J.J. Liu

Enhanced magnetostrictive effect in epoxy-bonded TbxDy0.9-xNd0.1(Fe0.8Co0.2)(1.93) pseudo 1-3 particulate composites

The spin configuration and spontaneous magnetostriction λ111 of TbxDy0.9−xNd0.1(Fe0.8Co0.2)1.93 (0.20 ≤ x ≤ 0.60) alloys have been investigated. The easy magnetization direction (EMD) at room temperature was observed towards the 〈111〉 axis when 0.40 ≤ x ≤ 0.60, accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients λ111, which increases from 1640 ppm for x = 0.40 to 1900 ppm for x = 0.60. The strong 〈111〉-oriented pseudo 1–3 particulate composite was fabricated by embedding and aligning particles in a passive epoxy matrix under an applied magnetic field. An enhanced magnetostrictive effect, the large low-field magnetostriction, λa, as high as 480 ppm at 3 kOe, was obtained for the sample of x = 0.40, in an excess of 75% of its polycrystalline alloy although it only contains 27 vol. % alloy particles. This enhanced effect can be attributed to its low magnetic anisotropy, anisotropic magnetostrictive nature (e.g., λ111 ≠ λ100, 〈111〉EMD), chain structure, and the 〈111〉-...

Structure and Magnetic Properties of MnAl/α-Fe Nano-Composite Powders Prepared by High-Energy Ball Milling

Novel nano-composite powders composed of hard-magnetic Mn54Al46 and soft-magnetic α-Fe were prepared by high-energy ball milling. The effect of α-Fe and preparation conditions on the structure and magnetic properties of the composite powders has been investigated. The ε-MnAl transforms to γ-MnAl, τ-MnAl, and β-phase under ball milling and annealing. The saturation magnetization and coercivity of the two-phase samples decrease with increasing temperature for the τ-phase decomposes at elevated temperatures. With increasing iron content, the coercivity decrease first and then increase up to 0.33 T when the Fe content is 10 wt%. Further addition of the magnetically soft iron phase would result in a decrease of the coercivity.

Magnetoelastic properties of epoxy resin based TbxHo0.9−xNd0.1 (Fe0.8Co0.2)1.93 particulate composites

Abstract TbxHo0.9−xNd0.1 (Fe0.8Co0.2)1.93 (0 ⩽ x ⩽ 0.40) particulate composites were prepared by embedding and aligning alloy particles in an epoxy matrix with and without a magnetic curing field. The magnetoelastic properties were investigated as functions of composition, particle volume fraction and macroscopic structure of the composite. The magnetic anisotropy compensation point was found to be around x = 0.25, where the easy magnetization direction (EMD) at room temperature was detected lying along ⟨ 1 1 1 ⟩ axis. The composite with ⟨ 1 1 1 ⟩ preferred orientation and pseudo-1-3 type structure was prepared under an applied magnetic field of 12 kOe. An enhanced magnetoelastic effect and large low-field magnetostriction λa, as high as 430 ppm at 3 kOe, were obtained for Tb0.25Ho0.65Nd0.1 (Fe0.8Co0.2)1.93 composite rod. The value of λa was of 72 % of its polycrystalline alloy (~595 ppm/3 kOe) although it only contained 30 vol.% of the alloy particles. This enhanced effect can be attributed to the larger λ111 (as compared to λ100), low magnetic anisotropy, easy magnetization direction (EMD) along the ⟨ 1 1 1 ⟩ axis and ⟨ 1 1 1 ⟩-textured orientation of the alloy particles as well as the chain-like structure of the composite. The good magnetoelastic properties of the composite, in spite of the fact that it contained only 30 vol.% of the alloy particles with light rare-earth Nd element in the insulating epoxy, would make it a potential material for magnetostriction application.

