MgCu2-type Structure Research Articles

Structure and magnetostriction of Tb0.4Nd0.6(Fe0.8Co0.2) x alloys

Structural, magnetic and magnetostrictive properties of Tb0.4Nd0.6(Fe0.8Co0.2)x (1.50 ≤ x ≤ 1.90) alloys have been investigated by means of X-ray diffraction (XRD), a vibrating sample magnetometer and a standard strain technique. XRD analysis shows the presence of single Laves phase with a cubic MgCu2-type structure for the high Nd content alloy around the composition of x = 1.80, which tends to be formed by curing at relatively low annealing temperature. The easy direction of magnetization at room temperature is observed toward axis, accompanied by a rhombohedral distortion with a large spontaneous magnetostriction λ111. An optimized effect on the linear anisotropic magnetostriction, 360 ppm at 3 kOe, was observed for the high Nd content Tb0.4Nd0.6(Fe0.8Co0.2)1.80 alloy, which can be attributed to its single Laves phase, the large λ111 (~1,520 ppm) of the MgCu2-type (Tb,Nd)(Fe,Co)2 phase and the good soft magnetic behaviors.

Low temperature crystal structure and magnetic properties of RAl2

Low temperature crystal structure and magnetic properties of RAl2 (R = Pr and Nd) have been studied using temperature dependent powder x-ray diffraction, magnetization, and heat capacity measurements. Unlike PrAl2, NdAl2 retains cubic MgCu2-type structure from room temperature down to 5 K, which is also confirmed from first principles electronic structure calculations. The magnetization measurements show both PrAl2 and NdAl2 order ferromagnetically at TC = 32 K and 77 K, respectively. However, the magnetization measurements show the former is a hard ferromagnet compared to the latter which is a soft ferromagnetic material. The magnetic entropy change obtained from heat capacity measurements at ΔH = 30 kOe for PrAl2 and NdAl2 are 3.15 J mol−1 K−1 and 1.18 J mol−1 K−1, respectively.

Magnetism and magnetocaloric effect in multicomponent Laves-phase compounds: Study and comparative analysis

This paper presents a review and results of comparative study of the influence of Gd on some physical properties of (R0.9R′0.1)1−xGdxCo2 solid solutions with R=Dy, Ho and R′=Er, Ho and x varied from 0.05 to 0.15. Powder X-ray diffraction analysis performed at room temperature revealed that all studied solid solutions solidify with the formation of a Laves-phase MgCu2-type structure (space group Fd−3m). The magnetization behavior and the magnetic transition are analyzed in terms of the Landau theory. The studies of magnetic properties and heat capacity showed that a relatively small Gd addition significantly increases TC of the compounds. The maximum percentage increase in TC, namely, ~43% was observed for (Ho0.9Er0.1)1−xGdxCo2. However, the highest temperature was noted for the (Dy0.9Ho0.1)0.85Gd0.15Co2 solid solution; it is TC=183.4K. Below the ordering temperature, all samples are ferrimagnetically ordered; at high temperatures, they are Curie–Weiss paramagnets. Moreover, a small Gd addition eliminates the field-induced magnetic transition near TC and, as consequence, transforms the nature of magnetic transition from the first- to second-order.The magnetocaloric effect has been estimated in terms of both isothermal magnetic entropy and adiabatic temperature changes. The highest adiabatic temperature change ΔTad=3K and highest isothermal entropy change ΔSmag=12.1J/kgK were observed for (Ho0.9Er0.1)0.95Gd0.05Co2 at ~90K in magnetic fields of 2T and 3T, respectively. A decrease in the entropy change has been observed with increasing Gd content in all studied samples. The smallest values of ΔSmag were observed for the (Dy0.9Ho0.1)1−xGdxCo2 solid solutions. Under an external field change of from 0 to 3T, the maximum entropy change for (Dy0.9Ho0.1)1−xGdxCo2 compounds decreases from 6.9at x=0.05–4.3J/kgK at x=0.15. The refrigerant capacity for all solid solutions (with 0.05≤x≤0.15) is reported. The effect of increasing Gd content in the solid solutions on their magnetic and magnetocaloric properties is discussed.

