Paramagnetic Resonance Spectra of ${Fe}^{3 +}$ in ZnW $O_{4}$

The paramagnetic resonance spectra of

{Fe}^{3 +}

in ZnW

O_{4}

have been examined at millimeter and centimeter wavelengths. The spectra fit a conventional spin Hamiltonian (in susceptibility coordinates)

H = g β H \cdot S + {B_{2}}^{0} {O_{2}}^{0} + {B_{2}}^{2} {O_{2}}^{2} + {B_{4}}^{0} {O_{4}}^{0} + {B_{4}}^{2} {O_{4}}^{2} + {B_{4}}^{4} {O_{4}}^{4},

with

S = \frac{5}{2}

g = 2.0019

{B_{2}}^{0} = - 6.987

kMc/sec,

{B_{2}}^{2} = + 4.935

kMc/sec,

{B_{4}}^{0} = + 0.00326

kMc/sec,

{B_{4}}^{2} = - 0.00178

kMc/sec, and

{B_{4}}^{4} = - 0.0173

kMc/sec. The slight reduction in the

g

value from the free-ion value and the sign of

{B_{4}}^{4}

(which is positive in the distorted cubic axis system) are in agreement with the theoretical predictions of Watanabe. The hyperfine structure due to

{Fe}^{57}

could be observed in low-concentration, natural-abundance samples at 1.5°K. The hyperfine constant

| A_{z} |

was found to be 28.9±1.4 Mc/sec. A point-charge calculation of the axial crystalline-field parameter

{A_{2}}^{0}

yielded a positive value which suggests that the coefficient of the quadratic dependence of

{B_{2}}^{0}

{A_{2}}^{0}

is negative.

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Paramagnetic Resonance Spectra ofFe3+in ZnWO4