MAGNETIC AND TRANSPORT-PROPERTIES OF NONEQUILIBRIUM EU-FE THIN-FILMS

We synthesized nonequilibrium EuxFe1-x (x = 0-0.95) alloy thin films b y coevaporation and studied their structural, magnetic and transport p roperties using x-ray diffraction (XRD), Mossbauer spectroscopy, a SQU ID and a DC four-probe method. The XRD and Mossbauer spectroscopy sugg ested that Fe atoms supersaturate in the bcc-Eu phase up to approximat ely 30 at.% Fe. On the other hand, these methods gave no indication of an extension in the solubility limit of Eu in the bcc-Fe phase. These nonequilibrium films possess the following properties: in the Fe-rich side, they exhibit a ferrimagnetic behaviour characterized by compens ation temperatures at which magnetization is nonzero. In the Eu-rich s ide, the magnetization curve at 4.2 K exhibits a small, irreversible k ink at about 8 T. At the same applied field, the magnetoresistance rat io (MR) changes irreversibly from positive to negative values, while s ubsequent runs yield only reversible, decreasing MR curves. These obse rvations on Eu-rich films suggest that the dissolved Fe atoms disturb the long-range helical order of the Eu spins, and that the spin struct ure changes irreversibly at about 8 T. At present, it remains unclear whether the above magnetic and transport behaviours are caused by the magnetic moments of Fe or simply by a structural disorder.