Abstract
The effect of the partial substitution of Fe by Co and Mn on the structural and magnetic properties of Fe-Pd alloys has been investigated by means of calorimetric, magnetic and neutron diffraction measurements. The addition of Mn increases both the reversible and irreversible MT temperatures whereas the addition of Co causes the opposite effect, which points out that that the compositional dependence of the transformation temperatures of the Fe-Pd alloys is not related to the Pd amount but to the e/a concentration. Furthermore, it is shown that the appearance of the BCT phase is directly related to the tetragonality of the FCT phase. On the other hand, the amount of FCT martensite that irreversibly transforms into the undesirable BCT phase is considerably reduced by both the Co and Mn doping. The substitution of Fe by Co seems to be especially interesting for magnetic field-induce strains applications since both the magnetic anisotropy and the saturation magnetization of the Fe-Pd FCT martensite are considerably increased with the Co addition.
Highlights
Ferromagnetic shape memory alloys (FSMA) are being widely studied and discussed along the last two decades because of the unique properties they show as a result of the combination of a thermoelastic Martensitic Transformation (MT) and a magnetic transition
It is found that the addition of Mn increases both the reversible and irreversible MT temperatures whereas the addition of Co causes the opposite effect, confirming the e/a ratio influence on the transformation temperatures
This correspondence follows from the fact that once the alloys were cooled down to 125K no peak was observed in the subsequent heating ramp, whereas a high temperature endothermic peak corresponding to the reverse face-centered tetragonal martensite (FCT)→face-centered cubic austenitic phase (FCC) appears if the alloys are cooled to temperatures just above the low temperature anomaly
Summary
Ferromagnetic shape memory alloys (FSMA) are being widely studied and discussed along the last two decades because of the unique properties they show as a result of the combination of a thermoelastic Martensitic Transformation (MT) and a magnetic transition. The Fe-Pd alloys with Pd content ranging from 29% to 32% undergo a thermoelastic MT from a face-centered cubic austenitic phase (FCC) to a face-centered tetragonal martensite (FCT), at a temperature strongly dependent on the Pd content [8, 9] (a reverse FCT→FCC transformation occurs on heating due to the thermoelastic character of the MT).
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