Fe Ga Single Crystals Research Articles

Tetragonal dipole dominated Zener relaxation in BCC-structured Fe-17at.%Ga single crystals

The stress-induced reorientation of the low-symmetry defects due to substitution atom pairs can give rise to an internal friction peak (Zener relaxation) and the first-nearest-neighbor substitutional atom pairs are plainly considered as the dominant contribution. Here, the Zener relaxation in the body-centered cubic (BCC) FeGa single crystals with different orientations was investigated, which against intuition originates primarily from the stress-induced reorientation of the second-nearest-neighbor Ga-Ga atom pairs. This Ga-Ga atom pair configuration is prevalent at high temperatures as directly observed by high-temperature in situ electron microscopy experiments. This phenomenon establishes non-ambiguously a direct correlation between Zener relaxation strengths and magnetostrictive properties. In addition, it was found that the diffusion activation energy of Ga atoms in FeGa single crystals is significantly lower than that in other iron-based alloys, suggesting that this value is closer to the actual diffusion activation energy of Ga atoms in FeGa alloys. These findings offer valuable insights into the study of short-range ordering in BCC alloys and the exploration of their functional properties.

Ultra-high anisotropic magneto-mechanical damping in Fe-18at.%Ga single crystals

An ultra-high anisotropic magneto-mechanical hysteresis-type damping (MMHD) with temperature and frequency insensitivity was found in Fe-18at.%Ga single crystals. The [111]-orientated Fe-Ga single crystal exhibits a damping value up to 0.13 (Q−1, equivalent to a special damping capacity SDC of 0.82) in the wide temperature range of −100–150 °C, much higher than that of the conventional ferromagnetic high damping alloys (Fe-Cr/Al based alloys). For the [001]-orientated single crystal however, the MMHD value is almost zero despite the large magnetostrictive coefficient along [001] direction. Through magnetic domain analysis, it is demonstrated that MMHD originates from the stress-induced irreversible movement of 90° domain walls. The MMHD of Fe-Ga single crystals depends positively on the orientation factor, and the ultra-high relaxation strength is closely related to the magnetostriction in the [001] direction and the tetragonal magnetoelastic coupling constant.

Influence of Ga content and high temperature annealing on the short range order and magnetostriction of Fe–Ga single crystals

Large magnetostriction observed in Fe–Ga alloys makes them a very important class of alloys for use in a wide range of actuation and sensing applications. This study of quantitative measurements of short-range order (SRO) in a series of Fe–Ga alloys provides valuable insights into the correlations of magnetostrictive responses with an increase in the Ga concentration and annealing. A quantitative assessment of SRO in the first seven shells around an atom in as-grown and high-temperature annealed [001]-oriented Fe–Ga alloy single crystals with Ga contents in the range of 5–20 at. % was carried out using the diffuse peaks in the forbidden (100) peak region of the θ–2θ high-resolution x-ray diffraction pattern. The SRO parameter values obtained indicate that very little short-range ordering occurs in Fe–Ga alloys with low Ga concentrations and ordering is limited to the first few shells. With an increase in Ga content, SRO increases with ordering occurring out to further shells. High temperature annealing decreases SRO parameters to levels approaching random solid solution. The decrease in short-range ordering with high-temperature annealing correlates with the increase in magnetostriction and confirms the hypothesis that the difference in the extent of ordering is the source of the observed high sensitivity of magnetostriction to changes in thermal history.

The Anisotropy of $\Delta E$ Effect of Fe–Ga Single Crystal

An extended model based on the Jiles–Thoekle and Armstrong model is used to model the anisotropy of $\Delta E$ effect of the Fe–Ga single crystal. Some specific crystallographic directions which are [100], [110], [111], and [112] directions are selected to study the magnetomechanical behavior under magnetic field and stress loading. The strain–stress curves and Young’s modulus-stress curves are simulated. Two more cases of direction selection [ $\theta \in (0,\pi)$ , $\varphi = \pi $ /4, and $\theta = \pi $ /2, $\varphi \in (0,2\pi)$ ] are used to study the relationship between $\Delta E$ effect and crystallographic direction, which shows that the directions showing minimum saturated magnetostriction and maximum pure elastic modulus along the two routes have an abnormal change trend of the $\Delta E$ effect. The results show that the $\Delta E$ effect of the Fe–Ga single crystal has a high degree of anisotropy. Both the atomic packing density and the domain motion have great effect on the final magnetomechanical coupling behavior.