Texture-induced enhancement of the magnetocaloric response in melt-spun DyNi2 ribbons

The magnetocaloric properties of melt-spun ribbons of the Laves phase DyNi2 have been investigated. The as-quenched ribbons crystallize in a single-phase MgCu2-type crystal structure (C15; space group Fd3¯m) exhibiting a saturation magnetization and Curie temperature of MS = 157 ± 2 A m2 kg−1 and TC = 21.5 ± 1 K, respectively. For a magnetic field change of 2 T, ribbons show a maximum value of the isothermal magnetic entropy change |ΔSMpeak| = 13.5 J kg−1 K−1, and a refrigerant capacity RC = 209 J kg−1. Both values are superior to those found for bulk polycrystalline DyNi2 alloys (25% and 49%, respectively). In particular, the RC is comparable or larger than that reported for other potential magnetic refrigerants operating at low temperatures, making DyNi2 ribbons promising materials for use in low-temperature magnetic refrigeration applications.

The Microstructure and Magnetic Properties of TbDyHo (FeMn)<sub>1.95</sub> Alloys

The composition dependence of crystal structure, lattice parameter, micromorphology, Curie temperatures, magnetocrystalline anisotropy constant of Tb0.29Dy0.48Ho0.23(Fe1-XMnX)1.95(x0.3) alloys were investigated by the experiment. X-ray diffraction patterns demonstrate the Tb0.29Dy0.48Ho0.23(Fe1-XMnX)1.95(x0.3) alloys possess MgCu2-type cubic Laves structure. The lattice parameter of Tb0.29Dy0.48Ho0.23(Fe1-XMnx)1.95alloy increases with increasing of x value. The Curie temperature Tcdecreases from 375°C for x=0 to 316 °C for x=0.05, 265°C for x=0.1. The magnetocrystalline anisotropy constant K1of Tb0.29Dy0.48Ho0.23(Fe1-xMnx)1.95(x0.3) decreases slightly with the increasing of x value. The magnetostriction was examined under applied magnetic field H in the room temperature. The Tb0.29Dy0.48Ho0.23(Fe1-xMnx)1.95(x0.2) alloys have the character of giant magnetostrictive in room temperature. With the increasing of Mn concentration, the magnetostrictive of Tb0.29Dy0.48Ho0.23(Fe1-xMnx)1.95(x0.2) alloy decreased.

β-Mn-Type Co8+xZn12–x as a Defect Cubic Laves Phase: Site Preferences, Magnetism, and Electronic Structure

The results of crystallographic analysis, magnetic characterization, and theoretical assessment of β-Mn-type Co-Zn intermetallics prepared using high-temperature methods are presented. These β-Mn Co-Zn phases crystallize in the space group P4(1)32 [Pearson symbol cP20; a = 6.3555(7)-6.3220(7)], and their stoichiometry may be expressed as Co(8+x)Zn(12-x) [1.7(2) < x < 2.2(2)]. According to a combination of single-crystal X-ray diffraction, neutron powder diffraction, and scanning electron microscopy, atomic site occupancies establish clear preferences for Co atoms in the 8c sites and Zn atoms in the 12d sites, with all additional Co atoms replacing some Zn atoms, a result that can be rationalized by electronic structure calculations. Magnetic measurements and neutron powder diffraction of an equimolar Co:Zn sample confirm ferromagnetism in this phase with a Curie temperature of ∼420 K. Neutron powder diffraction and electronic structure calculations using the local spin density approximation indicate that the spontaneous magnetization of this phase arises exclusively from local moments at the Co atoms. Inspection of the atomic arrangements of Co(8+x)Zn(12-x) reveals that the β-Mn aristotype may be derived from an ordered defect, cubic Laves phase (MgCu2-type) structure. Structural optimization procedures using the Vienna ab initio simulation package (VASP) and starting from the undistorted, defect Laves phase structure achieved energy minimization at the observed β-Mn structure type, a result that offers greater insight into the β-Mn structure type and establishes a closer relationship with the corresponding α-Mn structure (cI58).

Magnetostrictive properties of Tbx(Pr0.5Nd0.5)1−xFe1.93 cubic Laves alloys

Polycrystalline Tbx(Pr0.5Nd0.5)1−xFe1.93(0.0⩽x⩽0.4) cubic Laves alloys were synthesized by arc-melting and subsequent high-pressure annealing. The structure, magnetic properties and magnetostriction of the alloys were investigated. These alloys exhibit single cubic Laves phase with MgCu2-type structure due to the effects of high-pressure annealing. The absolute value of the first anisotropy constant |K1| decreases with increasing Tb content to a minimum at x=0.1 and then increases with further increase in x. The magnetostriction λa=λ‖-λ⊥ of the sample with x=0.1 is much larger and easier to get saturation than the others. In addition, the large ratio between magnetostriction and the absolute values of the first anisotropy constant λa/|K1| appears at the sample with x=0.1, which may make it a potential material for magnetostrictive application.

