Extraordinary magnetoelasticity and lattice softening in bcc Fe-Ga alloys

Abstract

Extraordinary magnetostrictive behavior has been observed in Fe-Ga alloys with concentrations of Ga between 4% and 27%. λ 100 exhibits two peaks as a function of Ga content. At room temperature, λ 100 reaches a maximum of 265 ppm near 19% Ga and 235 ppm near 27% Ga. For compositions between 19% and 27%, λ 100 drops sharply to a minimum near 24% Ga and exhibits an anomalous temperature dependence, decreasing by as much as a factor of 2 at low temperatures. This unusual magnetostrictive behavior is interpreted on the basis of a single maximum in the magnetoelastic coupling |b 1 | of Fe with increasing amounts of nonmagnetic Ga, combined with a strongly temperature dependent elastic shear modulus (c 11 −c 12 ) which approaches zero near 27% Ga. λ 111 is significantly smaller in magnitude than λ 100 over this composition range, and has an abrupt change in sign from negative for low Ga concentrations to positive for a concentration of Ga near 21%. Extraordinary magnetostrictive behavior has been observed in Fe-Ga alloys with concentrations of Ga between 4% and 27%. 100 exhibits two peaks as a function of Ga content. At room temperature, 100 reaches a maximum of 265 ppm near 19% Ga and 235 ppm near 27% Ga. For compositions between 19% and 27%, 100 drops sharply to a minimum near 24% Ga and exhibits an anomalous temperature dependence, decreasing by as much as a factor of 2 at low temperatures. This unusual magnetostrictive behavior is interpreted on the basis of a single maximum in the magnetoelastic coupling ͉b 1 ͉ of Fe with increasing amounts of nonmagnetic Ga, combined with a strongly temperature dependent elastic shear modulus (c 11 Ϫc 12 ) which approaches zero near 27% Ga. 111 is significantly smaller in magnitude than 100 over this composition range, and has an abrupt change in sign from negative for low Ga concentrations to positive for a concentration of Ga near 21%.

Density functional theory study of Fe3Ga

“…[1][2][3][4][5] Particularly, high values of magnetostriction ͑400 ppm͒ are observed along the ͗100͘ direction for x = 0.19 and 0.28, and within this concentration range the magnetostriction has a minimum of about 250 ppm at x = 0.225, 6 which is still a very high value compared to the 20 ppm of pure iron. A detailed structural investigation of the phase relations in single crystals show a strong dependence of the magnetostriction on the Ga concentration and on the sample thermal history as well as on the state of the chemical ordering in these alloys.…”

“…A detailed structural investigation of the phase relations in single crystals show a strong dependence of the magnetostriction on the Ga concentration and on the sample thermal history as well as on the state of the chemical ordering in these alloys. 6 In slow cooled samples for 0.225 Ͻ x Ͻ 0.28 only the DO 3 phase is present and the magnetostriction increases monotonically with x; in quenched alloys for x = 0.25 is observed a phase mixture of A2, B2, and DO 3 phases and the magnetostriction is enhanced as compared to the slow cooled samples ͑with single phase DO 3 ͒. The mixture of A2 and DO 3 phases is most stable in the metastable bcc region of the Fe-Ga phase diagram where the maximum magnetostriction is detected.…”

Role of Nanoscale Precipitates on the Enhanced Magnetostriction of Heat-Treated Galfenol (Fe1−xGax) Alloys

“…Previous studies of Fe 1Àx Ga x alloys cooled (postgrowth) at 10 C= min have shown the presence of two anomalous peaks in the magnetostriction. The first peak at x % 0:19 has been attributed to an increase in the magnetoelastic coupling, resulting from the formation of short-range ordered (SRO) Ga pairs along the [100] axis of the A2 structure [5], and the second at x % 0:27 to a softening of the shear modulus c 0 ¼ ðc 11 -c 12 Þ=2 [6,7]. Of special note is the fact that both 3 100 =2 and the presence of a two-phase region (A2 þ DO 3 ) depend sensitively on thermal history; this suggests that the enhanced magnetostriction is due to an underlying heterogeneity rather than a conventional homogeneous ferromagnetic phase.…”

Magnetostrictive and magnetoelectric behavior of Fe–20at.% Ga∕Pb(Zr,Ti)O3 laminates

“…Recently, a number of investigations have focused on Fe-Ga ͑Galfenol͒ alloys due to the combination of its high mechanical strength, good ductility, relatively large ͑3/2͒ 100 values, low saturation fields, high blocking stress, and low cost. [2][3][4][5][6][7] Galfenol has potential applications in acoustic projectors, acoustic sensors, and actuators. 8,9 Magnetoelectric materials have been very interesting since early Swiss 10 and Russian 11 work, and have recently had a renaissance ͑now commonly called multiferroic͒ in Nature, Science, Phys.…”