Invar effect in fcc-FeCusolid solutions

Abstract

Both Cu and Fe metals, with face-centered cubic (fcc) crystal structures, are nonmagnetic. However, the substitution of Cu atoms by Fe in the fcc-Cu lattice leads to the formation of a random solid solution and the appearance of ferromagnetic order, with a value of the magnetic moment per Fe atom in a fcc environment even above 2 B . This striking behavior is closely related to magnetovolume effects (Invar), which we have detected by means of lattice thermal expansion and magnetization measurements in FeCu alloys.

Structure and Magnetic Properties of Aerosol Nanoparticles of Fe and Its Alloys

“…In this context, the possibility of formation of FM fcc Fe at the interface of copper and iron was ignored. On the other hand, the fcc Fe apparently plays an important role in the Invar effect observed at the BM metastable fcc Fe 44 Cu 56 alloy [12]. The lattice parameter measured by neutron diffraction in the temperature range between 300 and 350 K remains almost unchanged.…”

“…So, Cu-rich alloys show a giant magnetoresistance effect which can be used to develop sensors [5,6,107]. Another interesting result is a discovery of Invar effect at metastable Fe 44 Cu 56 alloy having an fcc structure [12]. A sharp change of thermal expansion coefficient for this alloy • C allows one to use it as a temperature switch.…”

“…Upon heating the alloy above 350 K it undergoes the PM → FM transition. The two-state Weiss' model satisfactorily explains the behavior of the Invar Fe 44 Cu 56 alloy [12,133].…”

High-temperature induced ferromagnetism onγ−Feprecipitates in FeCu solid solutions

“…[19][20][21] In special conditions, large magnetovolume effects can be observed, giving rise to macroscopic Invar behavior. 22 By contrast, small amounts of ␥-Fe precipitates in a Cu matrix exhibit antiferromagnetic order below 70 K, with Fe ϳ 0.5 B at 0 K. 23 Because of the metastable nature of these materials, heating above 500 K produces a wellknown segregation process, 16,17 which is concluded around 800 K. Then, the system transforms into body centered cubic ͑bcc͒ and fcc phases ͑which are Fe-and Cu-rich phases, respectively͒ plus a small amount of another fcc ͑Fe-rich͒ or ␥-Fe phase. 24,25 Using magnetization measurements as well as Mössbauer spectroscopy at low temperature, an intense search for magnetic order in these isolated ␥-Fe precipitates has been performed.…”

Stress-induced large Curie temperature enhancement inFe64Ni36Invar alloy

“…3,16 Therefore, this effective temperature invariant thermal expansion can be exploited in a number of technological applications such as precision measurements for standards, large size cryogenic liquid containers, etc. 15,17 Furthermore, the Invar effect is not limited to being a property of only Fe-Ni alloys, but it is also found in many other crystalline three dimensional ͑3D͒ systems such as Fe-Pt, Pd 3 Fe, Fe 3 C, or Fe-Cu, [18][19][20][21][22] amorphous Fe alloys, [23][24][25] as well as intermetallic systems such as R-Fe ͑R = Rare Earth͒. 26,27 Hence, these alloys can be structurally ordered or disordered, ferromagnetic or antiferromagnetic.…”