Synchrotron radiation-based far-infrared spectroscopic ellipsometer with full Mueller-matrix capability (original) (raw)

Magneto-optical study of the spin-polarized electronic states in multiferroic TbMnO3

Physical Review B, 2008

The magnetic and electronic properties of multiferroic TbMnO 3 in the paramagnetic, antiferromagnetic, sinusoidal, and spiral-spin phases were studied by spectral generalized magneto-optical ellipsometry. The measurements show a strong anisotropy of the dielectric tensor. A redistribution of spectral weight was observed in the diagonal components of the dielectric tensor for the temperature range from 110 to T N =46 K. In the off-diagonal elements, spectral generalized magneto-optical ellipsometry shows sensitivity to the antiferromagnetic and ferroelectric phase transitions at T N = 46 K and T F = 29 K, respectively, and a persistent signal up to 6T N .

Magnetic and Magnetoelectric Excitations in TbMnO3

Physical Review Letters, 2009

Magnetic and magnetoelectric excitations in the multiferroic TbMnO3 have been investigated at terahertz frequencies. Using different experimental geometries we can clearly separate the electroactive excitations (electromagnons) from the magneto-active modes, i.e. antiferromagnetic resonances (AFMR). Two AFMR resonances were found to coincide with electromagnons. This indicates that both excitations belong to the same mode and the electromagnons can be excited by magnetic ac-field as well. In external magnetic fields and at low temperatures distinct fine structure of the electromagnons appears. In spite of the 90 o rotation of the magnetic structure, the electromagnons are observable for electric ac-fields parallel to the a-axis only. Contrary to simple expectations, the response along the c-axis remains purely magnetic in nature.

Evidence for large electric polarization from collinear magnetism in TmMnO3

New Journal of Physics, 2009

There has been tremendous research activity in the field of magnetoelectric (ME) multiferroics after Kimura et al (2003 Nature 426 55) showed that antiferromagnetic and ferroelectric orders coexist in orthorhombically distorted perovskite TbMnO 3 and are strongly coupled. It is now generally accepted that ferroelectricity in TbMnO 3 is induced by magnetic long-range order that breaks the symmetry of the crystal and creates a polar axis (Kenzelmann et al 2005 Phys. Rev. Lett. 95 087206). One remaining key question is whether magnetic order can induce ferroelectric polarization that is as large as that of technologically useful materials. We show that ferroelectricity in orthorhombic (o) TmMnO 3 is induced by collinear magnetic order, and that the lower limit for its electric polarization is larger than in previously investigated orthorhombic heavy rare-earth manganites. The temperature dependence of the lattice constants provides further evidence of large spin-lattice coupling effects. Our experiments suggest that the ferroelectric polarization in the orthorhombic perovskites with

Magneto-optical investigation of spin polarisation of and

Journal of Magnetism and Magnetic Materials, 2005

ABSTRACT We investigate the ferromagnetic phase of thin epitaxial films of the CMR manganites La0.7Ca0.3MnO3La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3La0.7Sr0.3MnO3 by temperature-dependent spectral generalised magneto-optical ellipsometry (SGME). The phase transitions from a paramagnetic insulator to a ferromagnetic metal take place at TC≈265K and TC≈335K, respectively. The measurements covering a spectral range of 0.5–5 eV are performed in the temperature range of 25–425 K. SGME allows a complete magneto-optical characterisation consisting of the determination of the diagonal components ɛxxɛxx as well as the off-diagonal components ɛxyɛxy of the dielectric tensor within a single measurement. Upon cooling through the Curie temperature, we observe the development of a Drude-like free-carrier response in ɛxxɛxx, indicating the release of previously bound charges. Meanwhile, ɛxyɛxy exhibits a rising magneto-optical response. This reflects, via the increasing degree of spin polarisation of the bands involved in optical transitions, the emergence of ferromagnetism. We tentatively assign spectral features between 2.5 and 4.5 eV to transitions involving the Mn-d shell, especially the egeg and t2gt2g levels.

Circularly Polarized X Rays as a Probe of Noncollinear Magnetic Order in Multiferroic TbMnO3

Physical Review Letters, 2009

Nonresonant x-ray magnetic scattering has been used to study the magnetic structure of multiferroic TbMnO 3 in its ferroelectric phase. Circularly polarized x rays were combined with full polarization analysis of the scattered beam to reveal important new information on the magnetic structure of this canonical multiferroic. An applied electric field is shown to create essentially a single magnetic domain state in which the cycloidal order on the Mn sublattice rotates either clockwise or anticlockwise depending on the sign of the field. It is demonstrated how this technique provides sensitivity to the absolute sense of rotation of the Mn moments and to components of the ordering on the Tb sublattice and phase shifts that earlier neutron diffraction experiments could not resolve.