Experimental study of the magnetocaloric effect in Dy1−xErxCo2 solid solutions doped with Gd

Magnetic and magnetocaloric properties of polycrystalline (Dy0.9Er0.1)1−xGdxCo2 (0.0 ⩽ x ⩽ 0.25) solid solutions were investigated experimentally using magnetic measurements. The magnetization behavior and magnetic transition are analyzed in terms of Landau theory. Powder X-ray diffraction analysis performed at room temperature showed that all (Dy0.9Er0.1)1−xGdxCo2 (0.0 ⩽ x ⩽ 0.25) solid solutions are C15 cubic Laves phase with the MgCu2-type structure. The lattice parameter increases from 0.7187 for Dy0.9Er0.1Co2 to 0.7204 nm for (Dy0.9Er0.1)0.75Gd0.25Co2. In this case, the Curie temperature increases from 128 K to 215 K for. At higher temperatures, all solid solutions are Curie–Weiss paramagnets. The isothermal entropy change −ΔSmag was calculated using magnetic measurements data and thermodynamic Maxwell’s relation. A decrease in the entropy change has been observed with increasing Gd content. Under an external field change of from 0 to 3 T, the maximum entropy change for these compounds decreases from 8.5 at x = 0.0 to 3.1 J/kg K at x = 0.25. The refrigerant capacity of the (Dy0.9Er0.1)1−xGdxCo2 solid solutions (with 0.0 ⩽ x ⩽ 0.25) is presented. The effect of increasing Gd content in the (Dy0.9Er0.1)1−xGdxCo2 solid solutions on their magnetic and magnetocaloric properties is discussed.

X-ray investigation of the Y–Zr–Ni system at 870 K

The isothermal section of the Y–Zr–Ni phase diagram at 870 K has been investigated by means of X-ray and microstructure analyses. One ternary compound YxZr1−xNi2 (0.12 ≤ x ≤ 0.20) occurs in the system. The crystal structure of Y0.12Zr0.88Ni2 has been investigated by single crystal X-ray diffraction: MgCu2 type structure, space group Fd-3m, a = 6.937(1) Å, Z = 8, R1 = 0.037 for 48 independent reflections Io > 2σ(Io)). Isotypic compounds with heavy rare earths RxZr1−xNi2 (x ∼ 0.12) (R = Gd–Lu) have been synthesized. The crystal structure of the binary compound ZrNi5 has been refined for the first time from the single crystal X-ray diffraction data: AuBe5 type structure, space group F-43m, a = 6.687(1) Å, Z = 4, R1 = 0.035 (wR2 = 0.036) for 63 reflections with Io > 2σ(Io). A morphotropic row of binary Laves phases Y0.97Ni2 (TmNi2-type structure, or as can be denoted “MgCu2”) towards ternary YxZr1−xNi2 (MgCu2 type structure) has been discovered.

Magnetic properties and magnetostriction of PrxNd1−xFe1.9 (0 ≤ x ≤ 1.0) alloys at low temperature

The crystal structure, magnetic and magnetostrictive properties of high-pressure synthesized PrxNd1−xFe1.9 (0 ≤ x ≤ 1.0) alloys were studied. The alloys exhibit single cubic Laves phase with MgCu2-type structure. The initial magnetization curve reveals that Pr0.2Nd0.8Fe1.9 has a minimum magnetocrystalline anisotropy at 5 K. The magnetostriction curve at 5 K shows that Pr0.2Nd0.8Fe1.9 has a very good low-field magnetostrictive property, and the magnetostriction of the PrxNd1−xFe1.9 alloy in high magnetic field is attributable mainly to Pr. The temperature dependence of the magnetostriction (λ‖) at the field of 5 kOe shows that the substitution of Nd reduces the K1 remarkably, and the values of λ‖ of Pr0.2Nd0.8Fe1.9 and Pr0.8Nd0.2Fe1.9 alloys are nearly five times larger than that of the PrFe1.9 alloy below 50 K; the λ‖ of Pr0.8Nd0.2Fe1.9 reaches up to 1082 ppm at 100 K, which makes it a potential candidate for application in this temperature range.

