nacional de Investigaciones Científicas y Técnicas |
| Repositorio: | CONICET Digital (CONICET) |
| Idioma: | inglés |
| OAI Identifier: | oai:ri.conicet.gov.ar:11336/24493 |
| Acesso em linha: | http://hdl.handle.net/11336/24493 |
| Access Level: | acceso abierto |
| Palavra-chave: | Collective Excitation Far Infrared Multierroics Spin Waves https://purl.org/becyt/ford/1.3 https://purl.org/becyt/ford/1 |
| Resumo: | We report on the far- and mid-infrared reflectivity of NdMnO3 from 4 to 300 K. Two main features are distinguished in the infrared spectra: active phonons in agreement with expectations for the orthorhombic ${\mathrm{D}}_{2\mathrm{h}}^{1 6}$–Pbnm (Z = 4) space group remaining constant down to 4 K and a well defined collective excitation in the THz region due to eg electrons in a d-orbital fluctuating environment. We trace its origin to the NdMnO3 high-temperature orbital disordered intermediate phase not being totally dynamically quenched at lower temperatures. This results in minute orbital misalignments that translate into randomized non-static eg electrons within orbitals yielding a room-temperature collective excitation. Below TN ~ 78 K, electrons gradually localize, inducing long-range magnetic order as the THz band condenses into two modes that emerge pinned to the A-type antiferromagnetic order. They harden simultaneously down to 4 K, obeying power laws with TN as the critical temperature and exponents β ~ 0.25 and β ~ 0.53, as for a tri-critical point and Landau magnetic ordering, respectively. At 4 K they match known zone center spin wave modes. The power law dependence is concomitant with a second order transition in which spin modes modulate orbital instabilities in a magnetoelectric hybridized orbital–charge–spin–lattice scenario. We also found that phonon profiles also undergo strong changes at TN ~ 78 K due to magnetoelasticity. |
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