Abnormal temperature dependence of the coercive field in FePt thin films

J.M. GUZMÁN; N. R. ÁLVAREZ; H.R.SALVA; M.VASQUEZ MANSILLA; J.GÓMEZ; A.BUTERA

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 347 p. 61 - 67

0304-8853

We have observed notable changes in the magnetic response of FePt thin films that we have attributed to a transition in the magnetic domain structure when the film thickness or the temperature is varied. The critical thickness for this transition depends on the Q-factor, Q = Kp/2PiMs2, so that a change in the domain structure is expected when changes in the perpendicular anisotropy, Kp , or the saturation magnetization, Ms, occur.At room temperature these samples have Q = 0.3, and a transition between planar tostripe-likedomainsoccursfora film thickness d = 30 nm. Due to the different thermal expansion of the FePt alloy and the Si substrate a reduction in Q is predicted when the temperature is lowered. From magnetization vs. field loops measured at different temperatures below T = 300K, we have effectively observed a change in the coercive field which can be associated to a transition from stripe-like to in-plane domains. The transition temperature range is broad,indicating a gradual variation between the two magnetic configurations, but changes systematically with film thickness, consistent with an interfacial induced stress. A model that includes the temperature dependence of the strain and the magnetization,predicts correctly the observation of a larger critical thickness at lower temperatures.