Thermal effect on the coercivity of ultrathin NiFe films

The temperature dependence of the coercivity of ultrathin NiFe films was measured by a SQUID in the temperature range from 5 to 300 K. The change in coercivity with temperature was much greater for thinner films than for thicker ones. A domain wall motion model is proposed to explain the experimental results. It is concluded that the intrinsic coercivity increases rapidly with decreasing thickness, especially in the range of several nm, and that the low coercivity observed for very thin films at room temperature is ascribed primarily to the thermal effect.