Nanodispersed<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">D</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>-phase nanostructures observed in magnetostrictive Fe–19% Ga Galfenol alloys

Bhattacharyya, Somnath; Jinschek, Joerg R.; Khachaturyan, A. G.; Cao, Hu; Li, Jiefang; Viehland, Dwight

doi:10.1103/physrevb.77.104107

Cited by 83 publications

(42 citation statements)

References 17 publications

(41 reference statements)

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“…These data (i) eliminate the possibility of B2 ordering as the origin of the (100) Bragg peak, as the ð1=2 1=2 1=2Þ superlattice reflection occurs only for the DO 3 structure, and (ii) demonstrate that the size of coherent DO 3 nanoprecipitates increases dramatically on approaching the A2-DO 3 boundary. Further, the linewidth determined from the ð1=2 1=2 1=2Þ diffuse peak for x ¼ 19 corresponds to a correlation length of 1.1 nm, which is consistent with results from the HRTEM study [9]. Two interesting differences between the (100) and ð1=2 1=2 1=2Þ diffuse peaks are apparent for Fe 0:81 Ga 0:19 .…”

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confidence: 78%

“…bcc 0 þ DO 3 decomposition, followed by (ii) a diffusionless Bain strain that transforms the DO 3 nanoprecipitates into a face-centered tetragonal (fct) structure. Recently, nanometer-scale (<2 nm) DO 3 precipitates [9] have been identified in an A2 matrix of Fe 0:81 Ga 0:19 using high-resolution transmission electron microscopy (HRTEM), consistent with the theoretical prediction of step (i) in the transformational sequence. However, all prior structural investigations have shown that both the DO 3 and A2 phases are cubic.…”

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confidence: 48%

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

et al. 2009

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We report neutron diffuse scattering measurements on highly magnetostrictive Fe 1Àx Ga x alloys (0:14 < x < 0:20) with different thermal treatments. This diffuse scattering scales with magnetostriction and exhibits asymmetric peaks at the (100) and (300) reciprocal lattice positions that are consistent with the coexistence of short-range ordered, coherent nanometer-scale precipitates embedded in a long-range ordered, body-centered cubic matrix. A large peak splitting is observed at (300) for x ¼ 0:19, which indicates that the nanoprecipitates are not cubic and have a large elastic strain. This implies a structural origin for the enhanced magnetostriction. DOI: 10.1103/PhysRevLett.102.127201 PACS numbers: 75.80.+q, 61.05.fg, 64.70.Nd, 75.50.Bb Mechanically strong and malleable Galfenol alloys (Fe 1Àx Ga x ) exhibit enhanced and extremely large magnetostriction coefficients along [100] of up to 3 100 =2 ¼ 400 ppm at low saturation fields [1,2]. The addition of Ga into the body-centered cubic (bcc) -Fe phase is known to produce a diversity of crystal structures including chemically disordered bcc A2 (Fe), ordered bcc DO 3 (Fe 3 Ga), ordered bcc B 2 (FeGa), and face-centered cubic L1 2 (Fe 3 Ga) phases [3,4]. 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.A structurally heterogeneous model [8] has been proposed to explain the enhanced magnetostriction and elastic softening for such Fe 1Àx Ga x alloys. This model assumes that the heat treatment produces a structurally and chemically heterogeneous state consisting of coarseningresistant, nanometer-scale DO 3 precipitates within an A2 matrix. Theoretically, heterogeneity has been predicted to result from the following sequence of transformations: (i) bcc ! bcc 0 þ DO 3 decomposition, followed by (ii) a diffusionless Bain strain that transforms the DO 3 nanoprecipitates into a face-centered tetragonal (fct) structure. Recently, nanometer-scale (<2 nm) DO 3 precipitates [9] have been identified in an A2 matrix of Fe 0:81 Ga 0:19 using high-resolution transmission electron microscopy (HRTEM), consistent with the theoretical prediction of step (i) in the transformational sequence. However, all prior structural investigations have shown that both the DO 3 and A2 phases are cubic. There have been no reports of lower-symmetry phases, as predicted by step (ii) in the transformational sequence. This is a ke...

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confidence: 78%

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confidence: 48%

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

et al. 2009

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“…39). In a recent report, a significant amount of D0 3 nanoprecipitates dis persed in the host A2 matrix was observed in Fe-Ga samples, and the D0 3 nanoprecipitates are believed to have a significant role in the enhancement of the magnetostriction 40 . The interpretation is that coarsening resistant metastable martensitic clusters form, when D0 3 precipitates equilibrate by undergoing a displacive transition and it is these martensitic clusters that lead to magnetostriction.…”

Section: Discussionmentioning

confidence: 91%

Giant magnetostriction in annealed Co1−xFex thin-films

et al. 2011

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Chemical and structural heterogeneity and the resulting interaction of coexisting phases can lead to extraordinary behaviours in oxides, as observed in piezoelectric materials at morphotropic phase boundaries and relaxor ferroelectrics. However, such phenomena are rare in metallic alloys. Here we show that, by tuning the presence of structural heterogeneity in textured Co 1 − x Fe x thin films, effective magnetostriction λ eff as large as 260 p.p.m. can be achieved at lowsaturation field of ~10 mT. Assuming λ 100 is the dominant component, this number translates to an upper limit of magnetostriction of λ 100 ≈ 5λ eff > 1,000 p.p.m. microstructural analyses of Co 1 − x Fe x films indicate that maximal magnetostriction occurs at compositions near the (fcc + bcc)/bcc phase boundary and originates from precipitation of an equilibrium Co-rich fcc phase embedded in a Fe-rich bcc matrix. The results indicate that the recently proposed heterogeneous magnetostriction mechanism can be used to guide exploration of compounds with unusual magnetoelastic properties.

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“…Some theoretical and experimental works support the extrinsic origin of their magnetostrictive properties, based on the reorientation of tetragonal defects resulting from the process of transformation of the structure of the alloy from bcc to fcc such as with increasing metalloid concentration structures. [11][12][13] This model assumes that the alloy is heterogeneous, as experimentally recognized by electron microscopy 14 and neutron scattering. 15 On the other side, there are the rigid band models that consider that the magnetostriction of these alloys is intrinsic and derives from the specific electronic structure of the crystal.…”

Section: Introductionmentioning

confidence: 99%

Determination of the magnetostrictive atomic environments in FeCoB alloys

et al. 2012

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The atomic environments of Fe and Co involved in the magnetostriction effect in FeCoB alloys have been identified by differential extended x-ray fine structure (DiffEXAFS) spectroscopy. The study, done in amorphous and polycrystalline FeCoB films, demonstrates that the alloys are heterogeneous and that boron plays a crucial role in the origin of their magnetostrictive properties. The analysis of DiffEXAFS in the polycrystalline and amorphous alloys indicates that boron activates magnetostriction when entering as an impurity into octahedral interstitial sites of the Fe bcc lattice, causing its tetragonal distortion. Magnetostriction would be explained then by the relative change in volume when the tetragonal axis of the site is reoriented under an externally applied magnetic field. The experiment demonstrates the extreme sensitivity of DiffEXAFS to characterize magnetostrictive environments that are undetectable in their related EXAFS spectra.

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NanodispersedDO3-phase nanostructures observed in magnetostrictive Fe–19% Ga Galfenol alloys

Cited by 83 publications

References 17 publications

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

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

Giant magnetostriction in annealed Co1−xFex thin-films

Determination of the magnetostrictive atomic environments in FeCoB alloys

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