Invented in 1914 by physicist Gustav Elmen at Bell Telephone Laboratories to inductively load transatlantic submarine telegraph cables, increasing their signaling speed fourfold.
Near 80% nickel and 20% iron in a face-centered cubic lattice (a ≈ 0.355 nm), magnetostriction and magnetocrystalline anisotropy both approach zero, yielding relative permeability around 100,000 and very low coercivity.
Its up to 5% anisotropic magnetoresistance (AMR) and low hysteresis loss make permalloy a staple of thin-film magnetic recording read heads, transformer laminations, and magnetic shielding.