Zeeman Effect of No-PhononA2g4−T2g4Transition ofCr3+in TiO2

The site symmetry of

{Cr}^{3 +}

in Ti

O_{2}

D_{2 h}

which splits the cubic

(O_{h}) {}^{4}T_{2 g}

state into

{}^{4}B_{1 g}

{}^{4}B_{2 g}

, and

{}^{4}B_{3 g}

. Spin-orbit interaction further splits these states into six Kramers doublets all of symmetry

Γ_{5}^{+}

. Previous optical work on Ti

O_{2}

{Cr}^{3 +}

established the lowest-lying sharp lines at 12 685 and 12 732

{cm}^{- 1}

as no-phonon lines of magnetic dipole character. It proposed these lines as due to transitions between the

{}^{4}A_{2 g}

ground state and two of the above six states. The present report extends this work by a Zeeman study, in emission, at 4 K of the line at 12 685

{cm}^{- 1}

. The results are: The Zeeman splitting of this line identifies the excited state of this transition as the

M_{s} = \pm \frac{3}{2}

spin-orbit component of an orbital state consisting of

77 % {}^{4}B_{2 g}

17 % {}^{4}B_{1 g}

, and

6 % {}^{4}B_{3 g}

with an effective

g = 1.73

. Furthermore, the line at 12 732

{cm}^{- 1}

is identified as the

M_{s} = \pm \frac{1}{2}

spin-orbit component by its effect in second order in the magnetic field on the Zeeman pattern of the line at 12 685

{cm}^{- 1}

. For the excited state the spin is quantized along the

x

direction of the magnetic axes while for the ground state it is quantized along the

z

direction. The reason for spin quantization along the

x

axis is discussed.

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