The magnetostriction of Invar alloys

The principles of the theory of a phase transition into a magnetically ordered state are formulated for Invar alloys and other similar inhomogeneous ferromagnets, for which the concept of a local Curie temperature distribution corresponding to the experimentally observed broadened temperature interval of the transition into the ferromagnetic state has existed for 10 years. A method is proposed for obtaining information about the local temperature distribution from experimental data on the change in the properties of magnets in response to a change in temperature. For iron-nickel-chromium alloys it is shown how to obtain the temperature dependence of the magnetostrictional susceptibility of the paraprocess from data on the magnetic contribution to the thermal expansion coefficient. This confirms the important role of the local Curie temperature distribution, and it also indicates a need for new analysis of experimental data on temperature-broadened magnetic ordering phase transitions. Zh. éksp. Teor. Fiz. 113, 213–227 (January 1998)     

Shape effect in the magnetostriction of ferromagnetic composite

The magnetostriction of composite consisting of a soft matrix, non-magnetic, randomly filled by ferromagnetic particles is measured. The measured elongation on cylinder-shaped samples displays shape dependence. A model based on the demagnetizing field and the effective Young’s modulus is provided. Both calculation and measurement show a positive magnetostriction with larger values as the samples are flatter. The model is derived to have the behavior of the elongation as a function of the filling factor. An expression of the optimal filling factor, providing a maximal strain, is also expressed.     

The extraordinary hall effect in dilute Pd based alloys

The extraordinary Hall effect has been measured for ferromagnetic alloys PdNi, PdCo, PdFe and Mn. In the low concentration region, different behaviour of PdNi and PdCo in comparison with PdFe and PdMn confirms the existence of local orbital moments of Ni and Co in Pd.     

Volume and shape magnetostriction of ferromagnetic invar type alloys

The volume and shape magnetostriction ω_V(H) and ω_S(H) of an Invar alloy and a technical constant-modulus alloy were measured with a strain gauge technique at room temperature. The considerable shape magnetostriction amounts to 0.1 of the volume effect. The itinerant model of ferromagnetism and Kanamori's formula for correlation effects is applied. The observed magnetostriction implies a deformation potential of about 0.3 eV.     

Microscopic approach to magnetostriction of dilute rare-earth alloys

The theory of magnetostriction, formulated previously by one of the authors, is partially extended to arbitrary crystal symmetry and compared with experimental results for $\text{Ag}$RE dilute alloys. The field dependence of the forced magnetostriction in the 〈001〉 direction of the single crystal sample is in general quite well reproduced by the theory.     

Magnetic anisotropy,magnetostriction and intermediate range order in Co-P alloys

Coercivity, magnetostriction and saturation field as a measure of magnetic ansitropy energy have been investigated in Co_100-xP_x with 5 ? x ? 26. According to their magnetization curves and coercivities crystalline alloys (5 ? x ? 11) contain hcp-inclusions whereas amorphous material (12 ? x ? 26) is magnetically soft. The saturation magnetization is mainly determined by the nearest neighbour shell but magnetostriction is also correlated with the further environment of the cobalt atoms. The abrupt breakdown of the value |λ_s| of the saturation magnetostriction with increasing phosphorus content of the crystalline alloys points to a growing structural disorder. λ_s of the amorphous material depends on the saturation magnetization alone (λ_s ≈ σ₀²) which decreases with increasing phosphorus content. The small value of λ_s suggests that angular correlations do not exceed the second coordination shell.     

Temperature dependence of forced volume magnetostriction in fcc Fe-Ni alloys

The forced volume magnetostriction of the fcc Fe-Ni Invar alloys has been measured in the temperature range from 77 to 900 K to elucidate the magnetovolume effect at finite temperatures. The temperature dependence of (θ ω/θ(H/M) is evaluated as well as (θ ω/θH), where ω is the volume expansion. These results are discussed using a phenomenological model for the magnetovolume effect which takes into account the contribution of the correlation between local magnetic moments.     

Saturation and forced volume magnetostriction of Fe-rich FeZr amorphous alloys

AC susceptibility, saturation and forced volume magnetostriction were studied on iron-rich zirconium amorphous alloys a-Fe_100-xZr_x (8 at% ≤ x ≤ 12 at%). The experimental results are discussed in relation to the re-entrant spin glass state. It is found that the transverse magnetostriction accompanies a remarkable magnetic aftereffect in the spin glass phase, and that the forced volume magnetostriction shows an apparent peak at the ferromagnet to spin glass transition where the ac susceptibility has a cusp.     

Mechanism of stress dependence of saturation magnetostriction in amorphous alloys

The phenomenological theory of stress dependence of saturation magnetostriction in amorphous alloys has been developed. Two models of magnetostriction have been considered: the pair-ordering model and the random anisotropy model. The stress dependent magnetostriction is shown to be related to microstructural parameters of amorphous alloys. It has been concluded that recently performed experiments have confirmed theoretical predictions.     

