Magnons and crystal-field transitions in hexagonalRMnO3(R= Er, Tm, Yb, Lu) single crystals

Abstract

Far-infrared optical transmission spectra of the antiferromagnetic resonances, or magnons, and crystal field transitions have been studied in hexagonal REMnO 3 (RE = Er, Tm, Yb, Lu) single crystals. The magnon and CF frequencies, their oscillator strengths, and effective g-factors have been measured using external magnetic fields up to 9 T in the temperature range between 1.5 K and 100 K. The magnon frequency increases systematically with a decrease of the RE ion radius.The magnetic ordering of RE ions (RE=Er, Tm, Yb) was observed at low temperatures T<3.5 K and in strong external magnetic fields.

Asymmetric Splitting of an Antiferromagnetic Resonance via Quartic Exchange Interactions in Multiferroic Hexagonal HoMnO3

“…We can ascertain the origin of this asymmetry by examining the temperature dependence of the g-factors (Figure 4(b)). The g-factors increase with decreasing temperature, a trend which is consistent with other hexagonal manganites [29]. However, In HMO we ob- serve a large renormalization of the g-factors at T Ho , with increases of ≈ 50% and 35% from 30K to T Ho in the right hand and left hand branches respectively.…”

“…revealing two modes which split symmetrically in field with g eff = g 2+4∆/9J (see Eq's 8-12 of Sec. III in the SI for derivation) [29]. Note that even for small anisotropy, g eff is approximately half the bare ionic value.…”

“…With exchange and anisotropy found to be J = 2.44 meV and ∆ = 0.38 meV respectively in HMO [23], one expects g eff = 0.97 from Equation 2. However, in actuality much larger g-factors are observed at low temperatures in hexagonal manganites [7,29]. This has been explained by introducing an additional Heisenberg exchange interaction which ferromagnetically couples R spins to the finite S z of the Mn AFR modes into Equation 1 [7].…”

Hexagonal Manganites—(RMnO3): Class (I) Multiferroics with Strong Coupling of Magnetism and Ferroelectricity

“…The phase diagram of ErMnO 3 at low temperatures is nearly as complex as that of HoMnO 3 due to the magnetic exchange between rare earth moments and manganese spins which also have been shown to affect the magnon spectra and crystal field transitions in optical experiments [188]. On the other hand, there is also evidence for strong spin lattice interactions as, for example, shown in the phonon hardening below [166].…”

Terahertz-frequency magnetoelectric effect in Ni-doped CaBaCo4O7

“…THz frequency range (1 THz ≈ 4 meV ≈ 33 cm −1 ) is usually home to spin excitations in antiferromagnets and low frequency optical phonons. Detailed investigations of spin excitations in high magnetic field provide the experimental basis for the construction of accurate microscopic magnetic Hamiltonians [7][8][9][10] . THz spectroscopy has also provided the observations of electromagnons [11][12][13][14][15][16][17][18] which are electric-dipole-active spin excitations that receive their electric-dipole activity via microscopic magnetoelectric interactions.…”