Magnetic behavior of cosputtered Fe-Zr amorphous thin films exhibiting perpendicular magnetic anisotropy

Excellent mechanical properties of amorphous or glassy metals along with the capability to fabricate sub-50-nm patterns promise their application as a futuristic material for production of various nano- or microelectromechanical systems. In addition to their applications, these materials pose a lot of challenges in understanding their fundamental properties because of their random structure and involvement of three or more different kinds of atoms. The amorphous Fe-Zr system which is reported to exhibit superconductivity, ferromagnetism, spin glass, and antiferromagnetism is an ideal system to understand. The controversial magnetic properties of this system are still a subject of debate. In the present paper we revisited Fe-Zr system and studied their detailed magnetic properties in the temperature range of 5--330 K. FeₓZr_100-x ($x=63$, 68, 76, 86, 92, and 93 at. %) thin films were deposited on silicon (100) substrate by a cosputtering technique. The Curie temperature (Tc) is shown to increase almost linearly with an increase in Fe concentration, but it decreases rapidly for the Fe-rich films. The films with x up to ~86 at. % have a strange shape of the hysteresis loop and are shown to exhibit perpendicular magnetic anisotropy with a stripe domain structure. Hysteresis loop shapes are correlated with the magnetic structure of the films, and provide an easy understanding of magnetic properties. It has been shown that the Fe-rich films are composed of antiferromagnetic Fe clusters which are embedded in the ferromagnetic amorphous FeZr.