Studies of bulk MgCu2-type rare-earth iron compounds with Laves phase are reviewed. The relationship between magnetostriction and structural distortion and the consequent crystallographic method for measuring magnetostriction are introduced at first. Then we review recent progress in understanding bulk magnetostrictive Laves phase materials, especially the magnetostriction and the minimization of the anisotropy of the light rare-earth Pr- and Sm-based compounds. Finally, a summary and outlook for this kind of compounds are presented.
The linear elasticity was studied in a martens- tic alloy NisoMn25Ga9Cu16. A 0.4 % linear elastic strain is btained in the polycrystalline sample under compressive stress of 745 MPa. The elastic modulus is 186 GPa. The obtained linear elastic strain and elastic modulus are much higher than that of ternary Ni-Mn-Ga martensitic alloys.~.bstract The linear elasticity was studied in a martens- tic alloy NisoMn25Ga9Cu16. A 0.4 % linear elastic strain is ~btained in the polycrystalline sample under compressive stress of 745 MPa. The elastic modulus is 186 GPa. The obtained linear elastic strain and elastic modulus are much higher than that of ternary Ni-Mn-Ga martensitic alloys.
In order to demonstrate that light rare-earth(RE)dopants with strong magnetocrystalline anisotropy, whose net moment couples are antiparallel to those of iron, can also induce giant magnetostriction in Gafenol, a light RE element Sm was selected as the third element to dope into FeGaalloy.(FeGa)Sm(0≤x≤0.42) ribbons were prepared by melt spinning. The increase of the lattice parameters and saturation magnetization indicates that some Sm atoms enter the A2 matrix substitutionally. Doping the FeGaribbons with the light RE Sm element drastically improves the magnetostriction. Perpendicular magnetostriction value of λ=-5*10is achieved in(FeGa)Sm. It is confirmed that the stronger local magnetocrystalline anisotropy induces larger enhanced magnetostrictions. The greatly enhanced magnetostriction is somehow related to the local microstrains induced by the RE dopants. It is likely that the RE-induced defects in the(FeGa)REribbons function in the similar way as the Ga–Ga pair defects in the undoped Fe–Ga alloys.
The microstructure and magnetostrictive properties were investigated in the Tb doped Fe83Ga17-xTbx(x = 0.05, 0.10, 0.20, 0.30, 0.40, 0.50) bulk rods prepared by melt rapidly quenching. The partial solid solubility of Tb in the Fe-Ga matrix was preliminary detected by the lattice parameters and SEM observation. The matrix keeps A2 structure and the second phase appears surround the grain boundary as x C 0.1. h100 i preferred orientation is also observed for x = 0.1 sample along the axis of the quenched rod. The saturation magnetostriction first increases and maximum value reaches at x = 0.1, and then decreases with Tb addition increasing. The initial increase of the magnetostriction should be associated with the partial solution of Tb in the matrix, the maximum value at x = 0.1 should be attributed to the h100 i preferred orientation, and the decrease of the magnetostriction is correlated with the appearance of the second phase along the grain boundary.
Studies on Co-doped Ni–Mn–Ga ferromagnetic shape memory alloys(FSMAs)have been quite active topics in recent years.Unlike previous reports where the amount of Co doping was generally less than 8 at%,in this work Ni_(55-x)Co_(x)Mn_(20)Ga_(25)(8.5≤x≤11.0)alloys were studied with high Co doping.Unusual effects of both composition and magnetic field on phase transitions were observed.With the increase in substitution of Co for Ni,the magnetic transition temperatures increase gradually but the martensitic transformation temperature decreases quite sharply.In particular,the average decrease in the martensitic transformation temperatures is up to 100 K which is nearly twice that in the case of Co content of less than 8 at%.Further,under an applied magnetic field ranging from 0.03 to 0.60 T,abnormal stabilization of a martensite phase with lower magnetization was monitored.Magnetic entropy change of 1.6 J·kg^(−1)·K^(−1)was induced at the martensitic transformation of Ni46.5Co8.5Mn20Ga25 alloy by an applied field of 1 T.The magnetic contributions,including the magnetocrystalline anisotropy and the Zeeman energy,to the thermodynamics of the martensitic transformation are considered to understand the observed unusual phenomena.This work results in new insights into the understanding of Co-doped Ni–Mn-based ferromagnetic shape memory alloys.
Ni30Cu20Mn37+xGa13-x(x = 0–4.5) alloys were studied with the phase transformation and mechanical properties. With the increase of Mn content, the martensitic transformation temperatures increase and the Curie temperature decreases. Simultaneously, the room temperature microstructure evolves from single phase of austenite to dual phases containing martensite and precipitation. Both the ductility and the strength of the polycrystalline alloys are significantly improved by the precipitation. Coupled magnetostructural transition from weak magnetic martensite to ferromagnetic austenite is obtained in both single-phase and ductile dual-phase alloys.