Magnetic phases in thin films of Ni–Fe(Co)–Ga ferromagnetic shape memory alloy

1 µ m-thick polycrystalline thin films of the ferromagnetic shape memory alloy, Ni_49.7Fe_17.4Co_4.2Ga_28.7 (at.%), were sputter-deposited on MgO(0 0 1) substrates heated at 773 K. The films' structure, magnetic properties and transformation behavior have been characterized. They exhibit both forward and reverse martensitic transformations at 218 K and 232 K, respectively. Ferromagnetic resonance and x-ray diffraction measurements discerned three ferromagnetic phases: cubic L2₁-ordered austenite, tetragonal martensite and disordered cubic γ -phase. The latter phase showed a unique spin-waves resonance spectrum, enabling estimation of the value of the exchange stiffness constant equal to A  =  0.7  ×  10⁻⁶ erg cm⁻¹. (paper)