Volume Magnetostriction Research Articles

Multifunctional Phenomena in Rare-Earth Intermetallic Compounds With a Laves Phase Structure: Giant Magnetostriction and Magnetocaloric Effect

We report on the magnetic and thermal properties [magnetization, specific heat, thermal expansion, magnetostriction, and magnetocaloric effect (MCE)] for the three multicomponent systems Tb x Dy y Gd z Co 2 , Tb x Dy y Ho z (Co, Fe) 2 , and Tb x Dy y Er z (Co, Fe) 2 (x + y + z = 1). We show that for Tb x Dy y R z Co 2 , the Curie temperatures, TC (which ranged from 130 to 300 K), and order of the phase transition (first or second order) could be controlled by composition. The highest MCE values (the adiabatic temperature change ΔT ad = 2.2-2.3 K at μ 0 ΔH = 1.8 T) were observed for the compounds exhibiting the transitions of the first order. Giant volume magnetostriction of 1500-2000 and 500-600 ppm is demonstrated at a field of μ 0 H = 10 and 1.2 T, respectively. Structural and magnetic entropy contributions to the total isothermal entropy change are estimated for Tb x Dy y R z Co 2 . Regular recurrence and/or change of the physical properties across the varied composition of the compounds allows us to find the materials with desired magnetic characteristics, such as T C , MCE, and magnetostriction, to use them in practice.

Influence of melt temperature on the Invar effect in (Fe71.2B24Y4.8)96Nb4 bulk metallic glass

The influence of melt temperature on the glass formation, physical properties and local structure of (Fe71.2B24Y4.8)96Nb4 bulk metallic glass (BMG) was investigated through X-ray diffractometry, differential scanning calorimetry, thermal dilatation, and Mossbauer spectra tests. Amorphous alloys were formed by fast cooling of the melt from the temperature range of 1573–1773 K. BMG cast from 1623 K has lower Curie temperature and larger spontaneous volume magnetostriction, i.e., stronger Invar effect. The abnormality, which can not be eliminated by annealing, is attributed to the higher amount of Fe–Fe pairs indicated by the hyperfine field distribution. This special local structure is inherited from the melt, which has a liquid–liquid change manifested by an exothermic step region at the temperature range of 1615–1650 K. Through a slow-cooling process, the melt in the liquid–liquid change is frozen to a crystalline structure contained Y2Fe17 phase with a high intensity signal. These findings help explain the correlation between the liquid–liquid change and the structure of cooling products.

Magnetoelastic effects in La0.7Sr0.3−xCaxMnO3 nanocrystalline perovskites

Abstract La0.7Sr0.3−xCaxMnO3 (x=0, 0.1, 0.2 and 0.3) nanoparticles, prepared by sol–gel method, were studied by means of X-ray diffraction, transmission electron microscopy, thermal expansion and magnetostriction measurements. It was revealed that samples of low Ca concentration (x≤0.1) crystallize in rhombohedral perovskite structure with R-3c space group, and by increasing x, smaller Ca radius causes the lattice to convert to orthorhombic structure (space group of Pbnm). The results exhibit an anomalous behavior in the thermal expansion behavior of all samples, as well as temperature dependence of their volume magnetostriction being related to the presence of a conductive magnetic two-phase state at temperatures higher than TC. Moreover, the magnitude of this magnetovolume effect increases with x due to smaller Ca size, which softens the crystal lattice. The results show that Ca substitution results in weakening the double-exchange interaction and consequently reducing TC, as well as decreasing the magnetic anisotropy. Furthermore, our nanocrystalline samples have a relatively lower TC, compared with the reported values for similar compounds with larger particle size. Among them, the sample with x=0.2 possess TC value of about room temperature; to say by partial substitution of Ca for Sr we succeeded in adjusting the transition temperature of this series of manganites which was a main motivation for this research.