Structure and Magnetostriction of Pr&lt;sub&gt;x&lt;/sub&gt;Tb&lt;sub&gt;1-x&lt;/sub&gt;Fe&lt;sub&gt;1.9&lt;/sub&gt;Ti&lt;sub&gt;0.1&lt;/sub&gt; Alloys

The structure and magnetostriction have been investigated for PrxTb1-xFe1.9Ti0.1 alloys by means of the X-ray diffraction phase analysis, vibrating sample magnetometer, and standard strain gauge technique. Comparing the structure of bulk and annealed samples, it can be found that the annealing treatment is of benefit to the formation of single phase with MgCu2-type crystal structure when x0.3. The magnetization at the maximal magnetic field decreases rapidly with increasing Pr content. The magnetostriction for Pr0.2Tb0.8Fe1.9Ti0.1 annealed sample at 900kA/m is 1733ppm. The magnetostriction for PrxTb1-xFe1.9Ti0.1 alloys at 900kA/m also decreases with increasing Pr content.

Structure and magnetostriction of Tb0.4Nd0.6(Fe0.8Co0.2)1.90 alloy prepared by solid-state synthesis

Mechanical alloying (MA) and subsequent solid sintering process was used to prepare the Nd-containing magnetostrictive Tb0.4Nd0.6-(Fe0.8Co0.2)1.90 alloy. The structure, thermal stability and phase transformation were investigated as functions of composition, milling process and annealing temperature. An amorphous phase was formed by high-energy ball milling for 5 h with the ball-to-powder weight ratio of 20:1, which crystallized into MgCu2-type and PuNi3-type crystalline structure with different annealing temperatures. The magnetoelastic properties were investigated by means of a standard strain technique. The high Nd-content (Tb,Nd)(Fe,Co)2 Laves phase for the composition Tb0.4Nd0.6(Fe0.8Co0.2)1.90 was synthesized by MA process plus annealing at 500 °C for 30 min.

Effect of Mn substitution on the phase transition and magnetocaloric effect in Dy(Co1−xMnx)2 alloys

Series of Dy(Co1−xMnx)2 alloys (x=0, 0.02, 0.04, 0.06, 0.08, and 0.1) have been prepared by arc-melting method. All samples crystallize in single phase with C15 cubic MgCu2-type structure. The nature of phase transition was determined by the results of Arrott plots and Ac susceptibility, and no first order phase transition was observed for samples with x⩾0.02. With the increase of Mn content, Curie temperature increases linearly, while the calculated magnetic entropy change shows an obvious decrease with a broader peak, which could be explained by the change of phase transition type.

MgCuAl2-type Intermetallics REPdCd2(RE = Ce, Pr, Nd, Sm)

The cadmium-rich intermetallic compounds REPdCd2 (RE=Ce, Pr, Nd, Sm) were obtained by high-frequency melting of the elements in sealed niobium ampoules and subsequent annealing in muffle furnaces. The REPdCd2 phases crystallize with the orthorhombic MgCuAl2-type structure, space group Cmcm. The structure of NdPdCd2 was refined from single-crystal X-ray diffractometer data: a=421.9(3), b=995.4(7), c=834.5(6) pm, wR=0.0286, 451 structure factors, 16 variables. The palladium and cadmium atoms build up a three-dimensional [PdCd2] network (281 - 283 pm Pd-Cd; 298 - 335 pm Cd-Cd) in which the neodymium atoms fill cavities. They are connected to the [PdCd2] network via shorter Nd-Pd bonds of 286 pm.

Magnetoelectric properties of Tb0.27−xDy0.73−yYx+yFe2/PVDF composites

Synthesis by arc melting, and the structural and electric properties of yttrium-diluted Tb0.27−xDy0.73−yYx+yFe2 intermetallics were studied by X-ray diffraction (XRD) and four-probe dc electrical measurements. XRD analysis (300K) shows that all samples crystallize in a cubic, Fd3m, MgCu2-type structure. The lattice parameter increases along with the yttrium content. Electrical resistivity for the Tb0.27−xDy0.73−yYx+yFe2 intermetallic series was measured in a temperature range of 15–1100K. The parameters involved in the dependence of resistivity on temperature were determined. Residual, phonon and magnetic resistivity were separated from the measured electrical resistivity using both the Matthiesen formula and the Bloch–Grűneisen formula. Curie temperatures of the compounds were obtained from the magnetic resistivity curves. Magnetoelectric composites containing magnetostrictive Tb0.27−xDy0.73−yYx+yFe2 grains in a PVDF matrix were prepared. All the composites were characterized by scanning electron microscope observations. The measurements carried out at room temperature as a function of the external DC magnetic field and frequency of the sinusoidal AC modulation magnetic field reveal a distinct magnetoelectric effect of the Tb0.27−xDy0.73−yYx+yFe2/PVDF composites.

