Alperm (also alfenol or alfer) is a class of alloys comprising 83-90% of iron and 10-17% of aluminium.
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.
For this reason alperm can be used in higher frequency range.
The alloy was first synthesized and characterized by Japanese researchers H. Masumoto and Hideo Saito in 1939.