Effect of hydrogen on the magnetic properties of Dy0.73Tb0.27Fe2−xCox [x = 0.5, 1.0, 2.0]
02 Jun 1996-Physica B-condensed Matter (North-Holland)-Vol. 223, pp 399-401
TL;DR: In this paper, the magnetic moments of the hydrides are found to be less than those of the unhydrided materials and the magnetization measurements carried out at 300 K showed large anisotropy and remanence for hydride of both x = 0.5 and 1.0 and these were further enhanced at 24 K.
Abstract: Dy0.73Tb0.27Fe2−xCox (x = 0.5, 1.0, 2.0) and their hydrides (hydrogen concentration n = 1.0) are found to crystallize in C15 cubic Laves phase. While the x = 0.5 and 1.0 materials and their hydrides have Curie temperatures above 300 K, the x = 2.0 material and its hydride are paramagnetic at 300 K. The magnetization measurements carried out at 300 K showed large anisotropy and remanence for hydrides of both x = 0.5 and 1.0 and these are found to be further enhanced at 24 K. These results are discussed on the basis of rhombohedral distortions of the crystal lattice. The magnetic moments of the hydrides are found to be less than those of the unhydrided materials.
TL;DR: In this article, the results of low temperature magnetization measurements carried out on the Dy 0.73 Tb 0.27 Fe 2− x Co x system and their hydrogenated compounds are presented.
Abstract: The results of low temperature magnetization measurements carried out on the Dy 0.73 Tb 0.27 Fe 2− x Co x system and their hydrogenated compounds are presented. Low temperature (12 K) magnetization data reveals a large increase in anisotropy in the hydrogenated compounds, attributed to a modification in crystalline electric field effects as a result of the orientational ordering of hydrogen atoms in the lattice. The discrete step-wise increase in magnetization upto a field of 2 kOe in the parent alloys and the hydrogenated compounds is attributed to spin–flip metamagnetism.
TL;DR: In this paper, the magnetic contribution to electrical resistivity is applied to estimate Curie temperatures, and the Curie temperature increases with x, approaches a maximum for x ǫ = 0.3 and reduces across the rest of the series.
Abstract: Electrical resistivity studies performed in a wide temperature range across the complete Fe/Co substituted Tb 0.27 Dy 0.73 (Fe 1− x Co x ) 2 intermetallic series, with a borderline compound Tb 0.27 Dy 0.73 Fe 2 known as Terfenol-D are presented. Parameters characterizing the dependence of resistivity on temperature, including the Debye temperature, are determined. Residual, phonon and magnetic contributions are separated from electrical resistivity. The magnetic contribution to electrical resistivity is applied to estimate Curie temperatures. Regions of weak and strong ferromagnetism of the transition metal sublattice are evidenced. The Curie temperature increases with x , approaches a maximum for x = 0.3 and reduces across the rest of the series. Some results of electronic band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method are also presented. A distribution function for the densities of 3 d states is introduced and a formula to estimate the band splitting energy is proposed. The obtained 3 d and 4 s band splitting energies for iron, cobalt and average for transition metal are presented. The Curie temperature across the Tb 0.27 Dy 0.73 (Fe 1− x Co x ) 2 system is described using a formula relating to both the FLAPW calculated magnetic moments and the statistical properties of the substituted transition metal sublattice.
10 Mar 2023
TL;DR: In this paper , the evolution of microstructure and texture upon directional solidification in rare earth transition metal based RFe2 type alloys has been addressed and the effect of alloying addition on the microstructures and magnetostrictive properties has been also presented.
Abstract: Magnetostriction is a unique property of magnetic materials where in the dimensions of the material changes due to the application of an external magnetic field. Of the several magnetic materials studied until now, rare earth (R) transition metal based RFe2 type alloys exhibit giant magnetostriction at room temperature. As a potential candidate for transducer and actuator applications, research and development of RFe2 alloys were mainly focused on anisotropy compensation, optimization of composition and grain orientation in order to achieve large magnetostriction at low magnetic fields. Large magnetostrictive strains at low magnetic fields have been found to be strongly influenced by the phases present in the microstructure and crystallographic texture. Adopting directional solidification techniques and selective alloying additions at rare earth and transition metal sites has been found to be beneficial in inducing the necessary texture and precluding the formation of deleterious phases in the microstructure. In this context, this chapter attempts to address the evolution of microstructure and texture upon directional solidification in RFe2 alloys. In addition to this, effect of alloying addition on the microstructure and magnetostrictive properties of RFe2 are also presented.