Study on the Preparation Technique and Magnetostriction of Sinter Tb&lt;sub&gt;0.7&lt;/sub&gt;Pr&lt;sub&gt;0.3&lt;/sub&gt;Fe&lt;sub&gt;1.80&lt;/sub&gt; Alloy

Mechanical alloying (MA) and subsequent solid sintering process was used to prepare the Pr-containing pseudobinary Tb0.7Pr0.3Fe1.80alloys. The structural and magnetoelastic properties were in comparative investigated by means of x-ray diffraction and a standard strain technique for sinter and composite samples. The high Pr-content (Tb,Pr)Fe2Laves phase with MgCu2-type structure for the composition Tb0.7Pr0.3Fe1.80 were synthesized by MA plus annealing at 500 °C.

Magnetostriction and Hysteresis of Tbdyhofe&lt;sub&gt;1.95 &lt;/sub&gt;Alloys

The crystal structure, Curie temperatures, spin reorientation temperature, magnetocrystalline anisotropy constant and magnetostriction of TbDyHoFe1.95 alloys with composition formulation (1-y)Tb0.36Dy0.64Fe1.95+yTb0.20Dy0.22Ho0.58Fe1.95 (0≤y≤1) were investigated. X-ray diffraction patterns demonstrate the TbDyHoFe1.95 alloys possess MgCu2-type cubic Laves structure. The Curie temperature Tc decreases slightly from 381 °C for Tb0.36Dy0.64Fe2 to 379 °C for y=0.3, 375°C for y=0.4 and 373°C for y=0.5. The spin reorientation temperature Tr increases from -94 oC for Tb0.36Dy0.64Fe2 to -70°C for y=0.3 and -51oC for y=0.5. The magnetocrystalline anisotropy constant K1 decreases with increasing y value. The magnetostriction was examined under applied magnetic field H (0

Structure and magnetostriction of Tb1−xNdx(Fe0.8Co0.2)1.93 alloys

The structure, magnetization and magnetostriction of Tb1−xNdx(Fe0.8Co0.2)1.93 (0 ≤ x ≤ 1.0) alloys have been investigated by means of X-ray diffraction, a vibrating sample magnetometer and a standard strain technique. X-ray diffraction (XRD) analysis shows that the alloys possess predominantly the cubic Laves phase with a MgCu2-type structure for x ≤ 0.6. The lattice parameter of the Laves phase increases with increasing Nd content and obeys the linear Vegard's law. The easy direction of magnetization (EMD) is observed toward <111> when 0 ≤ x ≤ 0.6, accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients λ111. The saturation magnetization MS at room temperature (RT) decreases with increasing Nd content when 0 ≤ x ≤ 0.5, then increases with further increasing x for x ≥ 0.6. The linear anisotropic magnetostriction λa (= λ||– λ⊥) at RT decreases initially with increasing x when 0 ≤ x ≤ 0.4, then increases with a further increasing x and exhibits a peak in the range of 0.4 < x < 1.0.

Structural properties and magnetic phase transition in HoNi2Mn (57Fe)

The structural and magnetic properties of HoNi2Mn(57Fe) have been investigated. The 57Fe-doped HoNi2Mn compound crystallizes in the MgCu2-type structure with Fd-3m space group similar to HoNi2 and HoMn2. HoNi2Mn(57Fe) exhibits ferrimagnetic ordering below a Curie temperature of TC ∼ 60 K—significantly higher than the corresponding values for HoNi2 (TC = 15 K) and HoMn2 (TC = 24 K)—with analyses of dc magnetization and ac susceptibility results confirming that the magnetic transition at TC is second order. The Mössbauer spectra above TC are described well by two sub-spectra representing the 8a and 16d sites while below TC the spectra have been fitted using a site model comprising three sub-spectra. The Debye temperature, θD = 190(20) K, has been determined.

Preparation and Magnetostriction of Epoxy-Bonded Pr(Fe&lt;sub&gt;0.4&lt;/sub&gt;Co&lt;sub&gt;0.6&lt;/sub&gt;)&lt;sub&gt;1.93&lt;/sub&gt; Composites

The magnetostrictive Pr(Fe0.4Co0.6)1.93alloy with MgCu2-type structure, and its 0-3 and pseudo 1-3 type epoxy-bonded composites were fabricated by curing without and with a magnetic field. The structural, magnetic and magnetoelastic properties were investigated by means of x-ray diffraction, a vibrating sample magnetometer and a standard strain technique. The 0-3 type composite has a larger magnetostriction than the 1-3 composite has, which can be ascribed to the easy magnetization direction (EMD) not lying along direction.