Thickness dependence of magnetic properties in La-Co substituted strontium hexaferrite films with perpendicular anisotropy

The thickness dependence of magnetization reversal and coercivity behavior for La-Co substituted strontium hexaferrite (Sr-M) films was investigated. It is found that perpendicular anisotropy appears only when film thickness (t) is above 110 nm. With increasing t, perpendicular anisotropy energy (K-u perpendicular to) increases gradually to its maximum of 1.76 x 10(6) erg/cm(3) at t = 300 nm, but turns to decrease when t > 300 nm. Moreover, when t > 110 nm, those films exhibit domains pinning or Stoner-Wohlfarth reversal model, present large K-u perpendicular to values and a rapid increase in H-c perpendicular to. However, while t <= 110 nm, Sr-M films show nucleation model of magnetization reversal and perform low coercivity. The origin of the coercivity varying with thickness should be correlated with the grain size and preferred orientations in Sr-M films. (C) 2015 Elsevier B.V. All rights reserved.