Anisotropic Magnetostriction Research Articles

Magnetic and mechanical properties of rolled-up Au/Co/Au nanomembranes with multiple windings

Rolled-up Au/Co/Au microtubes with up to three windings were fabricated by the combination of strain engineering, conventional photolithography, and electron beam deposition. First, magnetization properties of the initial 2D film arrays and the corresponding tube arrays were studied and strong influences of magnetostrictive and shape anisotropy are observed. Second, the mechanical deformation was examined by an instrumented indentation technique at the nanoscale and analyzed by contact mechanics theory. The loading curve fitting in the elastic regime by the Hertz model provides a first approximation of the nanomembrane radial elastic modulus of about 135 GPa.

Thermal expansion anomaly and spontaneous magnetostriction of Gd 2Fe 17 compound

Materials with negative thermal expansion have many practical applications. However, these materials are known in only several oxide systems, and when the negative thermal expansion occurs, the contraction is usually small and limited to a narrow temperature range beyond room temperature. For obtaining a compound with negative thermal expansion in broad temperature range, the structural and magnetic properties of Gd 2Fe 17 compound were investigated by means of X-ray diffraction and magnetization measurements. The Gd 2Fe 17 compound annealed at 1050 °C had a Th 2Zn 17-type structure. There existed an anisotropic strong spontaneous magnetostriction and a negative thermal expansion in Gd 2Fe 17 compound. The average thermal expansion coefficients was ▪=−7.40×10 −6/K in the temperature range of 294–453 K and ▪=−1.80×10 −5/K in 453–534 K, respectively. The spontaneous magnetostrictive deformation ω S decreased from 4.34×10 −3 to near zero with temperature increasing from 294 to 572 K. The spontaneous linear deformation λ c was much larger than λ a at the same temperature below about 500 K.

Magnetostrictions and Magnetic Properties of Nd-Fe-B and SrFe12O19

The magnetostrictions of polycrystalline Nd-Fe-B and Sr-ferrite at different temperatures are reinvestigated using a strain gauge rotating-sample method. It is found that the magnetostriction λs of Nd-Fe-B is +52×10−6, and that of Sr-ferrite is −25 × 10−6 under a magnetic field of 8 T at room temperature. The maximum energy product (BH)max of the Nd-Fe-B magnet is improved when the powders are magnetically aligned perpendicular to the pressing direction, whereas that of the Sr-ferrite magnet is better when the powders are aligned parallel to the pressing direction. These experimental results suggest that the magnetostriction can generate compressive strain anisotropy resulting from the inverse effect of the magnetostriction. Thus, the magnetization of materials with a negative coefficient of magnetostriction are easier to be aligned normal to the stress direction, while for the materials with a positive coefficient of magnetostriction, the magnetization is easier to be aligned along the stress direction. Therefore, the magnetostriction anisotropy can be used to improve the alignment of the magnetic powders as well as the performance of the magnets.

Magnetoelastic effects in single-, poly-, and nanocrystalline iron- and cobalt-based rare-earth alloys and their hydrides

The magnetoelastic effects in intermetallic compounds with high contents of rare-earth and 3d transition metals are studied on (RR′R″)(Fe, Co)2, R2Fe14B, R2Fe17, and RFe11Ti compounds (R, R′, R″ = rare-earth metal (REM)) and their hydrides. The main laws of the formation of high magnetostrictive characteristics in the (RR′R″)(Fe, Co)2 compounds in different structural states are found. It is shown that hydrogenation of the compounds results in a substantial decrease in these characteristics. Hydrogenation and nitriding of the RFe11Ti and R2Fe17 compounds (R = magnetoactive ion) are found to change the sign of magnetostriction. The sign of magnetostriction and Stevens factor αJ for R ions are found to correlate with each other, which indicates a prevalent contribution of the REM sublattice to the anisotropic magnetostriction of these compounds. New materials exhibiting invar properties are formed as a result of the incorporation of hydrogen atoms into the crystal lattice of the R2Fe14B compounds. Magnetostrictive deformations are found to be highly sensitive to the structural state of all compounds under study.

Detailed study of ultra-soft magnetic properties of Fe74Cu0.8Nb2.7Si15.5B7

The magnetic properties of nanocrystalline Fe74Cu0.8Nb2.7Si15.5B7 alloy, which were rapidly solidified and then annealed at various temperatures between 475 and 650°C for different holding time, have been studied. Grain size, silicon content and the lattice parameter of α-Fe(Si) nanograins at the annealing temperatures were determined. Curie temperature of the amorphous phase was determined from the temperature dependence of permeability. For higher annealing temperatures and times, some Si diffused out of the α-Fe(Si) phase and formed an ordered DO3 phase of Fe3Si. This changed the overall magnetostriction and average anisotropy of the matrix, which deteriorated the magnetic softness of the material at higher annealing temperatures. Ultra-soft magnetic properties were achieved by averaging the random anisotropy via exchange interaction. Hysteresis loops for samples in as-cast and annealed conditions have also been studied.

