Showing posts with label T. Rõõm. Show all posts
Showing posts with label T. Rõõm. Show all posts

Friday, October 18, 2019

Abstract-Magnetoelectric spectroscopy of spin excitations in LiCoPO 4


V. Kocsis, S. Bordács, Y. Tokunaga, J. Viirok, L. Peedu, T. Rõõm, U. Nagel, Y. Taguchi, Y. Tokura, and I. Kézsmárki

Figure
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.100.155124

We have studied spin excitations in a single-domain crystal of antiferromagnetic LiCoPO4 by terahertz absorption spectroscopy. By analyzing the selection rules and comparing the strengths of the absorption peaks in the different antiferromagnetic domains, we found electromagnons and magnetoelectric (ME) spin resonances in addition to conventional magnetic dipole active spin-wave excitations. Using the sum rule for the ME susceptibility, we determined the contribution of the spin excitations to all the different off-diagonal elements of the static ME susceptibility tensor in zero and finite magnetic fields. We conclude that the ME spin resonances are responsible for the static ME response of the bulk when the magnetic field is along the x axis, and the symmetric part of the ME tensor with zero diagonal elements dominates over the antisymmetric components.
  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Figure

Monday, July 3, 2017

Abstract-Magnetic Excitations and Continuum of a Field-Induced Quantum Spin Liquid in α-RuCl3



We report on terahertz spectroscopy of quantum spin dynamics in α-RuCl3, a system proximate to the Kitaev honeycomb model, as a function of temperature and magnetic field. An extended magnetic continuum develops below the structural phase transition at Ts2=62K. With the onset of a long-range magnetic order at TN=6.5K, spectral weight is transferred to a well-defined magnetic excitation at ω1=2.48meV, which is accompanied by a higher-energy band at ω2=6.48meV. Both excitations soften in magnetic field, signaling a quantum phase transition at Bc=7T where we find a broad continuum dominating the dynamical response. Above Bc, the long-range order is suppressed, and on top of the continuum, various emergent magnetic excitations evolve. These excitations follow clear selection rules and exhibit distinct field dependencies, characterizing the dynamical properties of the field-induced quantum spin liquid.

Tuesday, January 5, 2016

Abstract-Unidirectional terahertz light absorption in the pyroelectric ferrimagnet CaBaCo4O7


S. BordácsV. KocsisY. TokunagaU. NagelT. RõõmY. TakahashiY. TaguchiY. Tokura

http://arxiv.org/abs/1601.00444

Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which is a type-I multiferroic compound with the largest magnetic-order induced ferroelectric polarization ({\Delta}P=17mC/m2) reported, so far. We observed two optical magnon branches: a solely electric dipole allowed one and a mixed magnetoelectric resonance. The entangled magnetization and polarization dynamics of the magnetoelectric resonance gives rise to unidirectional light absorption, i.e. that magnon mode absorbs the electromagnetic radiation for one propagation direction but not for the opposite direction. Our systematic study of the magnetic field and temperature dependence of magnon modes provides information about the energies and symmetries of spin excitations, which is required to develop a microscopic spin model of CaBaCo4O7.

Friday, January 1, 2016

Abstract-Unidirectional terahertz light absorption in the pyroelectric ferrimagnet CaBaCo4O7


S. Bordács, V. Kocsis, Y. Tokunaga, U. Nagel, T. Rõõm, Y. Takahashi, Y. Taguchi, and Y. Tokura
Phys. Rev. B 92, 214441 – Published 31 December 2015

ABSTRACT 

Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which is a type-I multiferroic compound with the largest magnetic-order induced ferroelectric polarization (ΔP=17 mC/m2) reported, so far. We observed two optical magnon branches: a solely electric dipole allowed one and a mixed magnetoelectric resonance. The entangled magnetization and polarization dynamics of the magnetoelectric resonance gives rise to unidirectional light absorption, i.e., that magnon mode absorbs the electromagnetic radiation for one propagation direction but not for the opposite direction. Our systematic study of the magnetic field and temperature dependence of magnon modes provides information about the energies and symmetries of spin excitations, which is required to develop a microscopic spin model of CaBaCo4O7.
  • Figure
  • Figure
  • Figure
  • Figure

Wednesday, December 16, 2015

Abstract-Unidirectional terahertz light absorption in the pyroelectric ferrimagnet CaBaCo4O7


S. Bordács, V. Kocsis, Y. Tokunaga, U. Nagel, T. Rõõm, Y. Takahashi, Y. Taguchi, and Y. Tokura

https://journals.aps.org/prb/accepted/87070Y68Wc51f14ff95a2790416e16664585554e4

Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which is a type-I multiferroic compound with the largest magnetic-order induced ferroelectric polarization (DP=17 mC/m2) reported, so far. We observed two optical magnon branches: a solely electric dipole allowed one and a mixed magnetoelectric resonance. The entangled magnetization and polarization dynamics of the magnetoelectric resonance gives rise to unidirectional light absorption, i.e. that magnon mode absorbs the electromagnetic radiation for one propagation direction but not for the opposite direction. Our systematic study of the magnetic field and temperature dependence of magnon modes provides information about the energies and symmetries of spin excitations, which is required to develop a microscopic spin model of CaBaCo4O7.

Monday, May 27, 2013

Abstract-Terahertz spectroscopy of spin waves in multiferroic BiFeO3 in high magnetic fields





We have studied the magnetic field dependence of far-infrared active magnetic modes in a single ferroelectric domain \BFO/ crystal at low temperature. The modes soften close to the critical field of 18.8\,T along the [001] (pseudocubic) axis, where the cycloidal structure changes to the homogeneous canted antiferromagnetic state and a new strong mode with linear field dependence appears that persists at least up to 31\,T. A microscopic model that includes two \DM/ interactions and easy-axis anisotropy describes closely both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. The good agreement of theory with experiment suggests that the proposed model provides the foundation for future technological applications of this multiferroic material.