Evaluation of Tri-Axial Magnetostriction in Cube-Oriented Fe-Ga Single Crystal by Using X-Ray Diffraction Method

We carried out in situ tri-axial magnetostriction analysis for cube-oriented Fe-18%Ga single crystal by X-ray diffraction measurement under magnetic field. Periodic change in tri-axial magnetostriction with applied magnetic field direction was clearly observed. However, those values in [100] and [010] directions were not equivalent. Theoretical calculation of magnetostriction considering domain structure revealed this is caused by the non-equivalent volume fraction of initial magnetic domains.

Peculiarities of high-temperature superelasticity in Ni–Fe–Ga single crystals in compression

The high-temperature superelasticity and temperature dependence of the yield stress of 14M and L10 martensite in [001]-oriented single crystals of Ni54Fe19Ga27 (at %) in compression alloy have been studied. As the temperature increases, the sequence of stress-induced martensitic transformations (MTs) changes from L21–14M to L21–L10. The yield stress of L10 martensite weakly depends on the temperature and is 1.7 times lower than that of 14M martensite. The temperature interval of superelasticity in [001]-oriented single crystals of Ni54Fe19Ga27 under compression is determined by the growth of critical stresses with increasing temperature, the coefficient of strain-hardening, and the yield stress of L10 martensite.

Magnetostriction of a Fe83Ga17 single crystal slightly doped with Tb

A novel strategy of sub-rapid directional solidification is developed for preparing doped FeGa single crystals. Crystals of nominal composition Fe83Ga17Tbx (x=0, 0.05) have been grown with [100] preferred orientation at a high growth rate of 3000mm/h. Using this method, trace amounts of normally-insoluble Tb can be incorporated into the A2 Fe83Ga17 matrix. A large magnetostriction (λ100) of 310ppm is achieved in the [100] oriented Fe83Ga17Tb0.05 single crystal, ~50% higher than that of a similar undoped crystal.

Magnetic domain characterisation of high magnetic field treated FeGa single crystal

Previous research has shown that stress annealing and magnetic field annealing can build uniaxial anisotropy into FeGa alloy to enhance saturation magnetostriction without preload. In this paper, we focus on the possibility of inducing uniaxial anisotropy in Fe81Ga19 single crystal by high magnetic treatment. The single crystal sample was grown by the Bridgman method and cut into an 8×5×5 mm cuboid with (001) planes determined by Laue backscattering. Both maze-like out of plane domains and true magnetic domains were obtained with magnetic force microscopy (MFM). The results indicate that magnetic domains were well aligned with the treating magnetic field. A reliable disparity of uniaxial anisotropy has been proved with the domain and domain wall width change in MFM patterns.

Anomalous Hall effect in epitaxially grown ferromagnetic FeGa/Fe3Ga hybrid structure: Evidence of spin carrier polarized by clusters

The anomalous Hall resistance relative with magnetic anisotropy of clusters Fe3Ga in Fe3Ga/Fe-Ga hybrid structural epitaxial was reported. The out-of-plane magnetic anisotropy was obtained for Fe3Ga/Fe-Ga hybrid structure, while in-plane magnetic anisotropy is shown in the single Fe-Ga phase epitaxial on GaAs(001). The observation of trend of saturation Hall resistance in Fe3Ga/Fe-Ga hybrid structural is compared with the Fe-Ga single crystal, which is solid evidence for spin polarization by local magnetic clusters.

Effect of Ga concentration on twinning pseudoelasticity in Fe–Ga single crystals

The effect of Ga concentration on the twinning pseudoelasticity in Fe–Ga single crystals with 20.0–24.4 at%Ga was examined. In Fe–20.0 to 24.4Ga (at%) single crystals, 2.2T-type pseudo-twins with {1 1 2} twin plane were formed during compression at low temperatures, especially at 93 K. The energy of the pseudo-twins was so high that the twins disappeared during unloading, resulting in the twinning pseudoelasticity. At 93 K, the amount of strain recovery caused by the twinning pseudoelasticity increased with increasing Ga concentration depending on the energy of the pseudo-twins. On the other hand, Fe–23.0Ga and Fe–24.4Ga single crystals with the D03 structure exhibited pseudoelasticity even at room temperature, which is based on reversible motion of 1/4[1 1 1] superpartial dislocations dragging antiphase boundaries. At 20.0 at%Ga, the twinning deformation was predominant at and below 173 K while large strain recovery due to the twinning pseudoelasticity at 24.4 at%Ga was observed only at 93 K. It is also noted that the stress–strain hysteresis at 93 K was greater at 24.4 at%Ga than at 23.0 at%Ga, which was closely related to a lattice distortion accompanying the pseudo-twin formation.

