Preparation And Magnetic Properties Of Light-rare Earth RFe₂ Magneto-elastic Materials

The rare-earth transition-metal（RE-TM）compounds,(Tb_0.3Dy_0.7)_1-x(Pr_0.5Nd_0.5)_xFe_1.93 and（Pr/Nd）-doped（Tb,Ho）（Fe,Co）_1.93,were prepared by high-vacuum arc-melting and subsequent annealing.The epoxy bonded 1-3 type and 0-3 type Tb_xHo_0.9-xNd_0.1(Fe_0.8Co_0.2)_1.93 composites were also fabricated by curing with and without a magnetic field,respectively.The phase structure,magnetic and magnetostrictive properties were investigated by X-ray diffraction（XRD）,vibrating sample magnetometer（VSM）,A.C.initial susceptibility tester and static standard strain gauge.In the(Tb_0.3Dy_0.7)_1-x(Pr_0.5Nd_0.5)_xFe_1.93 polycrystalline alloy system,the annealing temperature and the contents of light rare earth Pr/Nd were studied,focusing on the formation of the phase structure and magnetic properties.The analysis of XRD patterns shows that introduction of Pr/Nd elements does not change the MgCu₂-type structure of the cubic Laves phase and the easy magnetization direction（EMD）.In addition,the introduction of Pr/Nd elements decreases the magnetocrystalline anisotropy and improves the low-field magnetoelastic properties.The EMD lies along the <111> axis,accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients λ111.When x = 0.12,the alloy obtains the good magnetoelastic properties: the content around the anisotropic compensation point,a large spontaneous magnetostriction coefficient λ111（¹710 ppm）,a high low-field magnetostriction la（³14 ppm/1 kOe）and a giant saturation magnetostriction lS（¹060 ppm）,which show that this material is a promising candidate for magnetostriction applications.In the Tb_xHo_0.8-xPr_0.2(Fe_0.8Co_0.2)_1.93 alloys system,a small amount of Co（20%）substitution of Fe improves the formation of single Laves phase.The lattice parameters（a）,Curie temperature（TC）and saturation magnetization（MS）linearly increase with increasing the Tb content,and obeys the linear Vegard’s law.At room temperature,the easy magnetization direction（EMD）rotates from <100> axis（x ≤ 0.10）to the <111> axis（x ≥ 0.15）with increasing Tb content,accompanied with a large rhombohedral distortion with large spontaneous magnetostriction coefficients λ111.The analysis of XRD,EMD and magnetostriction shows that Tb_xHo_0.8-xPr_0.2(Fe_0.8Co_0.2)_1.93 is an anisotropy compensation system,and the critical compensation point is realized around x = 0.15.The good magnetoelastic properties is obtained that la is realized to be 510 ppm/ 3 kOeAs for the Tb_xHo_0.9-xNd_0.1(Fe_0.8Co_0.2)_1.93 alloy system,the 1-3 and 0-3 typeparticulate composites were produced by embedding and aligning alloy particles with epoxy matrix in the presence and absence of the magnetic field conditions.The magnetic properties and magnetoelastic properties of the composites were studied by changing the composition,particle volume fraction and macroscopic structure of the composites.At room temperature,the EMD lies along <111> direction and the anisotropic compensation point was found to be near x = 0.25.An enhanced magneto-elastic effect and a large low-field-magnetostriction la,as high as 430 ppm at 3 kOe,was obtained for 1-3 type Tb_0.25Ho_0.65Nd_0.1(Fe_0.8Co_0.2)_1.93 composite with 30 vol% alloy particles.