Wydarzenia

Seminarium Międzynarodowego Laboratorium Silnych Pól Magnetycznych i Niskich Temperatur PAN

Electrical and galvanomagnetic properties of half-metallic ferromagnetic Heusler alloys

prof. Vyacheslav Marchenkov

Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg, Russia Ural Federal University, Ekaterinburg, Russia

Materials that exhibit half-metallic ferromagnetism (HMF) are potential candidates for application in spintronics. Some of the Heusler alloys were predicted to be in a half-metallic state. The main feature of the electronic structure of HMF is the presence of an energy gap at the Fermi level in one spin sub-band and a metallic character of the density of states in the other. This can lead to 100% spin polarization of the charge carriers, which can be used for spintronic devices. The depth and the width of the energy gap can vary quite strongly in different HMF. This feature of the electron spectrum is usually predicted by ab initio band structure calculations and is experimentally observed by measurements of the optical properties. Due to significant changes in the electronic spectrum it should manifest itself also in other electronic properties at the transition from the ferromagnetic to the paramagnetic state. In particular, we would expect the presence and a manifestation of the "gap" peculiarities in the electronic transport properties. We studied the electroresistivity ρ and the galvanomagnetic properties of Heusler alloys X₂YZ (X = Co, Fe, Ni; Y = Cr, Mn, Fe, Ni, Ti, V; Z = Al, Ga, Si) in the temperature range from 4.2 to 800 K and in magnetic fields of up to 15 T. It was experimentally demonstrated that in contrast to the usual metallic behavior of ρ(T), e.g., in ferromagnetic Ni₂MnGa, an abnormal behavior is observed in high-resistive HMF Heusler alloys, i.e., a negative slope at T <T_C and a minimum of ρ near T_C (T_C is Curie temperature). These anomalies can be explained by a two-current conduction model that takes into account the presence of an energy gap near the Fermi level in the electronic spectrum for electrons with spin down (minority). The results are in a good agreement with calculations of the electronic band structure and can be used for the development of materials and devices for spintronics.