Alperm

Alperm (also alfenol or alfer) - a class of alloys comprising 83-90% of iron and 10-17% of aluminium. The most widely used composition is with 16% Al.

An alloy with 13% Al is also sometimes referred to as alfer. It exhibits large magnetostriction and it is used in magnetoelastic sensors. Later during the WW2, Japanese used the alloy with 12.7-12.9% aluminium as a replacement of nickel for the magnetostrictive transducers used in their Type 93 model 5, Type 3, and Simple naval sonars.