Interaction of Trace Rare‐Earth Dopants and Nanoheterogeneities Induces Giant Magnetostriction in Fe‐Ga Alloys

Abstract

The discovery of a tenfold increase in magnetostriction of Fe by alloying nonmagnetic Ga was a breakthrough in magnetostrictive materials. The large magnetostriction is attributed to tetragonal nanoheterogeneities dispersed in the bcc matrix. A further remarkable fivefold increase is achieved by trace rare earth doping (<1 at%) up to a value of ≈1500 ppm, more than 50 times that of pure iron. However, it remains a mystery why trace rare earth dopants can induce such giant magnetostriction. Here, it is found that interaction of rare earth dopants with the nanoheterogeneities produces the giant magnetostriction, through a combination of experimental studies, firstprinciples calculation and phase field simulations. The dopants tend to enter the nanoheterogeneities, increasing their distortion thereby creating a larger tetragonal distortion of the matrix as well as increased magnetocrystalline anisotropy. A mesoscopic model is developed using phase field simulation showing that the bulk tetragonal distortion arises mainly from those nanoheterogeneities with fixed Ga-Ga pairs parallel to the applied magnetic field. Increased tetragonal distortion of the doped nanoheterogeneities leads to further distortion of the matrix. The results deepen the understanding of heterogeneous magnetostriction, and will guide the search for new magnetic materials with giant magnetostriction.

Giant Enhancement of Magnetostrictive Response in Directionally-Solidified Fe83Ga17Erx Compounds

“…In related compounds, namely Tb- and Ce-doped directionally solidified FeGa systems, an increase in magnetostriction has been linked to improved grain orientation and morphology [23,24]. Based on experimental and computational studies conducted by He et al, it is surmised that the giant magnetostriction in rare-earth doped FeGa alloys may be ascribed to the presence of nano-heterogeneties in the samples [28]. The dopants tend to enter the nano-heterogeneities, creating a larger tetragonal distortion of the matrix, as well as increased magnetocrystalline anisotropy.…”

“…The dopants tend to enter the nano-heterogeneities, creating a larger tetragonal distortion of the matrix, as well as increased magnetocrystalline anisotropy. A mesoscopic model developed using phase field simulations shows that the bulk tetragonal distortion arises mainly from those nano-heterogeneities with fixed Ga–Ga pairs parallel to the applied magnetic field [28]. …”

“…While tiny amounts of small interstitial atoms (C, B or N) have a slight but favorable effect on the magnetostriction of FeGa (particularly at high atomic compositions of Ga) [18,19]. More recent studies indicate that the magnetostriction of this compound can be significantly increased by adding small amounts of rare-earth elements ranging from La to Lu [20,21,22,23,24,25,26,27,28]. A phenomenological model based on the rare-earth crystal field interaction, proposed by He et al, suggests that the best trace dopants are the light rare earths, Ce and Pr (up to 0.2 at.% doping), which give a transverse magnetostriction of up to 800 ppm [24].…”

Room temperature giant magnetostriction in single-crystal nickel nanowires

“…However, extended X-ray absorption fine-structure (XAFS) analysis of the second coordination shell around Ga provides clear evidence for the presence of one highly strained (+4%) Ga-Ga pair and five Ga-Fe pairs among six crystallographically equivalent <100> atomic pairs 2 . This result supports recent total energy calculations, in which the large magnetostriction in these alloys is attributed to the strain caused by the rotation of the magnetization in the vicinity of such defects.…”

“…Significant interest in magnetostrictive nanostructures dates back to the mid-1970s 1 , with many reports on thin films, multilayers, and superlattices exhibiting large magnetostriction [2][3][4] . In these planar systems, a large magnetostrictive strain on the order of 0.1% was observed for textured Co 0.75 Fe 0.25 thin films 5 , while Tb 0.3 Dy 0.7 Fe 2 bulk crystals showed magnetostriction λ 111 values of 0.16% 6,7 .…”