Paramagnetic collective electronic mode and low temperature hybrid modes in the far infrared dynamics of orthorhombic NdMnO₃
| Autor: | Massa, Néstor Emilio, Campo, Leire del, De Sousa Meneses, Domingos, Echegut, Patrick, Martínez-Lope, María Jesús, Alonso, José Antonio |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2013 |
| Předmět: | |
| Zdroj: | SEDICI (UNLP) Universidad Nacional de La Plata instacron:UNLP |
| Popis: | 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 D¹⁶2h-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. Facultad de Ciencias Exactas Centro de Química Inorgánica |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|