Magnetostriction and thermal expansion of HoFe11−xCoxTi intermetallic compounds

The thermal expansion and magnetostriction of the HoFe11−xCoxTi (0≤x≤11) alloys have been investigated, using the strain gauge technique in the temperature range 77–600K. Both thermal expansion and thermal expansion coefficient exhibit an anomalous behaviour and Invar effect below Curie temperature (TC=516K) in sample with x=0. The increase of x in HoFe11−xCoxTi system leads to disappearing of the Invar effect and increasing of the average thermal expansion coefficient from 6.370×10−6K−1 in x=0 to 10.735×10−6K−1 in x=11 below room temperature. In addition, the spontaneous volumemagnetostriction decreases with Co content. The magnetostriction compensation point is observed in the anisotropic magnetostriction curve of all samples. The maximum value of anisotropic magnetostriction (Δλ≈50×10−6) at room temperature is observed in sample with x=9. The saturation behaviour only appears in samples with x=5, 7 and 9. In samples with x=3, 5 and 7, a noticeable volume magnetostriction (ΔV/V) is observed in low temperature due to first-order magnetisation process. Moreover, ΔV/V exhibits a large anomaly about 45×10−6 and 20×10−6 around room temperature related to spin reorientation transition in samples with x=9 and 11, respectively. The results are discussed based on the local magnetic moment model and irreducible magnetoelastic coupling modes.

Magnetovolume effects in manganese nitrides with antiperovskite structure

Magnetostructural correlations in antiperovskite manganese nitrides were investigated systematically for stoichiometric and solid solution Mn3Cu1−xAxN (A = Co, Ni, Zn, Ga, Ge, Rh, Pd, Ag, In, Sn or Sb). This class of nitrides is attracting great attention because of their giant negative thermal expansion, which is achieved by doping Ge or Sn into the A site as a relaxant of the sharp volume contraction on heating (spontaneous volume magnetostriction ωs) because of the magnetovolume effects. The physical background of large ωs and mechanism of how the volume contraction becomes gradual with temperature are central concerns for the physics and applications of these nitrides. An entire dataset of thermal expansion, crystal structure and magnetization demonstrates that the cubic triangular antiferromagnetic state is crucial for large ωs. The intimate relationship between ωs and the magnetic structure is discussed in terms of geometrical frustration related to the Mn6N octahedron and magnetic stress concept. The results presented herein also show that ωs depends on the number of d electrons in the A atom, suggesting the important role of the d orbitals of the A atom. Not all the dopants in the A site, but the elements that disturb the cubic triangular antiferromagnetic state, are effective in broadening the volume change. This fact suggests that instability neighboring the phase boundary is related to the broadening. The relation between the gradual volume change and the local structure anomaly is suggested by recent microprobe studies.

Exploring the magneto-volume anomalies in Dy2Fe17 with unconventional rhombohedral crystal structure

We have synthesized the Dy2Fe17 alloy with an unconventional crystal structure (R3¯m space group). Neutron powder thermo-diffraction and X-ray powder diffraction under high pressure (up to 15GPa) show that the rhombohedral crystal structure is stable. Likewise, the alloy with the usual hexagonal crystal structure (P63/mmc), the rhombohedral variant of Dy2Fe17 compound, exhibits a collinear ferrimagnetic order below the Curie temperature (TC≈363K), with antiparallel mutual alignment of the Dy and Fe sublattices. Additionally, we have observed two distinctive issues related to magneto-volume anomalies: (i) the pressure dependence of the cell volume at room temperature shows the existence of a critical pressure at which the compound is no longer ferrimagnetic; and (ii) the cell volume shows invar-like behaviour in a wide temperature range (2–290K), with a minimum at T≈380K. The spontaneous volume magnetostriction reaches ωS=1.6×10−2 at 2K that decreases to zero at T≈500K (≈1.4 TC), which is associated with the existence of short-range magnetic correlations.

Large magnetovolume effects due to transition from the ferromagnetic to antiferromagnetic state in Hf0.825Ta0.175Fe2 intermetallic compound

Intrinsic magnetic properties and magnetovolume effects have been investigated for the Hf0.825Ta0.175Fe2 itinerant-electron system, which exhibits a temperature-induced first-order transition from the ferromagnetic (FM) to the antiferromagnetic (AFM) state. The spontaneous volume magnetostriction contraction due to this transition from the high-volume FM state to the low-volume AFM state is about 0.66%. Applying a magnetic field increases significantly the FM–AFM transition temperature TFM–AFM, with a rate of 7.2 K T−1. At temperatures T > TFM–AFM a first-order metamagnetic transition between the AFM and FM states has been observed from isothermal magnetization curves, a result attributed to the itinerant-electron character of the Fe magnetism. This AFM–FM transition is accompanied by a huge field-induced volume magnetostriction. The change in ΔV/V due to the AFM–FM transition is about 0.75%.

