Optical Spectrum of ${Cr}^{3 +}$ Pairs in LaAl $O_{3}$

1 November 1971

journal article
research article
Published by American Physical Society (APS) in Physical Review B

Vol. 4 (9), 2888-2905
https://doi.org/10.1103/physrevb.4.2888

Abstract

The optical spectrum and exchange splittings of the nearest-neighbor

{Cr}^{3 +}

pairs in LaAl

O_{3}

have been studied. The absorption and emission spectra of the

{}^{4}A_{2} {}^{4}A_{2} \leftrightarrow {}^{2}E {}^{4}A_{2}

pair transitions from 7200 to 7600 Å yield the ground-state exchange

- J^{ab} ({\vec{S}}^{a} \cdot {\vec{S}}^{b}) + j {({\vec{S}}^{a} \cdot {\vec{S}}^{b})}^{2}

with

J^{ab} = - 66.6

{cm}^{- 1}

and

j = - 0.76

{cm}^{- 1}

. The emission lines were studied as a function of uniaxial stress applied along the trigonal axis. The stress dependences of the pair lines are not very different from the single-ion shifts. The energy levels of the

{}^{2}E {}^{4}A_{2}

and

{}^{2}E {}^{2}E

pair states have also been determined. The latter corresponds to exciting both ions to the

{}^{2}E

state, and the absorption is in the ultraviolet at about twice the

{}^{2}E

single-ion energy. The excited-state splittings are compared with the values calculated from

H_{ex} = - Σ J_{ij} {\vec{S}}_{i} \cdot {\vec{s}}_{j}

, where the sums are over the electronic spins

{\vec{S}}_{i}

and

{\vec{S}}_{j}

of the

{Cr}^{3 +} t_{2 g}

orbitals and the

J_{ij}

are empirical parameters. For the

{}^{2}E {}^{4}A_{2}

levels we find that

J_{11} = - 531.1

{cm}^{- 1}

and

\frac{1}{2} (J_{12} + J_{21}) = 55.4

{cm}^{- 1}

are the dominant exchange parameters. The signs and relative magnitudes agree with Anderson's theory. The pair lines have electric dipole polarization, and the strongest transitions obey the selection rule

Δ S = 0

Δ M_{s} = 0

. The polarization agrees with the calculated selection rules of the exchange-induced spin-dependent dipole moment

P = Σ P_{ij} {\vec{S}}_{i} \cdot {\vec{S}}_{j}

Keywords

This publication has 25 references indexed in Scilit:

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Physical Review Letters, 1971
Exchange Interaction and Energy Transfer for $3 d^{3}$ Ions: ${}^{4}A_{2} - {}^{2}E$ Transition for KMg $F_{3}$ : $V^{2 +}$
Physical Review B, 1970
Optical and Electron-Spin-Resonance Studies of Fourth-Nearest-Neighbor Chromium Ion Pairs in Ruby
Physical Review B, 1969
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Physical Review B, 1969
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Cited by 58 articles

Optical Spectrum ofCr3+Pairs in LaAlO3

Abstract

Keywords

Optical Spectrum of ${Cr}^{3 +}$ Pairs in LaAl $O_{3}$