Discontinuity in heat capacity of Fe0.5Co0.5(110) alloy thin films

• Heat capacity as a function of temperature for 11, 15 and 19 atomic layers of FeCo thin films are determined.
• Curie temperature for Fe0.5Co0.5 thin films with 11, 15 and 19 are obtained.
• Bulk and thin films heat capacity of Fe0.5Co0.5 have a similar behavior.
• Discontinuity in heat capacity of thin films are similar to to bulk Fe0.5Co0.5.

In this work we calculate heat capacity of alloy thin films of FeCo on the surface of the plane (110), using three parameters, the concentration x(i), the lattice long range order parameter t(i) and the magnetic order parameter σ(i), being i the number of layers of the thin film. The formulations reported by Hill [1] in the context of small particles and Valenta's model [2] can be applied to the film structure when we treat a thin film as a system divided into subsystems equivalent to two-dimensional parallel layers. The FeCo bulk alloy is completely homogeneous while a thin film have spatial discontinuities in their surfaces. We consider three ferromagnetic thin films formed by 11, 15 and 19 layers in the Helmholtz's free energy, which is minimized applying their first partial derivatives with respect to chemical composition, long range order parameter and magnetic order parameter. We calculate internal energy and heat capacity as a function of temperature and we verify that have two jumps as are reported in literature for the bulk; there are many results of bulk or surface effects of FeCo, but no enough results about ferromagnetic FeCo thin films and this fact does this work interesting.