Concentration and temperature dependence of the Faraday rotation of lead-substituted gadolinium iron garnet films at 633 nm

The Faraday rotation of epitaxial garnet films of composition Gd
3-x
Pb
x
Fe
5-y
M
y
O
12
with M = Ge
⁴⁺
, Sn
⁴⁺
and
x, y \leq 0.44
has-been investigated in the temperature range
4.2 K \leq T \leq T_{c}
at λ = 633 nm. The temperature variation of the rotation can be described in terms of temperature independent magneto-optical coefficients and the sublattice magnetizations which were deduced from the fit of the molecular field theory to the measured saturation magnetization. The large negative contribution to the rotation Δθ
F
/x
pb
²⁺
= - 11000 deg cm
^-1
at T = 295 K turned out to be assigned only to the divalent lead ions. From the wavelength dependence in the visible it is found that this contribution also depends on the site occupation of the ions compensating the Pb
²⁺
.