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Mater Sci Nanotechnol 2017
Volume 1 Issue 3
Magnetic Materials 2017
Page 80
October 09-10, 2017 London, UK
International Conference on
Magnetism of impurities in 3D topological
semimetal α-Cd
3
As
2
Yu V Goryunov
1
and
A N Nateprov
2
1
E K Zavoisky Kazan Physical-Technical Institute of the RAS, Russia
2
Institute of Applied Physics, Academy of Science of Moldova, Republic of
Moldova
T
he electron spin resonance (ESR) for Eu
2+
, magnetic
and conductive properties of the 3D Dirac topological
semimetal α-Сd
3
As
2
doped with a small amount of europium
impurity was first studied. At present, it has been established
that α-Cd
3
As
2
is a topological semimetal, a 3D analog of
graphene. The conduction band and the valence band of the
α-Cd
3
As
2
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 Eu
2+
ions
additional phase magnetized oppositely to the external field
and ordered at T
AFM
~ 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 Eu
2+
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 Eu
2+
ions in the positions substitution of
the Cd
2+
ions. These positions differ in the degree of chemical
compression of the Eu
2+
ions. Due to the proximity of the
size of the Cd
2+
ion to the size of the nonmagnetic Eu
3+
ion,
this leads to the fact that the magnetic moment of ions in the
interstitial positions effectively decreases. About 10% of all
Eu
2+
ions places in this position. When doping in an amount
of about 0.1 at. %Eu, the electron concentration increases
from ne = 6•10
17
см
-3
for α-Сd
3
As
2
to ne = 2,2•10
19
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 Eu
2+
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 Eu
2+
, Eu
3+
ions and their “free” electrons.
We believe that selectively ordering of the Eu
2+
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.
gorjunov@kfti.knc.ruMaterials Science and Nanotechnology