The document discusses the giant magnetocaloric effect (GMCE) observed in materials like MnFeSiP. It summarizes that the GMCE occurs due to a phenomenon called "mixed magnetism", where different elements in the material behave as either strong or weak magnets. First-principles calculations reveal that the GMCE arises from an antiferromagnetic arrangement of the magnetic moments and a transfer of electron density from Fe to Si, involving the 3dxy and 3d x2-y2 orbitals of Fe. Optimizing the chemical composition and structure could enable controlling the Curie temperature and local magnetic moments to realize the GMCE near room temperature.
Personal Resilience in Project Management 2 - TV Edit 1a.pdf
Roy-document-1
1. Prasenjit
Roy,
Gilles
A.
de
Wijs,
Robert
A.
de
Groot
Electronic
Structure
of
Material,
Radboud
University
Nijmegen
IntroducDon
Historically
the
discovery
of
Magnetocaloric
Effect
is
conferred
to
Weiss
and
Piccard
(1918)
for
an
experiment
on
Nickel.
They
proved
that
the
effect
is
reversible
and
most
effecJve
near
the
Curie
temperature.
In
1997
Pecharsky
and
Gschneider
discovered
“Giant
Magnetocaloric
Effect
(GMCE)”
in
Gd5Si2Ge2.
Successful
implementaJon
of
GMCE
can
reduce
the
world’s
energy
consumpJon
by
8%
within
2030
:
as
proposed
by
the
UN.
The
QuesDon
The
Giant
Magnetocaloric
effect
(GMCE)
is
important
for
refrigeraJon.
But
the
mechanism
of
it
sJll
remains
unknown.
First
principle
electronic
structure
calculaJon
elucidates
the
microscopic
origin
of
giant
MCE.
Backgrounds
Most
magnets
realign
the
moments
at
the
Curie
temperature,
and
the
net
moment
becomes
zero.
They
are
called
strong
magnets,
like
Fe,
Ni
etc.
Very
few
magnets
loose
the
local
moments
at
Tc.
They
are
called
weak
magnets.
Viz:
ZrZn2
and
TiBe2.
Recently,
MnFeSiP
series
of
materials
were
discovered,
with
very
high
efficiency
of
MCE
near
room
temperature
and
stability
of
structure
with
doping.
FerromagneJc
p-‐DOS
AnJferromagneJc
p-‐DOS
If
we
compare
the
difference
electron
density
of
Co-‐doped,
Cr-‐doped
and
Mn
rich
MnFeSiP
CalculaDons
based
materials;
we
see:-‐
Most
of
the
calculaJons
were
done
by
using
pseudopotenJal
method
implemented
in
VASP
as
a
primary
tool;
and
WIEN2K,
incorporaJng
LAPW
method
for
more
precise
calculaJon.
In
both
cases
we
used
GGA-‐PBE
funcJonal.
For
MnFeSiP
the
space
group
number
is
189
and
the
unitcell
is
hexagonal.
Spin
Up
Strong
layer
AnJferromagnet
Weak
layer
Spin
Down
Strong
layer
Weak
layer
AnJferromagneJc
arrangement
in
z
direcJon.
The
electron
density
is
moving
from
Fe
to
Si,
suggesJng
a
possible
covalent
bonding.
From
the
picture
and
the
parJal
occupaJon
of
d-‐electrons
we
can
also
argue,
3dxy
and
3d
x2-‐y2
orbitals
are
responsible
in
these
materials
for
change
in
Curie
temperature
and
adiabaJc
latent
heat.
The
trend
from
the
periodic
table
is
also
visible.
Forces
on
atoms
At
Curie
Temp.
OpDmizaDon
Using
the
acquired
knowledge
we
further
extended
our
research.
The
UTX
materials
also
showed
Mixed
MagneJsm.
The
successful
explanaJon
of
the
GMCE
in
near
future
will
represent
an
understanding
of
controlling
the
The
density
of
states
for
MnFeSiP
shows
that
Mn
at
the
3g
posiJon
serves
Curie
temperature
and
the
local
moment
by
means
of
different
chemical
as
a
strong
magnet
which
conserve
its
moment
at
Curie
temperature
while
composiJon
and
structures.
Fe
at
the
3f
plane
looses
half
of
its
moment
(weak
magnet).
This
kind
of
arrangement
is
called
MIXED
MAGNETISM
and
holds
the
key
of
GMCE
at
room
temperature.
References
1.
Anders
Smith,
Chris1an
R.H.
Bahl,
Rasmus
Bjork,
Kurt
Engelbrecht,
Kasper
K
Nielson,
Nini
Pryds,
Adv.
Energy
Material,
2012,
2,
1288-‐1318.
|
Local
moment
| Mn Fe Si P
2.
N.H.
Dung,
Z.
Qu.
Ou,
L.
Caron,
L.
Zhang,
D.
T.
Cam
Thanh,
G.
A.
de
FerromagneDc 2.8 1.5 0.1 0.1 Wijs,
R.
A.
de
Groot,
K.
H.
J.
Buschow,
E.
Bruck,
Adv.
Energy
Material,
2011,
1,
1215.
AnDferromagneDc 2.8 0.8 0.1 0.1