A Raman spectroscopy study on the half-doped single-layer manganite Pr0.5Ca1.5MnO4 has been performed in combination with x-ray diffraction, resistivity, magnetization, and specific heat measurements. The results provide insight into the underlying mechanisms of phenomena that arise from correlations between lattice, charge, orbital, and spin degrees of freedom. The appearance of a new Raman mode at 366 cm(-1), a visible jump in the resistivity, and a doubling of the unit cell signify the onset of charge/orbital ordering at 320 K. This transition is also marked by a sharp peak in the magnetic susceptibility and specific heat, suggesting strong spin-charge coupling. Our structural analysis suggests that the charge disproportionation below 320 K is small. Orbital fluctuations below 320 K are evidenced by the evolution with temperature of the Jahn-Teller Raman mode (situated at 533 cm(-1) at 320 K). A coincidence between the onset of two-dimensional short-range antiferromagnetic order at 215 K and anomalies in both the temperature dependence of the Jahn-Teller mode and the Mn-O bonding pattern in the ab plane indicate that the short-range magnetic order plays a role in stabilizing the orbital fluctuations. Below the Neel temperature of 127 K, the softening of both the 366 cm(-1) mode and an octahedral tilting mode at 214 cm(-1) mark the onset of three-dimensional antiferromagnetic ordering. The estimated spin-phonon coupling constants for these two modes are 2.6 and 6.8 cm(-1), respectively. This study highlights the remarkable coupling of charge, orbital, and spin degrees of freedom to the lattice in single-layer Pr0.5Ca1.5MnO4.
|Tijdschrift||Physical Review. B: Condensed Matter and Materials Physics|
|Nummer van het tijdschrift||20|
|Status||Published - 2-nov-2015|