TL;DR: In this paper, the authors review available experimental information on the existence, thermodynamic stability and physical properties of hydrides formed by the absorption of hydrogen gas in intermetallic compounds of two transition metals.
Abstract: The authors review available experimental information on the existence, thermodynamic stability and physical properties of hydrides formed by the absorption of hydrogen gas in intermetallic compounds of two transition metals. The emphasis is on stability. It is shown that empirical models for the stability of ternary hydrides can be reconciled with ideas based on the results of band structure calculations of (binary) metallic hydrides. It is concluded that metallic hydrides can be looked upon as alloys of metallic hydrogen. In addition to the thermodynamic properties of ternary metallic hydrides the authors discuss experimental information on electronic properties (magnetic, super-conductivity, band structure features) and on crystallographic and metallurgical properties (neutron scattering, nuclear and electron spin resonance, Mossbauer spectroscopy, diffusion). Applications are briefly reviewed.
TL;DR: The change in the magnetic properties of the compounds YFe 2 and GdFe 2 upon hydrogen absorption has been studied by means of magnetic measurements and by Mossbauer effect measurements as mentioned in this paper.
Abstract: The change in the magnetic properties of the compounds YFe 2 and GdFe 2 upon hydrogen absorption has been studied by means of magnetic measurements and by Mossbauer effect measurements. In both compounds H 2 absorption leads to a drastic reduction in Curie temperature and to an increase in saturation magnetization. The Mossbauer spectra of the hydrides show appreciable line broadening. The hydride of YFe 2 gives rise to an increase in hyperfine splitting in the magnetically ordered region. The isomer shift in YFe 2 as well as in GdFe 2 changes on hydride formation. X-ray diffraction showed that the cubic Laves phase structure is retained, but that the lattice constants increase considerably when hydrogen is absorbed in GdFe 2 and YFe 2 .
Abstract: Rare‐earth transition metal compounds are known to be able to (reversibly) absorb large quantities of hydrogen gas at moderate pressures. This absorption of H2 gas leads to substantial changes of the magnetic properties. These include hydrogen induced transitions from Pauli paramagnetism to ferromagnetism. Examples also exist of the reverse effect, i.e., where in ferromagnetic compounds the 3d moment disappears upon hydrogen absorption. The changes in magnetic properties, together with experimental results of X‐ray diffraction and Mossbauer‐effect spectroscopy are discussed in terms of charge transfer and changes in interatomic distances. The metastable character of the ternary hydrides often leads to a loss of the long range atomic order upon hydrogen absorption. This affects not only the absorption capacity (after repeated cycling) but also influences the magnetic behavior. Examples are shown where the atomic disorder has led to pronounced thermomagnetic history effects.
TL;DR: In this paper, the influence of Ho substitution on the Co moments in (HoxY1-x)Co2 has been investigated by means of magnetic, resistivity and lattice parameter measurements.
Abstract: The influence of the Ho substitution on the Co moments in (HoxY1-x)Co2 has been investigated by means of magnetic, resistivity and lattice parameter measurements. A first-order phase transition and a field-induced metamagnetism can be detected for x>or=0.7. At the magnetic transition temperature anomalies of the lattice parameters were measured for x>or=0.3. In connection with the first-order transition a discontinuity in the rho (T) curves appears for x>or=0.7. For 0.3 150K) the rho (T) curves show a tendency to saturation, which is the same for all x values. Considering the substitution of Ho into YCo2 the existence of a critical RE concentration (x>0.1) for the appearance of a long-range magnetic order is evidenced. The Co moments mu Co are compared with neutron diffraction results. The overall agreement is very good and supports the assumption of induced Co moments. For the whole pseudobinary system, a Fermi energy situated in a steep flank of the density of states function was assumed.