The first principle calculation study on half-metallic spinel

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The first principle calculation study on
half-metallic spinel
Presenter Min Feng Advisor Professor Xu
Zuo College of Information Technical Science,
Nankai University, Tianjin, China
Spinel An important class of ceramic compounds
with a variety of interesting properties. The
earliest suggestion of half metallic character
was from a calculation of the spinel structure
magnet CuCr2S4.
Half-metallicity an intrinsic materials property
of an energy gap between valence and conduction
bands for electrons of one spin polarization and
continuous bands for the electrons of the other
spin polarization.
(100) direction
Discovered by de Groot and Mueller band
structure of NiMnSb for (a) the majority-spin
direction and (b) the minority-spin direction.
Physical Review Letters 50(25) 2024
Structure can be fully described by lattice
constant (a) and oxygen parameter (u).
Tetrahedral coordination site ( A site)
Octahedral coordination site ( B site)
X atoms in a nearly fcc close-packed arrays
Chemical formula AB2X4
Space group O7h (Fd3m).
We use GGA (generalized gradient approximation)
U method to investigate the electronic structure
and magnetic properties of spinel. The
calculation is accomplished by using the VASP
code and the WIEN2K code. The additional on-site
Coulomb repulsion (U) is applied to the d orbits
of the transition metal cations.
Applications components for MR devices, spin
tunneling devices, etc. in field of spintronics.
free direction
No smoking gun experiment to prove or disprove
half-metallicity. Electronic structure
calculations continue to play an important role
in the search for new half-metallic materials.
My research work
CuFe2O4
LiCr2O4
The optimized structure of inverse copper ferrite
is tetragonal, with ab8.136Å, c8.669Å. Thus
c/a ratio is 1.065, due to the Jahn-Teller
distortion of Cu2 ions. The optimized structure
of normal spinel copper ferrite is cubic, with
abc8.062 Å.
Structure optimized using VASP with a 121212
k-mesh. The breaking conditions for the
electronic and ionic loops are 10-4 and 10-3 eV .
The electronic structure and magnetic properties
calculation is accomplished by using the WIEN2K
code with a 212121 k-mesh.
The optimized structure parameters are a 8.260Å
and u 0.388. The dependency of DOS on U in
LiCr2O4 implies that the half-metallicity may be
robust to U. While half-metallicity can hardly
exist in CuCr2S4.
Calculated density of states (DOS) of copper
ferrite with U4eV. From (a) to (e), the factor
of inverse degree x0, 0.25, 0.5, 0.75, 1,
respectively. The partially inverse structures
are labeled by their Cu concentration in B sites
and name of space group, for example, 0.25B CM
means the structure has 25 Cu ions in B sites,
and its space group is CM (8).
We also calculated the local magnetic moment of
Cr and the interstitial magnetic moment in
LiCr2O4, and their dependencies on U are shown on
the left. When U increases, mCr increases and
mint decreases due to the increasing trend of
localization.
When x0, 0.25, 0.5, the copper ferrite systems
are half-metallic.
The copper ferrite system with 75 Cu ions in B
site is metallic. And the inverse spinel copper
ferrite, in which x1, is semi-conducting.