Phonons and hybrid modes in the high and low temperature far infrared dynamics of hexagonal TmMnO₃

Abstract

We report on temperature dependent TmMnO 3 far infrared emissivity and reflectivity spectra from 1910 K to 4 K. At the highest temperature the number of infrared bands is lower than that predicted for centrosymmetric P6 3 /mmc (D 6h 4 ) (Z=2) space group due high temperature anharmonicity and possible defect induced bitetrahedra misalignments. On cooling, at ~1600 ± 40 K, TmMnO 3 goes from non-polar to an antiferroelectric-ferroelectric polar phase reaching the ferroelectric onset at the ~700 K.

A long-range model with energy–spin coupling and critical properties of hexagonal antiferromagnetic manganites

“…For the samples YMnO 3 and TmMnO 3 , experimental values for two critical exponents (namely, α and β) are available. For YMnO 3 , experiments yielded α = −0.12 ± 0.01 [33] and β = 0.42 ± 0.03 [5], whereas for TmMnO 3 the estimates were α = −0.19 ± 0.01 [33] and β = 0.420 ± 0.001 [34]. It is important to note that both these critical exponents for both samples are reproducible by the present model by tuning only one parameter ρ in the theory.…”

“…Numerical simulations [37] yielded α = +0. 34 and β = 0.25 for the chiral XY and α = +0. 24 and β = 0.30 for the chiral Heisenberg models.…”

Spin-phonon coupling in the incommensurate magnetic ordered phase of orthorhombic TmMnO3

“…This structure can be described as layers of MnO 5 bipyramids separated by Tm 3+ layers [ 11 ]. Wang et al [ 12 ] studied the ferroelectric behavior of hexagonal TmMnO 3 (h -TMO), reporting a ferro-paraelectric phase transition around 621 K, whereas, Yen et al [ 13 ] observed a magnetic transition around 84 K. Later, Massa et al [ 14 ] con rmed the electric and magnetic transitions showing a ferroelectric-magnetic coupling in the magnetically ordered phase using far-infrared emissivity and re ectivity measurements.…”