Magnetooptics of magnetic-dipole transitions in the rare-earth paramagnetic garnets

Abstract

8571 Observed optical and magnetooptical spectra of rare earth (RE) ions in crystals are associated mainly with electric dipole (ED) transitions [1-3], although contributions from magnetic dipole (MD) transitions to the Faraday rotation have been found in some RE garnet crystals in the infrared (IR) spectral range [4][5][6]. The theory for MD transitions is well established for the LS coupling scheme and has been used to explain the features observed in the optical spectra of RE compounds [7][8][9]. At the same time, Kittel et al.[10] and Chetkin et al. [5] have examined some inter esting aspects regarding the application of this theory for an explanation of the Faraday rotation features in crystals of paramagnetic garnets YbAG and HoAG [5, 6] and europium ethylsulphate [10]. These authors have shown that in the magnetooptical spectra of these paramagnets, there is a wavelength independent gyro magnetic Faraday effect that is determined by the non diagonal component μ xy of the magnetic permeability tensor [4-6, 10].A quantum mechanical description of the Faraday effect in paramagnets has been carried out in [5] that shows that if J is a "good" quantum number and the frequency ω of the light wave is considerably larger 1 The article is published in the original. µ than the frequencies of all the magnetooptically active MD transitions within the ground multiplet (i.e., tran sitions following the MD selection rules, ΔL = 0, ΔS = 0, ΔJ = 0, and Δm = ±1) including relaxation frequencies, then the corresponding expression for the gyromagnetic rotation (per unit of length), can be written as [4][5][6] ,where is the average index of refraction of the crys tal, β = e/2mc, M is the magnetization, and g Jj is the Lande' factor of the magnetoactive ions in j th sublat tice.At the same time, according to [10], at low temper ature the Faraday rotation observed in the spectra of Eu 3+ ions is caused by Van Vleck "mixing" of the wavefunctions of the ground state |J 0 = 0, M 0 = 0〉 with the first excited state |J 1 = 1, M 1 = 0〉 [11], and also by the Zeeman splitting of the states |J 1 = 1, M 1 = ±1〉. In this case, as the electromagnetic wave frequencies ω are considerably larger than the resonance frequencies of the MD transitions between the neighboring mul ( ) 2 m F J j j j n g M c π β α = ∑ Abstract-The Faraday effect (FE) of the rare earth (RE) paramagnetic garnet crystals associated with mag netic dipole (MD) transitions has been investigated theoretically over a wide temperature range 80 to 300 K. Over this temperature range, the "gyromagnetic" Verdet constant of the Eu 3 Ga 5 O 12 (EuGG) is not a lin ear function of the magnetic susceptibility χ measured along the [111] axis. We find that the nontrivial char acter of the temperature dependence of the MD Verdet constant is associated with the presence of a con tribution to the Faraday rotation of the Van Vleck "mixing" by an external magnetic field of the Eu 3+ elec tronic states. The optical absorption and magnetic circular dichroism (MCD) of Eu 3+ ion in EuGG at 85 K fo...

Structural features and magnetic behavior of nanocrystalline powders of terbium oxide prepared by the thermal decomposition of terbium acetate in air

“…Note here that earlier measured [18] values of Θ for terbium oxides with compositions from TbO 2 down to TbO 1 …”

“…Terbium oxides find their wide use in many diverse scientific and technological applications [1], [2], [3], [4], such as optical, ceramic, and chemical ones. In optics these compounds have been utilized, for example, by TV manufacturers because Tb 3+ ions are among the most common CRT phosphors [5].…”

Magnetooptics of the luminescent transitions in Tb3+:Gd3Ga5O12

“…According to Kramers theorem [1], in the D 2 crystalline environment symmetry for the RE 3+ ions with an even number of equivalent 4f-electrons (so-called non-Kramers ions), the (2J + 1) non-degenerate energy (Stark) levels appear in each isolated 2S+1 L J multiplet of the RE-ion in the garnet structure [1][2][3]. However, especially within the manifolds with large J, some of these Stark levels are nearly degenerate and form so-called ''quasi-doublet'' states [1,[3][4][5]9]. In this case, ''mixing'' of the wavefunctions of two closely spaced (1-3 cm À1 ) non-degenerate Stark sublevels by the external magnetic field H [3,5] can be a basic source for the appearance of magnetooptical effects arising in the non-Kramers RE ions [3,9].…”

“…The study of the emission spectra in an external magnetic field is suitable for detecting the crystal-field (Stark) levels of the ground and low-energy excited multiplet manifolds of the 4f n and 4f nÀ1 5d configurations of the trivalent non-Kramers ions [9][10][11]. Indeed, the magnetooptical spectra can help to resolve more complicated spectroscopic problems arising in the investigations of the emission spectra of gadolinium gallium garnet Gd 3 Ga 5 O 12 (GGG) doped by the small amount of RE 3+ .…”

“…However, especially within the manifolds with large J, some of these Stark levels are nearly degenerate and form so-called ''quasi-doublet'' states [1,[3][4][5]9]. In this case, ''mixing'' of the wavefunctions of two closely spaced (1-3 cm À1 ) non-degenerate Stark sublevels by the external magnetic field H [3,5] can be a basic source for the appearance of magnetooptical effects arising in the non-Kramers RE ions [3,9].…”