Competing exchanges and spin–phonon coupling in Eu_1−xR_xMnO₃(R=Y, Lu)

Abstract

This work is focused on the phase diagrams and physical properties of Y-doped and Lu-doped EuMnO3. The differences in the corresponding phase boundaries in the (x,T) phase diagram could be overcome by considering a scaling of the Y 3+ and Lu 3+ concentrations to the tolerance factor. This outcome evidences that the tolerance factor is in fact a more reliable representative of the lattice deformation induced by doping. The normalization of the phase boundaries using the tolerance factor corroborates previous theoretical outcomes regarding the key role of competitive FM and AFM exchanges in determining the phase diagrams of manganite perovskites. Though, significant differences in the nature and number of phases at low temperatures and concentrations could not be explained by just considering the normalization to the tolerance factor. The vertical phase boundary observed just for Lu-doped EuMnO3, close to 10%Lu, is understood considering a low temperature Peierls-type spinphonon coupling, which stabilizes the AFM4 phase in Lu-doped EuMnO3.

Dzyaloshinskii–Moriya nature of ferroelectric ordering in magnetoelectric Gd1−xYxMnO3 system

“…[36][37][38] This result has been pointed out as a clear evidence for the spin-phonon coupling in those rare-earth manganites. 9,13,39 The change of frequency of the optical phonons are a consequence of structural rearrangements induced by the magnetic order, which change the activation energy. So, the change of activation energy at well-defined temperatures evidenced in this work, which depend on the Y-concentration, points to changes on the energy barriers, due to magnetic spin rearrangements at T*.…”

Average and Local Crystal Structures of Multiferroic Eu1−xYxMnO3 (x = 0.2 and 0.4)

“…[ 4 ] Furthermore, as the ionic radii of Eu 3+ and Y 3+ are relatively different, the spatial variation of local distortions around R sites is expected in Eu 1− x Y x MnO 3 . [ 12 ] Significant magnetoelastic coupling [ 14,15 ] and strong spin‐phonon coupling [ 13,16–18 ] have been observed at the magnetic phase transitions in this system. Thus, the structural properties are of particularly importance in this system.…”

Unconventional spin-phonon coupling via the Dzyaloshinskii–Moriya interaction

“…A large number of studies have focused on 3d and 4d TMOs [17][18][19][20][21][22][23][24][25][26][27][28][29] where the SPC may be explained in terms of dynamic modulation of the IE interaction. RMnO 3 (R: rare-earth site ion), one of the widely investigated 3d TMOs, shows strong SPC phenomena which is closely linked with multiferroicity.…”

“…RMnO 3 (R: rare-earth site ion), one of the widely investigated 3d TMOs, shows strong SPC phenomena which is closely linked with multiferroicity. [17][18][19][20][21][22][23] Geometrically frustrated TMOs are also known to have strong SPC. [24][25][26][27] For example, in 3d ACr 2 O 4 (A: Cd, Zn), the coupling leads to spin-driven Jahn-Teller effects which relieve the magnetic frustration.…”

“…27,28 All of these SPC phenomena have been well explained by the dynamic modulation of the IE interaction. [17][18][19][20][21][22][23][24][25][26][27][28][29] The H spin in Eq. (1) indicates that other magnetic interactions could also induce SPC, but such possibilities have not been investigated to date.…”