demagnetize the compass or maladjust it by concealing a large bar of steel or iron near to it.
"Simple Sabotage Field Manual"
Strategic Services
Also tell him to have Davis rig up a demagnetizer large enough to demagnetize the motors of a transport plane and bring it down here to fix up General Merton's ship.
"The Great Drought"
Sterner St. Paul Meek
Soft iron cores are not used in oscillation inductance coils and oscillation transformers for the reason that the frequency of the current is so high the iron would not have time to magnetize and demagnetize and so would not help along the mutual induction to any appreciable extent.
"The Radio Amateur's Hand Book"
A. Frederick Collins