mag·ne·to·stric·tion 
(măg-nē′tō-strĭkshən)
(măg-nē′tō-strĭkshən)n.
Deformation of a material, especially a ferromagnetic material, exposed to a magnetic field. Rapidly alternating magnetostriction causes the iron cores of transformers to hum or buzz.
[MAGNETO- + (CON)STRICTION.]
mag·ne′to·strictive adj.