Experimental observation of anomalies in the electrical, magnetic, and galvanomagnetic properties of cobalt-based Heusler alloys with varying transition elements

Abstract

The residual resistivity, Hall effect, and magnetization of Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys were considered at T = 4.2 K and in fields up to 100 kOe. It is shown that as the number of valence electrons z ranges from 26 to 32, significant changes in the residual resistivity ρ0, magnetization Ms, sign and magnitude of the normal R0 and anomalous RS Hall effect coefficients are observed during the transition from Co2TiSi to Co2NiSi. It is established that there is a clear correlation between the values ρ0, R0, RS and Ms, depending on the number z, which can be associated with the appearance of a half-metal ferromagnetic state and/or spin gapless semiconductor. As z changes, the anomalous Hall effect coefficient has a power-law dependence on the residual electrical resistivity with an exponent of k = 3.1, which diverges with existing theories but agrees well with the experimental data obtained earlier for similar half-metallic ferromagnetic Heusler alloys.

Peculiarities of Electronic Transport and Magnetic State in Half-Metallic Ferromagnetic and Spin Gapless Semiconducting Heusler Alloys

“…5b and 5c), the maximum (minimum) of the residual resistivity corresponds to the minimum (maximum) of magnetization and the maximum (minimum) of the normal Hall coefficient. As already noted in [24], the number of valence electrons z is a rather crude characteristic which does not represent properly peculiarities of a particular Table 3. The saturation magnetization M S , the normal R 0 and anomalous R S Hall coefficients, the residual electroresistivity  0 , the current carrier concentration n, mobility μ and the Curie temperatures compound in terms of its electronic band structure features.…”

“…As already noted in [24], the number of valence electrons z is a rather crude characteristic which does not represent properly peculiarities of a particular compound in terms of its electronic band structure features. The density of electron states N(E) at the Fermi level E F could be such a parameter.…”

Unusual Kinetic Properties of Usual Heusler Alloys

“…~ 10 22 -10 23 cm -3 , the magnetic state, as a rule, is ferromagnetic with sufficiently large magnetization values up to 6 µB/f.u. [48,58,59].…”

Magnetic and thermal properties of alloys close in composition to the spin gapless semiconductor Mn2CoAl

“…These alloys have the same general formula X 2 YZ, where X and Y are 3d metals, and Z are s, p element, but a different crystal structure: L2 1 of the Cu 2 MnAl-type (full) and X a of the Hg 2 CuTi-type (inverse). According to many ab initio calculations, alloys with the L2 1 structure are of interest as materials such as half-metallic ferromagnets, [15][16][17][18] and inverse alloys are interesting as gapless semiconductors with ferrimagnetic properties or spin gapless semiconductors (SGS). 14,19 Calculations show that the X a structure is characteristic of the Mn 2 CoAl alloy.…”