X.M. Jin

Microstructure and magnetostriction of (Dy0.7Tb0.3)1−xPrxFe1.85 and (Dy0.7Tb0.3)0.7Pr0.3Fey alloys

The structure, Curie temperature, and magnetostriction of R(1-x)Pr(x)Fe(1.85) and R(0.7)Pr(0.3)Fe(y) (R = Dy0.7Tb0.3, x less than or equal to 0.5, 1.55 less than or equal to y less than or equal to 1.85) alloys were investigated. The matrix of R(1-x)Pr(x)Fe(1.85) alloys is the MgCu2-type cubic (Dy,Tb,Pr) Fe-2 and the second phase was found to be (Dy,Tb,Pr) Fe-3 when x less than or equal to 0.3. When x>0.4, (Dy,Tb,Pr) Fe-3 is the main phase with the PuNi3-type structure and (Dy,Tb,Pr) Fe-2 becomes the minority phase. In the range of 0.3 1.55, which increased with increasing y. When y = 1.55, the alloy is essentially single phase with the MgCu2-type cubic structure. The lattice parameter of (Dy,Tb,Pr) Fe-2 compound for R(1-x)Pr(x)Fe(1.85) alloys increases slowly with increasing x when x less than or equal to 0.3, and sharply increases when x>0.3. The Curie temperature of the alloys decreases steadily with increasing Pr content. The magnetostrictions of R(1-x)Pr(x)Fe(1.85) and R(0.7)Pr(0.3)Fe(y) alloys decrease with increasing Pr content and Fe content, respectively. The largest magnetostriction at room temperature was found in the alloy R(0.7)Pr(0.3)Fe(1.55) (1480 x 10(-6) at H = 796 kA/m)

Effect of boron on structure and magnetic properties of magnetostrictive compound Dy0.7Pr0.3Fe2

Crystal structure, magnetic properties and magnetostriction of Dy0.7Pr0.3(Fe1-xBx)(2) (0less than or equal toxless than or equal to0.20) have been investigated by means of x-ray diffraction, ac initial susceptibility, a vibrating sample magnetometer, and a standard strain technique. The matrix of Dy0.7Pr0.3Fe2 alloy consists of (Dy,Pr)Fe-2 phase with a cubic MgCu2-type structure and some amount of (Dy,Pr)Fe-3 phase with a rhombohedral PuNi3-type structure. The introduction of boron effectively restrains the emergence of the iron-rich phase and thus decreases the amount of (Dy,Pr)Fe-3 phase. Dy0.7Pr0.3(Fe1-xBx)(2) alloy with x=0.05 contains small amount of (Dy,Pr)(Fe,B)(3) phase, and those with x=0.10 and x=0.15 are essentially of a single (Dy,Pr)(Fe,B)(2) phase. An unidentified minor phase appears when x=0.20. The lattice parameter of (Dy,Pr)(Fe,B)(2) phase decreases monotonically with the boron substitution up to x=0.20, indicating that the boron atoms occupy the substitutional sites. The Curie temperature for (Dy,Pr)(Fe,B)(2) phase obviously increases compared with the boron free one. The saturation magnetization at room temperature increases with increasing boron content for the alloys studied, suggesting that the partial boron substitution is beneficial to the increment of the exchange interactions in the Dy0.7Pr0.3Fe2 system. The increment of the magnetization originates from the decrement of iron content, because the Fe moment that aligns antiparallel with the Dy moment almost keeps constant in this system. Boron substitution for iron increases the lattice distortion and anisotropy, thus causes the decrease of the linear magnetostriction lambda(a)=lambda(parallel to)-lambda(perpendicular to) at the room temperature

Giant magnetoresistance in Co-Cu-Ni granular ribbons

We have systematically investigated the structural, magnetic and transport properties of as-quenched and annealed Co20NixCu80-x (0 less than or equal to x less than or equal to 20) granular alloys prepared by melt spinning. The microstructure of granular ribbons of Co-Ni-Cu shows a matrix in which nanoparticles of Co-Ni are well distributed, very different from that of granular ribbons of Ca-Cu in which fun-grown Co microparticles are embedded in a Cu matrix. The phase segregation in the Co-Ni-Cu granular ribbons is not a pure nucleation and growth process as in the Co-Cu granular ribbons, but also not purely due to spinodal decomposition. In contrast to the ribbons with high Ni content, the low-Ni-content ribbons show an increase in magnetoresistance (Delta R/R congruent to 6.2% at 300 K for Co20Ni5Cu75, which is larger than in as-quenched and annealed Co-Cu ribbons.

Structure and magnetostriction of R(Fe1-xMnx)(1.85) alloys (R=Dy0.6Tb0.3Pr0.1)

The structure, Curie temperature and magnetostriction of R(Fe1-xMnx)(1.85) alloys (x=0-0.3) were investigated. These alloys are essentially single phase with a cubic Laves structure. The lattice constant increases steadily and the Curie temperature decreases linearly with increasing Mn content. The largest magnetostriction occurs at about x=0.05.