Electron Spin Resonance (ESR) and Microwave Absorption Studies in TbMnO$_3$Multiferroic Compound

IEEE Transactions on Magnetics, 2006

We report temperature dependent X-Band (9 5 GHz) Electron Spin Resonance (ESR) and microwave absorption measurements in a single crystal of TbMnO 3. A single Lorentzian ESR line with an isotropic g-value g 1 96 was observed for 120 K up to 600 K. The ESR signal is attributed to the Mn 3+ ions in a insulator environment. The temperature dependence of the ESR linewidth is investigated for the external field applied along the three crystallographic axes. For all direction the ESR linewidth show a strong broadening as the temperature decreases due to the presence of short range magnetic correlations. The microwave absorption around the ferroelectric transition lock 27 K was investigated using a special cavity with a TE 103 mode where the sample sits at the maximum microwave electric-field.

Magnetic excitations in a cycloidal magnet: the magnon spectrum of multiferroic TbMnO 3

Journal of Physics: Condensed Matter, 2008

The magnetic excitations in multiferroic TbMnO 3 have been investigated by inelastic scattering of polarized and unpolarized neutrons in the ferroelectric cycloidal and in the paraelectric collinear phase. The polarization analysis of the excitations at the incommensurate magnetic zone center allows one to determine the characters of three distinct modes. In particular we may identify those modes which may directly couple to the ferroelectric polarization. We find a rather complex magnon dispersion with branches split throughout the Brillouin zone, which should be a generic characteristic of elliptical cycloidal order.

Magnetic Excitations in Multiferroic TbMnO_{3}: Evidence for a Hybridized Soft Mode

Physical Review Letters, 2007

The magnetic excitations in multiferroic TbMnO 3 have been studied by inelastic neutron scattering in the spiral and sinusoidally ordered phases. At the incommensurate magnetic zone center of the spiral phase, we find three low-lying magnons whose character has been fully determined using neutronpolarization analysis. The excitation at the lowest energy is the sliding mode of the spiral, and two modes at 1.1 and 2.5 meV correspond to rotations of the spiral rotation plane. These latter modes are expected to couple to the electric polarization. The 2.5 meV mode is in perfect agreement with recent infraredspectroscopy data giving strong support to its interpretation as a hybridized phonon-magnon excitation.

Magnetoimpedance spectroscopy of epitaxial multiferroic thin films

Physical Review B, 2012

The detection of true magnetocapacitance (MC) as a manifestation of magnetoelectric coupling (MEC) in multiferroic materials is a nontrivial task, because pure magnetoresistance (MR) of an extrinsic Maxwell-Wagner-type dielectric relaxation can lead to changes in capacitance [G. Catalan, Appl. Phys. Lett. 88, 102902 (2006)]. In order to clarify such difficulties involved with dielectric spectroscopy on multiferroic materials, we have simulated the dielectric permittivity ε of two dielectric relaxations in terms of a series of one intrinsic film-type and one extrinsic Maxwell-Wagner-type relaxation. Such a series of two relaxations was represented in the frequency-(f -) and temperature-(T -) dependent notations ε vs f and ε vs T by a circuit model consisting in a series of two ideal resistor-capacitor (RC) elements. Such simulations enabled rationalizing experimental f -, T-, and magnetic field-(H -) dependent dielectric spectroscopy data from multiferroic epitaxial thin films of BiMnO 3 (BMO) and BiFeO 3 (BFO) grown on Nb-doped SrTiO 3 . Concomitantly, the deconvolution of intrinsic film and extrinsic Maxwell-Wagner relaxations in BMO and BFO films was achieved by fitting f -dependent dielectric data to an adequate equivalent circuit model. Analysis of the H -dependent data in the form of determining the H -dependent values of the equivalent circuit resistors and capacitors then yielded the deconvoluted MC and MR values for the separated intrinsic dielectric relaxations in BMO and BFO thin films. Substantial intrinsic MR effects up to 65% in BMO films below the magnetic transition (T C ≈ 100 K) and perceptible intrinsic MEC up to − 1.5% near T C were identified unambiguously.