We report an infrared reflection spectroscopy study of La1/2Ca1/2MnO3 over a broad frequency range and temperature interval which covers the transitions from the high temperature paramagnetic to ferromagnetic and, upon further cooling, to antiferromagnetic phase. The structural phase transition, accompanied by a ferromagnetic ordering at TC=234 K, leads to enrichment of the phonon spectrum. A charge ordered antiferromagnetic insulating ground state develops below the N\'eel transition temperature TN=163 K. This is evidenced by the formation of charge density waves and opening of a gap with the magnitude of 2Δ0 = (320 ± 15) cm−1 in the excitation spectrum. Several of the infrared active phonons are found to exhibit anomalous frequency softening. The experimental data suggest coexistence of ferromagnetic and antiferromangetic phases at low temperatures.
@article{arxiv.cond-mat/0408157,
title = {Charge and Lattice Dynamics of Ordered State in La$_{1/2}$Ca$_{1/2}$MnO$_3$: Infrared Reflection Spectroscopy Study},
author = {A. P. Litvinchuk and M. N. Iliev and M. Pissas and C. W. Chu},
journal= {arXiv preprint arXiv:cond-mat/0408157},
year = {2009}
}