Magnetostriction and anisotropy compensation composition of Dy0.9-xTbxPr0.1Fe1.85, Dy1-xTbx(Fe0.9Mn0.1)(1.8) and Dy0.9-xTbxPr0.1(Fe0.9Mn0.1)(1.8) alloys

The structure, Curie temperatures and magnetostriction of the alloys Dy0.9-xTbxPr0.1Fe1.85, Dy1-xTbx(Fe0.9Mn0.1)(1.8) and Dy0.9-xTbxPr0.1(Fe0.9Mn0.1)(1.8) have been investigated, These alloys are essentially single phase with cubic Laves structure. The lattice parameters and Curie temperatures increase steadily with increasing Tb content, The Tb dependence of the magnetostriction in various applied fields for polycrystalline Dy0.9-xTbxPr0.1Fe1.85 and Dy0.9-xTbxPr0.1(Fe0.9Mn0.1)(1.8) alloys exhibits peaks at x = 0.25 and 0.3, respectively. From a comparison of Dy1-xTbxFe2 and Dy1-xTbx(Fe0.9Mn0.1)(2), it appears that the addition of Pr shifts the magnetocrystalline anisotropy compensation composition to lower Tb contents.

Beneficial effect of nonmagnetic Y on magnetic properties due to the enhancement of exchange coupling in nanocomposite (Nd,Y)2Fe14B/α–Fe magnets

We have studied the nanocomposite magnets with nominal compositions of Nd8-xYxFe88B4 (x=0-4.0) by mechanical milling techniques and subsequent heat treatment. We find that there exists the beneficial effect of nonmagnetic Y substitution for magnetic Nd on magnetic properties in nanocomposite magnets. The extension of the exchange coupling length, due to a decrease of the anisotropy of the hard-magnetic phase, results in that more soft-magnetic grains participate well in the exchange coupling, improving the magnetic properties of the nanocomposite magnets

Structure and magnetostriction of (Dy0.65Tb0.25Pr0.1)(Fe1−xAlx)3 alloys

The structure, Curie temperature and magnetostriction of (Dy0.65Tb0.25Pr0.1)(Fe1-xAlx)(3) (0 less than or equal to x less than or equal to 0.30) alloys were investigated using optical microscopy, X-ray diffraction, electron probe microanalysis, vibrating sample magnetometer and standard strain gauge techniques. It was found that these alloys are multiphase. When x less than or equal to 0.10, the main phase possesses the PuNi3-type rhombohedral structure and becomes CeNi3-type hexagonal when x>0.25. When 0.10<x less than or equal to 0.25, both structures coexist. A minor phase (Dy,Tb,Pr)(6)(Fe,Al)(23) exists in all alloys, which increases with increasing Al content. The Curie temperature and the room-temperature magnetostriction of the (Dy0.65Tb0.25Pr0.1)(Fe1-xAlx)(3) alloys decrease with increasing Al substitution for Fe.

Microstructure and magnetostriction for (Dy0.65Tb0.25Pr0.1)(Fe1-xAlx)(1.8) alloys

The microstructure, Curie temperature and magnetostriction of R(Fe1-xAlx)(1.8) alloys (R=Dy0.65Tb0.25Pr0.1, x less than or equal to 0.3) have been investigated using optical microscopy, x-ray diffraction, transmission electron microscopy, electron probe microanalysis, positron annihilation technique, vibrating sample magnetometer, and standard strain gauge technique. It was found that the alloys are essentially single phase up to x=0.30. The defects in R(Fe1-xAlx)(1.8) decrease with increasing Al content when x less than or equal to 0.1. The magnetostriction of the alloys decreases with increasing Al content in high applied magnetic fields, but it exhibits a peak when x=0.05 in low applied magnetic fields (H less than or equal to 160 k A/m)

Crystallographic and magnetic properties of the quaternary rare-earth-transition-metal boron nitrides R2Fe14BN0.1 (R = Nd and Sm)

Quaternary rate-earth-transition-metal boron nitrides, R2Fe14BN0.1 (R = Nd and Sm), have been synthesized by ate melting. The bond of boron nitride (BN) can be broken by are melting to allow combination with rare-earth and transition-metal atoms. The structure and magnetic properties of these quaternary compounds have been studied by means of x-ray diffraction, neutron diffraction, and alternating-current initial-susceptibility and magnetization measurements. The R2Fe14BN0.1 (R = Nd and Sm) compounds have the tetragonal Nd2Fe14B-type structure with space group P4(2)/mnm,. The Curie temperature and magnetic anisotropy of the compound Nd2Fe14B are slightly enhanced by introducing nitrogen into the lattice of Nd2Fe14B. The spin-reorientation temperature of Nd2Fe14BN0.1 is the same as that of Nd2Fe14B.

Effect of substitution of Gd for Nd on the magnetic properties of Nd2Fe14B-α-Fe nanocomposite magnets

We have studied the effect of substitution of Gd for Nd on the exchange coupling in nanocomposite Nd2Fe14B–α-Fe magnets, and compared it with the substitution of Y and Sm for Nd. An enhancement of the exchange coupling is observed, due to the increased exchange correlation length originating from the decrease of the magnetocrystalline anisotropy of the hard-magnetic phase. The soft grains are pinned to the hard magnet grains at the interfaces by the exchange interaction, and more soft-magnetic grains participate in the exchange coupling.