Thermal Generation of Spin Current and Magnon Propagation Length in Compensated Ferrimagnetic Gd₃Fe₅O₁₂ Thin Films

The magnon propagation length (MPL) is one of the crucial factors to govern spin transport in a magnetic material. Here, we determine MPL (
$\xi$
) in compensated ferrimagnetic Gd
₃
Fe
₅
O
₁₂
(GdIG) thin films at room temperature by investigating longitudinal spin Seebeck effect (LSSE) in Gd
₃
Ga
₅
O
₁₂
(GGG)/GdIG(
$t$
)/Pt (5 nm) heterostructures with different thicknesses (
$t$
) of the GdIG film. All films possess in-plane (IP) magnetic easy axis, and the compensation temperature shifts down to lower temperature with decreasing GdIG thickness. At room temperature, the LSSE signal is rather constant with thickness between
$t = 221$
and 89 nm, but drops significantly below
$t = 50$
nm. By fitting the thickness dependence of the LSSE voltage to a modified atomistic spin model considering the influence of saturation magnetization, we obtain
$\xi $
= 45 nm ± 8 nm for GdIG thin films at room temperature. The MPL of GdIG is much shorter than that of Y
₃
Fe
₅
O
₁₂
films (
$\xi $
~90–140 nm), but higher than that of Fe
₃
O
₄
films (
$\xi $
~20 nm). The obtained value of
$\xi $
explains the drop in the LSSE voltage in GdIG films when the film thickness is reduced below 50 nm, knowledge of which is also essential to the design of spincaloritronic devices based on GdIG films.