Magnetostriction effect of Co substitution in the Nd6Fe13Si intermetallic compound

We studied the magnetostriction of Nd6Fe13−xCoxSi (x = 0, 1) intermetallic compounds with tetragonal Nd6Fe13Si-type structure, using the strain gauge method in the temperature range of 77–600 K under applied magnetic fields up to 1.5 T. The anisotropic magnetostriction (Δλ) versus temperature of the studied samples has shown almost similar field-dependence behavior. Below the spin reorientation temperature (TSR), Δλ changes its sign from positive to negative value at an applied threshold field which increases with decreasing temperature. This behavior may originate from the reduction of the magnetocrystalline anisotropy with temperature. It is also observed that absolute value of Δλ increases by Co substitution. On the other hand, the volume magnetostriction (ΔV/V) versus field shows different behavior. The ΔV/V curves of Nd6Fe12CoSi tend to have a nearly quadratic dependence on applied field near magnetic ordering temperature as expected for the parastrictive behavior. The temperature dependence of magnetostriction values is discussed based on the magnetostriction relation of the tetragonal structure to determine the signs of some of magnetostriction constants for these polycrystalline compounds.

The magnetoelastic properties of Co-rich Ho(Fe,Co,Ti)12 intermetallic compounds near the spin reorientation transition

The thermal expansion and magnetostriction of Co-rich HoFe11−xCoxTi compounds were investigated; using the strain gauge method in the temperature range 77–560K, under applied magnetic fields up to 1.5T. Both linear thermal expansion coefficient and volume magnetostriction of HoFe2Co9Ti exhibit a large anomaly near the spin reorientation transition. In HoCo11Ti sample, this anomaly is only present in the volume curve at the spin reorientation transition. The temperature dependence of anisotropic magnetostriction shows a similar behaviour in both samples. There is no saturation in the isotherm curves of anisotropic magnetostriction in HoCo11Ti compound. In contrast, saturation behaviour starts approximately from T=410K in HoFe2Co9Ti. The magnetovolume effect in Fe-containing compound at around spin reorientation transition in the maximum available magnetic field is approximately two times larger than that in the other sample. The anisotropic and volume magnetostriction results are discussed in terms of the contribution of magnetostriction attributed to the magnetic sublattices R and T and the local magnetic moment model.

Magnetovolume Effects in Strongly and Intermediately Correlated Electron Systems

Analyses of magnetovolume effects such as the forced volume magnetostriction and the thermal expansion anomaly can give estimation of local amplitude of spin fluctuations. We have shown that bcc Fe has a rigid magnetic moment and that the magnetic moment of Invar type alloys is rather soft. It is pointed out that the total energy difference between the magnetized state and the nonmagnetic state obtained by self-consistent energy band calculations using a local-spin-density approximation is much higher than the Curie temperature for rigid spin systems and comparable for soft spin systems. The effects of zero point spin fluctuations observed in the YMn2 system are discussed.

Magnetoelastic Anomalies Exhibited by Ni–Fe(Co)–Ga Polycrystalline Ferromagnetic Shape Memory Alloy

The martensitic transformation (MT) as well as the structure, magnetic and magnetostrain properties of a polycrystalline Ni50.1Fe18.6Ga27.2Co4.1 (at%) ferromagnetic shape memory alloy are investigated. The studied alloy exhibits a martensitic ferromagnetic phase near room temperature that shows a non-modulated tetragonal structure with a tetragonality ratio of c/a > 1. Strain measurements reveal a complex spontaneous change at MT amounting to about 0.15% that increases up to 0.22% at 5T of the applied magnetic field indicating orientation influence of the field on the martensitic variants growth. Magnetostrain measurements enable evaluation of the magnetic fieldinduced strain effect in the vicinity of MT. The sample shows moderate deformation achieving values of 70ppm related to the magnetization rotation and volume magnetostriction that does not saturate at applied magnetic field of 5T. [doi:10.2320/matertrans.M2013154]