Magnetoelastic properties of Nd 6Fe 13Cu intermetallic compound

Magnetoelastic properties of Nd 6Fe 13Cu intermetallic compound are reported. To study the magnetoelastic behaviour of this compound, the thermal expansion as well as the longitudinal ( λ l) and transverse ( λ t) magnetostriction were measured by using the strain gauge method in the selected temperature range of 80–500 K under applied magnetic fields up to 1.5 T. An anomaly and invar-type effects are observed in the linear thermal expansion and α( T) curves at the Néel temperature. The linear spontaneous magnetostriction decreases sharply by approaching the Néel temperature and also shows the short-range magnetic ordering effects when antiferromagnetic–paramagnetic transition occurs. In the low field region, the absolute values of the anisotropic magnetostriction are small and then start to increase with applied magnetic field. Each isofield curve of the anisotropic magnetostriction passes through a minimum and then approaches to zero with increasing temperature. This magnetostriction compensation arises from the difference in the magnetoelastic coupling constants of the sublattices in this compound.

Magnetoelastic properties of GdMn 6Sn 6 intermetallic compound

We studied the thermal expansion and magnetostriction of polycrystalline samples of GdMn 6Sn 6 intermetallic compound with hexagonal HfGe 6Fe 6-type structure in the temperature range of 77–520 K. The thermal expansion measurement of the sample shows anomalous behavior around its T C=434 K and T M=309 K, possibly the point of collapse-like reduction of Mn moments. In addition, the isofield curves of anisotropic and volume magnetostriction reveal anomalies around paramagnetic to ferrimagnetic phase transition. The obtained experimental results are discussed in the framework of two-magnetic sublattices by bearing in mind the lattice parameter dependence of interlayer Mn–Mn exchange interaction in this layered compound. From the temperature dependence of magnetostriction values and considering the magnetostriction relation of a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants as well as a comparison of their orders of magnitude for this compound.

A survey on the effect of vanadium content on the magnetoelastic properties of YFe12−xVx alloys

Experimental results on the thermal expansion and magnetostriction of YFe12−xVx (1.5≤x≤3.5) alloys are reported. The results show that the anisotropic magnetostriction (Δλ) at a finite field (1.5T) increases with increasing vanadium content in the range of x<2. But for x>2, a decrease in the magnetic anisotropy with increasing vanadium content causes a decrease in the saturation values of Δλ. In addition, the thermal expansion coefficient becomes a minimum for x≈2. Experimental curves exhibit that the forced volume magnetostriction (ΔV/V) is positive and increases linearly with the applied field at high fields. But in the low field region (≤0.5T), a minimum appears in the isothermal curves of ΔV/V around the saturation field. The results are explained by considering the influence of vanadium content on the magnetization anisotropy of YFe12−xVx compounds.

Resistive switching via the converse magnetoelectric effect in ferromagnetic multilayers onferroelectric substrates

A voltage-controlled resistive switching is predicted for ferromagnetic multilayers and spinvalves mechanically coupled to a ferroelectric substrate. The switching between low- andhigh-resistance states results from the strain-driven magnetization reorientations by about90°, which are shown to occur in ferromagnetic layers with a high magnetostriction and weakcubic magnetocrystalline anisotropy. Such reorientations, not requiring external magneticfields, can be realized experimentally by applying moderate electric field to athick substrate (bulk or membrane type) made of a relaxor ferroelectric havingultrahigh piezoelectric coefficients. The proposed multiferroic hybrids exhibiting giantmagnetoresistance may be employed as electric-write nonvolatile magnetic memory cellswith nondestructive readout.

Magnetic properties and structure of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi2Mn x (0 ≤ x ≤ 1.5)

Crystal structure, magnetization, coercive force, magnetic susceptibility, and anisotropic magnetostriction of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi2Mn x (0 ≤ x ≤ 1.5) have been studied. The samples with x ≤ 1 have an fcc structure, whereas TbNi2Mn1.25 has a rhombohedral structure of the PuNi3 type. It has been found that the magnetic ordering temperature increases sharply when manganese is added. As the Mn concentration grows, the magnetization and the magnetostriction decrease monotonically, while the coercive force increases. The experimental data obtained have been interpreted on the assumption that a partial substitution of manganese for terbium in TbNi2Mn x leads to local distortions of the crystal field acting on Tb ions, to the appearance of a local uniaxial random anisotropy, and to the formation of a noncollinear magnetic structure in the terbium sublattice.

