Materials Science and Nanotechnology

Magnetism of impurities in 3D topological semimetal α-Cd3As2

International Conference on Magnetism and Magnetic Materials
October 09-10, 2017 London, UK

Yu V Goryunov and A N Nateprov

E K Zavoisky Kazan Physical-Technical Institute of the RAS, Russia Institute of Applied Physics, Academy of Science of Moldova, Republic of Moldova

Posters & Accepted Abstracts : Materials Science and Nanotechnology

Abstract:

The electron spin resonance (ESR) for Eu2+, magnetic and conductive properties of the 3D Dirac topological semimetal α-Сd3As2 doped with a small amount of europium impurity was first studied. At present, it has been established that α-Cd3As2 is a topological semimetal, a 3D analog of graphene. The conduction band and the valence band of the α-Cd3As2 have linear dispersion law and touch each other in the 3D Brillouin zone in Dirac nodes. In the presence of time reversibility and inversion symmetry, the Dirac nodes are twice degenerate. The break of any symmetry leads to the splitting of the Dirac node into two Weyl nodes, separated either by the energy interval (see the right insert in the figure) or separated in momentum space. Thus, the presence of a magnetic field or magnetic impurities in the Dirac semimetal (DSM) transforms it into a Weyl semimetal (WSM) and leads to a number of unusual phenomena. Here we assume that we have discovered an unusual type of diamagnetically ordering of magnetic impurity. Data on the magnetic susceptibility (see figure) and ESR showed the presence of an Eu2+ ions additional phase magnetized oppositely to the external field and ordered at TAFM ~ 124 K. Measurements of ESR, carried out at high temperatures, allow us to conclude that this phase (g- factor is near 4.4) consists of the Eu2+ ions located in interstices positions - tetrahedral vacancies in fluorite type cell (see left insert in figure). Whereas the main phase (g ~ 2.2) consists of the Eu2+ ions in the positions substitution of the Cd2+ ions. These positions differ in the degree of chemical compression of the Eu2+ ions. Due to the proximity of the size of the Cd2+ ion to the size of the nonmagnetic Eu3+ ion, this leads to the fact that the magnetic moment of ions in the interstitial positions effectively decreases. About 10% of all Eu2+ ions places in this position. When doping in an amount of about 0.1 at. %Eu, the electron concentration increases from ne = 6•1017 см-3 for α-Сd3As2 to ne = 2,2•1019 см-3 for the doped sample and is temperature independent. The last value is more the Eu impurity content and this requires accurate consideration of question about distribution of the Eu between valence and conduction zones. The ESR data show anomalous large values of the g - factor of the Eu2+ ions, which in its turn indicates very large values of the g factor of the conduction electrons (g ~ 16-18). This indicates very interest interplay between Eu2+, Eu3+ ions and their “free” electrons. We believe that selectively ordering of the Eu2+ ions located in tetrahedral vacancies oppositely to the external field is the result of the splitting of twice degenerate Dirac nodes on two Weyl nodes with different energies, on a similarity to splitting of electronic states with different spin directions.

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