Magnetic properties of single-phase MnBi grown from MnBi49 melt

The single-phase NiAs-type MnBi, embedded in Bi matrix, was grown from homogeneous MnBi49 melt at low temperatures to prevent the formation of Mn1.08Bi. An abrupt magnetization change was observed at ∼240 K. The origin of this change was ascribed to the movement of the Mn atoms between the regular sites and the interstitial sites in the MnBi lattices. The splitting of the x-ray photoelectron lines of MnBi indicates the presence of two binding states of Mn atoms, one of which was ascribed to interstitial Mn atoms. A large coercivity up to 1.79 T at 400 K was observed in the as-grown bulk isotropic MnBi alloys.

Study on the Preparation Technique and Magnetostriction of Sinter Tb0.7Pr0.3Fe1.80 Alloy

Mechanical alloying (MA) and subsequent solid sintering process was used to prepare the Pr-containing pseudobinary Tb0.7Pr0.3Fe1.80 alloys. 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)Fe2 Laves phase with MgCu2-type structure for the composition Tb0.7Pr0.3Fe1.80 were synthesized by MA plus annealing at 500 °C.

Preparation and Magnetostriction of Epoxy-Bonded Pr(Fe0.4Co0.6)1.93 Composites

The magnetostrictive Pr(Fe0.4Co0.6)1.93 alloy 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.

Magnetic Properties of Sm-Fe-N Prepared by Melt-Spun in Liquid N2 and High Gas Pressure Nitrogenation

Sm-Fe-N was prepared by melt-spun Sm-Fe with liquid-N2-cooled copper wheel and nitrogen absorption under N2 gas pressures up to 25 MPa. The structure and magnetic properties of the Sm-Fe-N prepared under varied temperatures, N2 pressures and nitrogen absorption time have been investigated systematically. The liquid N2 melt-spun process improves the homogeneity of the samples while the high N2 pressure increases the efficiency of the nitrogenation process. The Sm-Fe-N decomposes under 25 MPa N2 at temperatures above 743 K.

Structure and Magnetic Properties of Sm-Fe-N Prepared by Nitriding High Purity Sm2Fe17 Grown from Sm-Rich Melt

We report on a novel method for preparation of high purity Sm2Fe17 phase by removing the liquid impurity phase from the Sm-rich precursor at high temperatures. With decreasing Sm addition, the percentage of liquid phase left as impurity is decreasing. Nitrogen absorption to the Sm2Fe17 powders results in a complete formation of Sm2Fe17N3, which shows a weak disproportionation reaction at 773 K. The magnetic performance of the Sm2Fe17N3 from precursors with different Sm content is improving with decreasing Sm content.

Magnetostriction of Epoxy-Bonded Tb0.22Dy0.48Pr0.3(Fe0.9B0.1)1.93 Composites

The magnetostrictive Tb0.22Dy0.48Pr0.3(Fe0.9B0.1)1.93 alloy, 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 in investigated by means of x-ray diffraction, an alternating gradient magnetometer and a standard strain technique. The easy magnetization direction (EMD) is lying along <111> direction at room temperature. The 1-3 type composites has a larger magnetostriction than the 0-3 composite has, which can be attributed to the <111>-textured orientation and the chain structure.

Structure and Magnetostrictive Properties of Tb0.2Pr0.8(Fe0.4Co0.6)1.9Bx Alloys

Crystal structure and magnetostrictive properties of Tb0.2Pr0.8(Fe0.4Co0.6)1.9Bx alloys have been investigated by means of x-ray diffraction and a standard strain technique. The matrix of Tb0.2Pr0.8(Fe0.4Co0.6)1.9 alloy consists of (Tb,Pr)(Fe,Co)2 phase with a cubic MgCu2-type structure and some amount of (Tb,Pr)(Fe,Co)3 phase with a PuNi3-type structure. The introduction of boron effectively restrains the emergence of the iron-rich phase, which can occupy either the substitutional or interstitial site in this alloy system. The single Laves phase can be obtained for the high Pr-content Tb0.2Pr0.8(Fe0.4Co0.6)1.9Bx alloys with 0.05< x ≤0.15, which have improved magnetostrictive properties as compared to the boron free material.