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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

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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