De Haas-van Alphen effect, magnetization, magnetoresistance and magnetostriction of GdB4 as compared with TmB4

De Haas-van Alphen (dHvA) effect measurements were performed on GdB4 single crystal (R 300 K/R 4.2 K ≈ 12) in AFM state from 1.5 to 4.2 K in magnetic fields up to 14 T. 12 main branches of the oscillations were observed in the frequency range (0.1 ÷ 28) × 102 T. The angular dependence of the dHvA spectrum suggests a strongly anisotropic Fermi surface. Corresponding cyclotron masses m* c are light, ranging from 0.2 to 0.8m 0. We studied additionally the magnetization of GdB4, linear and volume magnetostriction, and magnetoresistance of GdB4 in comparison with the same properties of TmB4 single crystal above 1.5 K in the field of 0 ÷ 14 T. At 4.2 K and H || ⟨110⟩ collinear to the GdB4 easy magnetization axis the volume magnetostriction revealed the lattice contraction with the field rise excluding the range of H ≈ (11 ÷ 13) T, where the lattice expansion is accompanied by a sharp magnetization increase due to the destruction of its non-collinear magnetic structure. The magnetostricive behavior in GdB4 and TmB4 is different due to the CEF effect.

Charge and magnetization transport in Cd0.81Mn0.19GeP2 dilute magnetic semiconductor under high pressures

Cd0.81Mn0.19GeP2 dilute magnetic semiconductor (DMS) has been subjected to a complex study of electric and magnetic properties under high hydrostatic pressures of up to 7 GPa with pressure rise and release. Electrical resistivity, Hall factor, transverse magnetoresistance, relative magnetic susceptibility, and volume magnetostriction have been measured. Compressibility (k) and spontaneous magnetization coefficient (ωS) have been calculated.

Magnetostriction of the polycrystalline Fe80Al20 alloy doped with boron

The doping of Fe80Al20 polycrystalline alloy with 2% of boron increased the total magnetostriction twofold compared to a sample without boron. A value close to 80ppm was achieved at 300K. The microstructures of the boron-doped alloys show a dendritically solidified matrix with interdendritic α-FeAl and/or Fe3Al and Fe2B eutectic between the grains. The XRD analysis reveals an increase in the volume fraction of α-FeAl and a correspondent decrease of the Fe3Al phase volume fraction as the boron content increases. The increase of the volume fraction of this tetragonal Fe2B phase in the samples doped with boron causes the decrease of the strong volume magnetostriction that was observed in the alloy without boron. There is some evidence that the improvement of the magnetostriction magnitude due to the addition of boron to the Fe80Al20 alloy could reach the maximal magnetostriction if the 1:1 optimal ratio of the volume fractions of the α-FeAl and Fe3Al phases could be reached.

Influence of low Co substitution on magnetoelastic properties of HoFe11Ti intermetallic compound

The thermal expansion and magnetostriction of HoFe11−xCoxTi (x=0, 0.3, 0.7 and 1) intermetallic compounds were measured, using the strain gauge method in the temperature range 77–590K under applied magnetic fields up to 1.5T. Results show that for samples with x=0 and 0.3, both linear thermal expansion and linear thermal expansion coefficient exhibit anomalies below the Curie temperature. Below room temperature, the spontaneous volume magnetostriction decreases with Co content. For all compounds studied, the anisotropic magnetostriction shows similar behaviour in the measured temperature range. The magnetostriction compensation occurs above room temperature in all samples. The volume magnetostriction shows a linear dependence on the applied field and by approaching the Curie temperature this trend changes to parastrictive behaviour. The results of the spontaneous magnetostriction are discussed based on the local magnetic moment model. The contribution of magnetostriction attributed to the magnetic sublattices R and T (Fe or Co) is discussed.

