Magneto-optical study of the spin-polarized electronic states in multiferroicTbMnO3

Abstract

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 . DOI: 10.1103/PhysRevB.77.193105 PACS number͑s͒: 75.47.Lx, 75.25.ϩz, 75.50.Ee, 77.22.Ej Multiferroic materials exhibit phases with simultaneous magnetic and ferroelectric properties. The close coupling of the magnetization and the electric polarization in multiferroics makes these materials excellent candidates for demonstrating giant magnetoelectrical behavior, 1,2 in which large magnetic and electric responses can be induced with weak electric and magnetic fields, respectively. 3,4 Spectral generalized magneto-optical ellipsometry ͑SGME͒ is an ideal technique for studying the interplay between electric and magnetic properties in multiferroic systems, as it probes both the diagonal xx and off-diagonal xy components of the dielectric tensor. 5 Multiferroicity in TbMnO 3 is induced by spin-charge coupling. Below the Néel temperature T N = 46 K, the wavelength of the incommensurate spin density decreases with decreasing temperature down to the ferroelectric transition at T F = 29 K. In the absence of a magnetic field, this spin-density modulation gets locked in at T F . Below T F , the inversion symmetry of the lattice is broken by the bc-cycloidal arrangement of the spins, inducing a ferroelectric polarization along the c axis while the antiferromagnetic ordering along the b axis persists. 3,4,6 Here, we study the coupling between spin and charge degrees of freedom in multiferroic TbMnO 3 by examining the temperature-dependent dielectric responses xx and xy , which are the diagonal and off-diagonal components of the dielectric tensor. The magnetization of a material breaks the symmetry between left and right circularly polarized ͑LCP and RCP͒ light. While 2xx is proportional to the sum of absorptions of LCP and RCP light, 1xy is proportional to the difference. 7 Consequently, a complete magneto-optical characterization of 2xx and 1xy in a magnetic material provides detailed information regarding the coupling between the material's electronic and magnetic properties.The temperature-dependent ellipsometry was done with a custom-made setup by using an extended Sentech SE850 spectral ellipsometer inside a He flow cryostat. The cryostat has stress-free mounted windows and maintains a base pressure of about 3 ϫ 10 −8 mbar at room temperature. 8 Standard ellipsometry was performed for temperatures from 10 to 470 K in the spectral range from 0.5 to 5.5 eV. In SGME, on...

Interplay ofp−dandd−dcharge transfer transitions in rare-earth perovskite manganites

“…13,14). A similar interpretation of spectral features near 2 eV observed in multiferroic TbMnO 3 was reported very recently by Bastjan et al 15 . Many researchers [11][12][13]16,17 pointed to a fine sub-peak structure of the low-energy 2 eV band.…”

Magnetic order dynamics in optically excited multiferroicTbMnO3

“…Using the fast-CCD camera (fCCD) [18], we measured the (0q0) diffraction peak in the in-plane scattering geometry as a function of relative delay between collinear propagating x-ray pulses (π-polarized; 100 fs FWHM) and 800 nm (1.55 eV) pump pulses (~120 fs pulse duration; 118 μm 1/e 2 radius; ppolarized). Figure 2(a) shows how the diffraction peak intensity varies with time for absorbed pump fluences ranging from 2.6 to 18.4 mJ/cm 2 , where we have accounted for the reflectivity using dielectric function data from Bastjan et al [21]. As no fast signal components were observed, here we show data binned into one picosecond time-steps.…”

“…In general the manganites show two prominent, broad features in the imaginary part of the dielectric function in the ultraviolet to near infrared spectral range [21,22]. At higher energies there is a strong increase typically attributed to charge transfer transitions from O 2p Mn 3d levels, creating locally an Mn 2+ excited state.…”

Directly probing spin dynamics in insulating antiferromagnets using ultrashort terahertz pulses

“…The THz probe and optical pump pulses were both linearly polarized along the a-axis and collinear. The absorption length for the optical pulse is only ∼200 nm [20], while the THz absorption length is closer to the entire crystal thickness, depending on the frequency and temperature (Fig. 1); the optical absorption thus determines the effective crystal length for our OPTP measurements.…”