Giant forced volume magnetostriction of Fe-rich iron-cobalt-zirconium amorphous alloys

The forced volume magnetostriction has been measured as a function of composition and temperature in amorphous (Fe_1?xCo_x)₉₀Zr₁₀ alloys. The maximum value of $\text{δω}\text{δH}$ (T = 0 K), equal to 285 × 10^-10 Oe^-1, has been observed for Fe₉₀Zr₁₀ alloys. The effect of pressure on the magnetization σ₀ at T = 0 K was calculated from $\text{δω}\text{δH}$ data. The pressure dependence of the Curie temperature T_c and σ₀ behaves in a similar way as those observed for crystalline NiPd and NiRh alloys.     

Model of colossal magnetostriction in the martensite phase of Ni-Mn-Ga alloys

A model is proposed for describing the experimentally observed martensite and magnetic domain structures in Heusler ferromagnetic alloys Ni_2+x Mn_1?x Ga. On the basis of this model, the field dependences of magnetization and deformation of the alloys are calculated numerically and an expression for the maximum attainable strains induced by external magnetic fields in these alloys is derived. It is shown that for small values of the effective elastic modulus and demagnetizing factor of alloys, the strains induced by the magnetic field may attain maximum possible values of approximately 5%, which are determined by lattice distortions as a result of the martensite transition in fields of about 1 kOe.     

Localised surface segregation and martensite nucleation in noble metal based ternary alloys

A recent model connecting martensite nucleation with localised surface segregation phenomena is extended to dilute ternary alloys based on -CuZn and -AuCd. Experimental data about composition induced variations of the critical temperature for the onset of martensitic transformation are organised in a coherent fashion by the atomistic Valence Electron Localisation Degree variation model. An analysis of the surface segregation properties of the original and effective alloys involved in micro nucleation events of martensite is performed by a model relying upon charge transfer effects. It is concluded that martensite nucleation may be interpreted in terms of preferential, localised surface segregation events.Preliminary results of the research were presented at the Discussion Meeting on CuZnAl Martensite Shape Memory Alloys, 19–21 June 1984, Leuven, Belgium     

Saturation magnetization and magnetostriction of Ni3Mn alloys containing aluminum and copper

An experimental investigation was made into the influence of the addition of copper and aluminum on the saturation magnetization J_s and magnetostriction _s of the Ni₃Mn alloy. It is shown that the behavior of J_s and _s depends on the distribution of the atoms of the added element over the sites of the fcc lattice of the Ni₃Mn alloy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 29–33, February, 1981.We should like to thank A. I. Lotkov for the alloys made available for investigation.     

Shape memory and pseudoelasticity in metal nanowires

Structural reorientations in metallic fcc nanowires are controlled by a combination of size, thermal energy, and the type of defects formed during inelastic deformation. By utilizing atomistic simulations, we show that certain fcc nanowires can exhibit both shape memory and pseudoelastic behavior. We also show that the formation of defect-free twins, a process related to the material stacking fault energy, nanometer size scale, and surface stresses is the mechanism that controls the ability of fcc nanowires of different materials to show a reversible transition between two crystal orientations during loading and thus shape memory and pseudoelasticity.     

Hyperfine magnetic field on Pd in Pd-Fe alloys

The hyperfine field on Pd nuclei in Pd-Fe alloys has been studied using the integral perturbed angular correlation technique (IPAC). Results are given for samples with iron contents from 3 to 60 at.% Fe and the temperature dependence of the hyperfine field is studied for a sample with 10 at.% Fe.     

Short-range order in metal alloys

Research on Short-range order presently develops along many lines [1].Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 40–52, August, 1976.     

Low temperature magnetostriction and magnetization of RE x Y1−x Pd3-alloys

Low temperature magnetostriction and magnetization measurements are reported for the series of RE _x Y_1–x Pd₃ alloys and for some REPd₃ compounds. The magnetostriction per Rare Earth ion is nearly independent of concentration and conserves volume at low fields. In both the alloys and compounds with the heavy Rare Earths and with Nd the magnetostriction tends to saturate at high fields together with the magnetization. The saturated quadrupolar magnetostriction as extracted from these data via the Callen projection, is of order a few times 10^–3 per Rare Earth ion. Sign and magnitude of this quadrupole do not correlate with the Stevens factor. The results are discussed in terms of aspherical screening of the nuclear charge from the outer valence electrons by the intervening 4f charge distribution.Supported by Sonderforschungsbereich 125, Deutsche Forschungsgemeinschaft, FRG     

Theory of solid solubility for rare earth metal based alloys

Both parabola and ellipse separating schemes are used to study the solid solubilities for the binary alloy systems based on the 13 rare earth metals. It has been found that the soluble elements can be separated from the insoluble ones by a parabolyy ₁=a?bx ₁ ² or an ellipse(x ₂?m)²/c²+(y₂?n)²/d²=1. The results show that the overall reliabilities of the solid solubilities for the 897 binary alloys based on the rare earth metals are 89.2% and 92.8% for the parabola and ellipse regularities respectively. The constants a and b in the parabola equation, andm, n, c andd in the ellipse equation are discussed, which can be related to some appropriate parameters for each host metal respectively.