Anisotropic magnetostriction in a ⟨110⟩ oriented crystal Tb0.36Dy0.64(Fe0.85Co0.15)2 after coaxial field annealing

Axial magnetostriction of Terfenol-D oriented crystals is highly anisotropic when changing the magnetization direction. Magnetostrictions of a ⟨110⟩ oriented crystal Tb0.36Dy0.64(Fe0.85Co0.15)2 were investigated under magnetic fields with a series of angles θ to its axis. Totally different anisotropic magnetostrictive behaviors are observed after annealing under a coaxial field of 240 kA/m. The magnetostriction for the field annealed specimen seems unsaturated even under 640 kA/m for angles θ in the range from 0° to 55°. At these angles, magnetostriction “ascending” is observed during the final magnetization process, while magnetostriction “dropping” occurs at angles above 35° for the untreated crystal. With the increase in angle θ, the corresponding field where magnetostriction starts dropping decreases for the untreated crystal, while the field at which magnetostriction starts ascending increases for the field annealed one. A simplified model based on moment “jump” and “rotation” is proposed to explain such anisotropic behaviors.

Magnetoelastics of a Spin Liquid: X-Ray Diffraction Studies ofTb2Ti2O7in Pulsed Magnetic Fields

We report high resolution single crystal x-ray diffraction measurements of the frustrated pyrochlore magnet Tb2Ti2O7, collected using a novel low temperature pulsed magnet system. This instrument allows characterization of structural degrees of freedom to temperatures as low as 4.4 K, and in applied magnetic fields as large as 30 Tesla. We show that Tb2Ti2O7 manifests intriguing structural effects under the application of magnetic fields, including strongly anisotropic giant magnetostriction, a restoration of perfect pyrochlore symmetry in low magnetic fields, and ultimately a structural phase transition in high magnetic fields. It is suggested that the magnetoelastic coupling thus revealed plays a significant role in the spin liquid physics of Tb2Ti2O7 at low temperatures.

Anomalous thermal expansion and magnetic properties of Tm2Fe17−xCrx compounds

The structural and magnetic properties of Tm2Fe17−xCrx (x=0, 0.5, 1.0, 1.5, and 2.0) compounds are investigated by means of x-ray diffraction and magnetization measurements. The Tm2Fe17−xCrx compounds have a hexagonal Th2Zi17-type structure. There exist a negative thermal expansion coefficient for Tm2Fe17−xCrx compounds near their Curie temperature and an anisotropic and strong spontaneous magnetostriction in the magnetic states of Tm2Fe17−xCrx compounds. In Tm2Fe17−xCrx compounds, Cr atoms substituting for Fe atoms can increase obviously the Curie temperature and the easy-axis magnetocrystalline anisotropy. The Curie temperature of Tm2Fe16Cr compound is about 160 K higher than that of the mother compound Tm2Fe17. The saturation magnetization of Tm2Fe17−xCrx compounds decreases with increasing Cr content.

Magnetotransport and magnetoelastic effects in Co-doped La0.7Sr0.3MnO3 nanocrystalline perovskites

La 0.7 Sr 0.3 Mn 1− x Co x O 3 ( x =0, 0.05, 0.1) nanoparticles, prepared by sol–gel method, were studied by means of X-ray diffraction, transmission electron microscopy , resistivity , magnetoresistance , thermal expansion and magnetostriction measurements. Results show that partial substitution of Mn by Co leads to a reduction in lattice parameters , enhancement of resistivity and room temperature magnetoresistance MR, decrease of metal-insulator transition temperature T MI and T C , an increase in thermal expansion coefficient, volume magnetostriction and anisotropic magnetostriction. The latter increases about one order of magnitude with 10% Co substitution. In comparison with Mn ions, the Co ions possess higher anisotropy energy, larger magnetostriction effect, smaller ionic size and spin state transitions with increase in temperature and magnetic field; this suggests that Co substitution leads to double-exchange interaction weakening, resulting in suppression of ferromagnetic long-range order and metallic state and increase of magnetic anisotropy . Furthermore, our samples have a relatively lower T MI and T C , higher resistivity and MR, compared with the reported values for similar compounds with larger particle sizes. This is attributed to the nanometric grain size and spin-polarized tunneling between neighboring grains.

Anomalous thermal expansion and spontaneous magnetostriction of Gd2Fe16Cr compound

The structural and the magnetic properties of Gd2Fe16Cr compound are investigated by x-ray diffraction and magnetization measurements. The Gd2Fe16Cr compound has a rhombohedral Th2Zn17-type structure. There exist an anisotropic strong spontaneous magnetostriction and a negative thermal expansion in the magnetic state of Gd2Fe16Cr compound. The average thermal expansion coefficient ᾱ = −7.03 × 10−6/K in a temperature range of 294–454 K and ᾱ = −1.31 × 10−5/K in 454–572 K are obtained. The spontaneous magnetostrictive deformation and the Curie temperature are discussed.

