ABSTRACT
The effects of the addition of Co on the magnetic anisotropy in Ni(55-x)Fe(18)Ga(27)Co(x) (x = 1-6) single-variant ferromagnetic shape memory alloys have been investigated. By the addition of Co from 1 to 6 at.%, the Curie temperature T(C) is increased from 318 to 405 K, keeping the martensitic transformation temperatures above room temperature. As a result, the value of the uniaxial magnetic anisotropy constant |K(u)| at 300 K increases with increasing x of the Co concentration and the martensite phase of Ni(49)Fe(18)Ga(27)Co(6) exhibits a relatively high value of |K(u)| = 1.15 × 10(5) J m(-3) at 300 K. With increasing Co concentration, on the other hand, the c axis changes from the magnetic easy axis to the hard axis at 4.2 K, that is, the sign of K(u) is reversed from positive to negative between 2 and 3 at.% Co. Furthermore, K(u) in Ni(53)Fe(18)Ga(27)Co(2) is positive below 100 K and negative above 100 K up to T(C), reducing the magnetic anisotropy around 200 K. From the present results, it is evident that the magnetic anisotropy of Ni(55-x)Fe(18)Ga(27)Co(x) (x = 1-6) single-variant ferromagnetic shape memory alloys is very sensitive to Co concentration and also temperature.
ABSTRACT
The magnetic anisotropy and the magnetic-field-induced strain (MFIS) in a single-variant Co(47.5)Ni(22.5)Ga(30.0) ferromagnetic shape memory alloy (FSMA) have been investigated. From the magnetization curves for the single crystal, the hard c-axis was confirmed, and the uniaxial magnetic anisotropy constant K(u) at 300 K was evaluated to be -1.07 × 10(6) erg cm(-3) for the single-variant Co(47.5)Ni(22.5)Ga(30.0) martensite phase. The magnitude of compressive shear stress for the variant rearrangement was estimated to be 6.0-7.5 MPa from the stress-strain curves. An assisted stress τ(assist) of 6.0 MPa was applied before applying a magnetic field, and then a magnetic stress τ(mag) of 0.3 MPa was added. As a result, a large MFIS of about 7.6 % was obtained at room temperature in the martensite phase of the single-variant Co(47.5)Ni(22.5)Ga(30.0).
