Electronic structures of hexagonalRMnO3(R=Gd, Tb, Dy, and Ho) thin films: Optical spectroscopy a

Abstract

We investigated the electronic structure of multiferroic hexagonal RMnO 3 (R = Gd, Tb, Dy, and Ho) thin films using both optical spectroscopy and first-principles calculations. One of the difficulties in explaining the electronic structures of hexagonal RMnO 3 is that they exist in nature with limited rare earth ions (i.e., R = Sc, Y, Ho -Lu), so a systematic study in terms of the different R ions has been lacking. Recently, our group succeeded in fabricating hexagonal RMnO 3 (R = Gd, Tb, and Dy) using the epitaxial stabilization technique [Adv. Mater. 18, 3125 (2006)]. Using artificially stabilized hexagonal RMnO 3 , we extended the optical spectroscopic studies on the hexagonal multiferroic manganite system. We observed two optical transitions located near 1.7 eV and 2.3 eV, in addition to the predominant absorption above 5 eV. With the help of first-principles calculations, we attribute the low-lying optical absorption peaks to inter-site transitions from the oxygen states hybridized strongly with different Mn orbital symmetries to the Mn 3d 3z 2 -r 2 state. As the ionic radius of the rare earth ion increased, the lowest peak showed a systematic increase in its peak position. We explained this systematic change in terms of a flattening of the MnO 5 triangular bipyramid.

Study of spin-ordering and spin-reorientation transitions in hexagonal manganites through Raman spectroscopy

“…The antiferromagnetic spin-ordering transition in the a - b plane of the Mn 3 +  spins occurs at Néel temperature ~70–130 K, depending on the rare earth ion333435. Including the antiparallel and parallel orientation of corresponding Mn 3 +  spins at z  = 0 and z  =  c /2 in the unit cell, there are a few different possible magnetic symmetries18.…”

Spin exchange interactions in hexagonal manganites RMnO3 (R = Tb, Dy, Ho, Er) epitaxial thin films

“…1-3 Multiferroic hexagonal manganites have attracted much interest because of their promising properties and potential applications. [4][5][6][7][8][9][10][11][12][13][14] Hexagonal RMnO 3 (R ¼ rare earth) have ferroelectric properties with fairly large remnant polarization and quite high Curie temperature (T C ), typically above 590 K. Hexagonal RMnO 3 also exhibit antiferromagnetic behaviors, with Néel temperature (T N ) of 70-120 K. Below T N , the antiferromagnetic exchange between Mn moments leads to their 120 ordering in the basal a-b plane. 15,16 The in-plane (a-b plane) antiferromagnetic exchange is the dominant spin exchange interaction, while the inter-plane exchange interaction is about two orders of magnitude weaker, 17,18 which often be considered negligible.…”

“…In order to measure the Raman peak wavenumbers precisely, all the spectra have been calibrated in the frequency by using a standard neon source just before and after the measurements. Figure 2 shows the Raman spectra of the hexagonal RMnO 3 (R ¼ Tb, Dy, Ho, Er) thin films obtained at 13 the crossed polarization. The strong broad peak $760 cm À1 is originated from four-magnon scattering, the weak broad peak $950 cm À1 is from six-magnon scattering; the strong narrow peak $685 cm À1 is assigned to A 1 phonon, the weak narrow peak $640 cm À1 is assigned to E 1 phonon.…”

Magnetic and optical properties of multiferroic GdMnO3 nanoparticles

“…The electronic structure of the manganites has a close relationship with their crystal structure, specially the distance between Mn and O atoms. [13][14][15][16] It is well known that the nanosized materials may exhibit unique electrical, magnetic, and optical properties far different from those of their bulk counterparts because of low dimensionality and quantum confinement effect. 17 In this work, we study the magnetic and optical properties of GdMnO 3 nanoparticles.…”