Magnetostriction and effective magnetic anisotropy of Co-contained Finemet nanocrystalline alloys

The microstructure and magnetic properties of Co-contained Finemet nanocrystalline alloys were investigated. By contrasting with Finemet, the Co-contained Finemet nanocrystalline alloys have a broad temperature range for precipitating a single α-FeCo crystalline phrase and a relatively higher Curie temperature of amorphous phase. After full nanocrystallization they exhibit improved high-temperature soft magnetic properties. However the room-temperature permeability of Co-contained Finemet was obviously lower than that of Finemet. For clarifying the reason, the effective magnetic anisotropy ⟨K⟩ and the saturation magnetostriction λs were measured, respectively, and the ⟨K⟩ of Co-contained Finemet is about 100–137 J/m3, which is the same order of magnitude as Finemet, but the λs of Co-contained Finemet-type alloy is much higher than that of Finemet which results in a relatively lower permeability.

In Situ Observation of Reversible Nanomagnetic Switching Induced by Electric Fields

We report direct observation of controlled and reversible switching of magnetic domains using static (dc) electric fields applied in situ during Lorentz microscopy. The switching is realized through electromechanical coupling in thin film Fe(0.7)Ga(0.3)/BaTiO(3) bilayer structures mechanically released from the growth substrate. The domain wall motion is observed dynamically, allowing the direct association of local magnetic ordering throughout a range of applied electric fields. During application of approximately 7-11 MV/m electric fields to the piezoelectric BaTiO(3) film, local magnetic domains rearrange in the ferromagnetic Fe(0.7)Ga(0.3) layer due to the transfer of strain from the BaTiO(3) film. A simulation based on micromagnetic modeling shows a magnetostrictive anisotropy of 25 kPa induced in the Fe(0.7)Ga(0.3) due to the strain. This electric-field-dependent uniaxial anisotropy is proposed as a possible mechanism to control the coercive field during operation of an integrated magnetoelectric memory node.

Magnetostriction Anisotropy and Rotational Magnetostriction of a Nonoriented Electrical Steel

Magnetostriction in nonoriented (NO) electrical steel is a possible source of vibration and acoustic noise in electrical machines. The anisotropy of the magnetostriction of NO steel can be far greater than that of its specific power loss which is often quoted. Also magnetostriction under rotational magnetization can be much higher than under alternating magnetization. This paper shows the relevance of magnetostrictive anisotropy to the rotational magnetostriction of a NO steel. An investigation of the effect of anisotropy in magnetostriction was carried out, followed by rotational magnetostriction measurements. A model based on an analogy of mechanical elasticity was used to describe the effect of magnetostrictive anisotropy on the rotational magnetostriction. Results show that a high value in rotational magnetostriction is mainly driven by its high magnetostriction in the transverse direction. The phenomenon is shown to be a source of asymmetrical deformation in the back iron of electrical machine cores where rotational flux predominates.

Magnetostriction of a U2Fe13Si4 single crystal

Abstract The longitudinal and transverse magnetostriction was measured on a single crystal of U2Fe13Si4 by a capacitor microdilatometer. Anisotropic magnetostriction constants λ 1 α , 2 , λ 2 α , 2 and λγ,2 of U2Fe13Si4 are found to be in the range (70–210) × 10−6 at 4.2 K that is high enough to be attributed to the U sublattice. A volume effect observed at the FOMP transition may indicate a field-induced non-collinearity, which involves the exchange magnetostriction to the process in addition to the anisotropic one. The high exchange magnetostriction of U2Fe13Si4 manifests itself in large volume-magnetostriction susceptibility above the technical saturation.

Effect of Magnetostriction Anisotropy in Nonoriented Electrical Steels on Deformation of Induction Motor Stator Cores

Magnetostriction in nonoriented (NO) electrical steels is a harmful source of vibration and acoustic noise in electrical machines. It is far more anisotropic than specific power loss, which results in more complexity in prediction of the vibration and acoustic noise. An investigation of the anisotropy in magnetostriction and mechanical elastic properties of a NO steel is presented in this paper. Measurements of deformation in the stator teeth of an induction motor model core were conducted in order to study the effect of the magnetostriction anisotropy. Strain due to Maxwell forces in the air gap was calculated and compared with the measured deformation. Measurement results indicate that anisotropic magnetostriction has a great impact on unsymmetrical deformation of the stator teeth of induction motor cores.