Electrical properties of ferromagnetic Ni2MnGa and Co2CrGa Heusler alloys

Specific features of the electrical resistance of half-metallic ferromagnetic alloys Co2CrAl and Co2CrGa

“…It resembles the one of manganese near the Néel point and is explained in [8] by superposition of the phonon and magnon contributions to resistivity, when a linear increase in ρ ph (T) is superimposed by a sharp decrease of the magnetic contribution owing to disappearance of spontaneous magnetization. As was derived in [8], in the mean field approximation, (4) According to [4], similar situation takes place in Co 2 CrGa half metallic ferromagnet. The spontaneous magnetization M s 0 vanishes at T T C .…”

“…In [3,4], the specific behavior of ρ(T) in half metallic ferromagnets was attributed to both the scat tering mechanisms usually characterized by the relax ation time τ or the mean free path length l = 1/τ of conduction electrons and the specific electronic band structure of the alloys, i.e., the number n of charge car riers. Consequently, the conductivity σ = 1/ρ in the simplest case is determined by the well known relation (1) where e is the absolute value of the electron charge and m* is the effective mass of charge carriers.…”

“…Taking into account a rather high resistivity of half metallic ferromagnets, the total conductivity should be described by the expression (2) Naturally, the band gap contribution to the resistivity ρ ↓ is shunted at low σ, i.e., when σ ↑ ӷ σ ↓ . Conse quently, according to [3,4], the specific behavior of ρ(T) of half metallic ferromagnets is determined by the relation between the conductivities of two chan nels. When σ ↑ is low and comparable with σ ↓ , a con siderable role is played by the band gap contribution to the total resistivity.…”

“…2, the residual resistivity of the Co 2 CrAl and Co 2 CrGa alloys is ρ 0 ~ 1.5 and 1.3 μΩ m, respectively. In addition, the ρ(T) curves of these half metallic fer romagnets near the Curie point T C are characterized by pronounced features: a sign change of the resis tance temperature coefficient of the Co 2 CrAl alloy [2, 3] and a peak type anomaly in Co 2 CrGa [4]. The high values of ρ 0 and the negative resistance temperature coefficient of Co 2 CrAl at T < T C were attributed in [5,6] to the presence of a mixture of metallic and semi conductor phases in the samples.…”

Temperature Dependences of the Electrical Resistivity on the Heusler Alloy System Ni2MnGa1−xFex

“…Many authors fitted Equation (1) to their experimental data for many Heusler alloys. [17][18][19][20][21][22][23]. Table 1 gives the ρ0, a, and b values, the validity range of fit, and TC values of Ni2MnGa1-xFex.…”