Thermal expansion anomaly and magnetostriction of Nd2Fe14Si3 intermetallic compound

The thermal expansion and magnetostriction of Nd2Fe14Si3 polycrystalline intermetallic compound was measured, using the strain gauge method in the temperature range 77–590K under applied magnetic fields up to 1.5T. Results show that both linear thermal expansion and linear thermal expansion coefficient exhibit anomalies below Curie temperature. A pronounced positive spontaneous volume magnetostriction has been observed below the Curie temperature. The spontaneous volume magnetostriction decreases with Si substitution in Nd2Fe17 compound. The saturation trend of the anisotropic magnetostriction below 115K depends on the saturation of the λγ mode. In the low field region (μ0H<0.3T), a minimum appears in the isothermal curves of the volume magnetostriction that may be attributed to the domain walls motion and rotation of the magnetic moments of domains toward the applied field direction. The results of the spontaneous and anisotropic magnetostriction are discussed based on the local magnetic moment model and irreducible magnetoelastic coupling modes, respectively.

Anomalies of magnetic properties and magnetovolume effect in Cd1−xMnxGeAs2 at hydrostatic pressure

We present the experimental results of the effect hydrostatic pressure up to P ≤ 7 GPa applied at the room temperatures in diluted magnetic semiconductor Cd1−xMnxGeAs2 (x = 0.06 − 0.3). We have found the pressure areas at which anomalies in magnetic properties were observed. Induced by hydrostatic pressure at P &amp;gt; 1.5 GPa magnetic phase transitions, interpreted as metamagnetic transition, were observed. The transitions from magnetic-ordered into magnetic disordered phases in region P &amp;gt; 4.1 GPa on the pressure dependences of relative volume compressibility were detected. We estimated the values of bulk modulus and volume magnetostriction. It is shown that high pressures significantly decrease the Curie temperature with values dTC/dP ≈ (−14.0 ÷ −6.8) K/GPa.

Temperature dependent magnetostrains in polycrystalline magnetic shape memory Heusler alloys

Abstract The transformation-induced strains with and without applied magnetic field and magnetostriction loops at different temperatures have been measured for polycrystalline ferromagnetic and metamagnetic shape memory Heusler alloys such as Ni Mn Ga, Ni Fe(Co) Ga and Ni Mn Sn, respectively. The results evidence a magnetic field oriented growth of martensitic variants during the martensitic transformation in Ni Mn Ga sample, whereas this effect is not evident in the other two alloys. In the Ni Mn Sn alloy, the isotropic volume magnetostriction dominates the anisotropic domain magnetostriction.

Magnetoelastic and elastocaloric effects in rare-earth metals, their alloys and compounds in the region of magnetic phase transitions

This article discusses experimental data and their theoretical interpretation concerning the volume magnetostriction, spontaneous magnetostriction, variation of magnetization under the action of pressure, and elastocaloric effects in rare-earth metals, as well as their alloys and compounds. Particular attention is paid to the region of phase transitions. The volume magnetostriction ω of true magnetization was investigated near the Curie temperature Θ as a function of magnetization and determined from the change of magnetostriction under the action of pressure. From these data we obtained the dependence of the exchange integrals on the unit cell volume. Giant volume magnetostriction and magnetoelastic elastocaloric effects were discovered in the rare-earth metals and alloys in the region of their magnetic phase transitions. It was established that giant volume magnetostriction in RCo2 compounds is caused by a critical increase of the magnetic moment of the 3d sublattice of cobalt in magnetic fields that exceeds the critical field at T > Θ. Giant volume magnetostriction in R2Fe17 compounds near the temperature Θ is shown to occur due to strong deformational dependences of exchange interaction and the value of the 3d electron bandwidth.

Magnetic, magnetocaloric, and lattice properties of the La(Fe x Si1 − x )13 ferromagnets

The magnetic and lattice properties of a sample of La(Fe0.86Si0.14)13 ferromagnet have been measured. The influence that neutron irradiation has on the physical properties of this ferromagnet is studied. It is shown that the irradiation of this sample by a fluence of 3 × 1019 n/cm2 increases the lattice constant a and the Curie temperature (TC) as the volume magnetostriction decreases. A model of ferromagnet is proposed which satisfactorily describes the dependence a(T) of the initial and irradiated samples and their magnetic properties. The temperature dependence of the change in entropy when switching the magnetic field on and off is calculated. It is established that the change in both the magnetic and lattice parts of the total entropy at the magnetic phase transition must be taken into account for La(FexSi1 − x)13 compounds.