title: Magnetic anisotropy in Ni-Fe-Ga-Co ferromagnetic shape memory alloys in the single-variant state.
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.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Morito
authors.forename: A
authors.initials: A
authors.lastname: Fujita
authors.forename: K
authors.initials: K
authors.lastname: Oikawa
authors.forename: K
authors.initials: K
authors.lastname: Fukamichi
authors.forename: R
authors.initials: R
authors.lastname: Kainuma
authors.forename: T
authors.initials: T
authors.lastname: Kanomata
authors.forename: K
authors.initials: K
authors.lastname: Ishida