Effect of cooling rate on magnetoelasticity and short-range order in Fe–Ga alloys

For Fe–Ga single crystals, faster cooling rates achieved by metallic quench and ice-water quench extended the tetragonal magnetostriction constant, (3/2) λ 100 , to higher Ga contents than reported previously. The maximum magnetostriction measured was 420 ppm at a composition of 21.4 at.% Ga. Using these faster cooling rates, the formation of short-range order (SRO) was obviously suppressed in A2 single phase, while this change in SRO did not significantly affect (3/2) λ 100 .

Short range ordering in Fe–Ge and Fe–Ga single crystals

We report on the nature of short range ordering (SRO) in slow cooled (100) and (111) Fe81.6Ga18.4 and Fe81Ge9 single crystals determined by x-ray θ-2θ scans. The SRO of the Ga atoms has at least some D03 character. In contrast Ge atoms only exhibit B2 chemical ordering symmetries in the short range order. It has been proposed that the D03 character in the SRO is important for the enhancement in magnetoelasticity in Fe-based alloys; however the presence of B2 character in Fe–Ge alloys suggest that the SRO is not of primary importance in increasing the magnetostriction.

Inter-martensitic transitions in Ni–Fe–Ga single crystals

The strain–temperature response of Ni–Fe–Ga single crystals underscores the role of the inter-martensitic transformation in creating intersecting heating and cooling segments; the separation of these segments occurs due to irreversibilities at high stresses and at high temperatures. An ultra-narrow tensile (1 °C) and compressive (<10 °C) thermal hysteresis are observed for the A ⇌ 10 M ⇌ 14 M case, accompanied by a small stress hysteresis (<30 MPa) in compressive and tensile stress–strain responses. The hysteresis levels increase and the intersecting segments disappear at high stresses and at high temperatures. This paper reports the use of a thermo-mechanical formulation to rationalize the role of inter-martensitic transformations. Plotting the transformation stress as a function of temperature indicates that inter-martensitic transformations enable a very wide pseudoelastic temperature range, as high as 425 °C. The measured Clausius–Clapeyron curve slope in compression (2.75 MPa °C −1) is eight times the tensile slope (0.36 MPa °C −1); the higher slope is attributed to the predominance of A ⇌ L1 0 at high temperatures.

Magneto-elastic interactions in Fe–Ga alloys

The elastic anisotropy of iron’s most common α-structure increases significantly when gallium is substituted for a fraction of the iron. Concurrently occurring, the tremendous boost in tetragonal magnetostriction [one order of magnitude above that of pure Fe, 3/2λ100(Fe81Ga19)=400 ppm] makes Fe–Ga alloys important for magnetoelastic applications. Measurements of the elastic tensor of Fe–Ga single crystals, with or without a magnetic field and within 4–300 K, were performed using the resonant ultrasound spectroscopy technique on 100-cut rectangular parallelepipeds. In the vicinity of 24% Ga an anomaly occurs in the magnetostriction as well as in the elastic moduli and in the magnitude of their ΔE-effect, in an apparent conspiracy to maintain the magnetoelastic energy-constants (b1,2) ‘‘normal.’’ [Work supported by ONR.]

Magnetocrystalline anisotropy and magnetostriction in ordered and disordered Fe–Ga single crystals

Abstract On the basis of our new equilibrium phase diagram, Fe 1− x Ga x ( x =0.24–0.25) single crystals with the A2, B2 and D0 3 structures have been prepared in order to investigate the magnetocrystalline anisotropies and magnetostrictions. The [1 1 0] direction was identified as a hard axis and the anisotropy coefficients were | K 2 |> K 1 >0, 0> K 2 in the A2 and B2 structures. Lowering the symmetry of the atomic arrangement, the magnetostriction of the [1 0 0] direction becomes larger. These results agree with qualitatively the theoretical calculations.