Effect of ion-implantation on magnetic switching fields of single-domain, magneto-optic elements

The effect of multiple B+ implantation on 109 μm square single-domain magneto-optic elements formed by chemical etching of Bi-doped Tm:YIG epitaxial films (
\sim 7 \mu
m) is investigated by measuring the external switching field H
sw
sw required to reverse the magnetization
\bar{M_{s}}
as a function of implant profile, dosage, and the angle θ between the field and the film normal. For low doses (< 0.15% strain), switching is determined by coherent rotation in the implanted layer; H
sw
decreases linearly (
\lambda_{111} = -5.5 \times 10^{-6,} \theta = 0\deg
) from H
k
. 4πM
s
= 3995 Oe to 566 Oe and H
sw
(θ) is the classic switching curve for a uniaxial anisotropy. For higher doses, H
sw
remains constant or increases slightly, and H
sw
(\theta) \propto (\cos\theta)^{-1}
, indicating that switching is limited by wall motion, and the force proportional to
\nablaH_{k}
at the implant/bulk interface. With annealing H
sw
increases for low dose as H
k
increases, and decreases for higher doses as
\nablaH_{k}
decreases. Measurements width three stain profiles intricate that more gradual strain transitions produce lower H
sw
due to decreased
\nablaH_{k}
.