MAGNETIC AND STRUCTURAL-PROPERTIES OF AS-MILLED AND HEAT-TREATED BCC-FE70CU30 ALLOY

A ferromagnetic solid solution with a nominal atomic composition Fe70C u30 and a body-centered structure has been obtained by high-energy bal l milling. The decomposition of the system is monitored by X-ray diffr action (XRD), magnetic measurements and Mossbauer spectroscopy. Accord ing to XRD, for heating temperatures below 723 K there is only a bcc p hase in the material, while for heating temperatures above 723 K a new phase, with a fee structure, appears, suggesting that the solid solut ion has decomposed into bcc-Fe and fcc-Cu. However, the magnetic behav ior observed during the decomposition process indicates that this evol ution is more complex than the simple decomposition into the equilibri um phases. This behavior can be summarized in two points: (1) a decrea se in the magnetization at 5 K, and (2) drastic changes in the coerciv e field with the thermal treatment, soft magnetic behavior for the mat erial in the as-milled state, superparamagnetism for low heating tempe ratures and a hardening of the material heated to above 723 K, for whi ch the values of the coercive field at room temperature are several ti mes higher than those for the as-milled sample. The Mossbauer spectros copy performed at room temperature shows that for the heat-treated sam ples the Fe atoms are in two different phases: a ferromagnetic phase, which evolves to bcc-Fe, and a paramagnetic phase.