Magnetic Reversal and Temperature Dependence of Magnetic Properties in Sm–(Co,Cu)/Fe Exchange Spring Multilayer Films

The magnetization reversal mechanism and temperature dependence of magnetic properties of Cr(50 nm)/[SmCo₆(9 nm)/Cu(x nm)/Fe(5 nm)/Cu(x nm)]₆/Cr(100 nm)/a-SiO₂ (x = 0-0.75) exchange spring multilayer films are reported. The initial curves and angular-dependent coercivities measurement indicate that the magnetization reversal mechanism of multilayer films is determined by domain-wall pinning. With lowering the temperature, the coercivities of multilayer films increase largely. By inserting Cu layer between the hard and soft layers can increase the coercivity of the multilayer films, especially at low temperatures. The hysteresis loops of the film with x = 0.75 annealed at 500°C measured from 10 to 400 K show all the single-phase behavior, although the film contains a large amount of soft phase (≈40 vol%), indicating the strong exchange coupling between the hard and soft phase and the extremely large nucleation field in the soft layers. With the decrease of temperature, the maximum energy product (BH)_max and remanence also increase. A large (BH)_max of about 37.4 MGOe is obtained at 10 K for the film with x = 0.75 annealed at 500°C. The recoiling curves as well as the irreversible change in magnetization -ΔM_irrev(H)/2M_r = [M_r - M_d(H)]/2M_r versus the reverse field H demonstrate the increase of the inhomogeneity and pinning in the hard layer at the low temperature as well as after the addition of Cu, therefore, an improved coercivity.