Prasenjit Roy, Gilles A. de Wijs, Robert A. de Groot Electronic Structure of Material, Radboud University Nijmegen 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 T c . They are called weak magnets. Viz: ZrZn 2 and TiBe 2 . Recently, MnFeSiP series of materials were discovered, with very high efficiency of MCE near room temperature and stability of structure with doping. CalculaDons 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 GGAPBE funcJonal. For MnFeSiP the space group number is 189 and the unitcell is hexagonal. The density of states for MnFeSiP shows that Mn at the 3g posiJon serves as a strong magnet which conserve its moment at Curie temperature while 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. | Local moment | Mn Fe Si P FerromagneDc 2.8 1.5 0.1 0.1 AnDferromagneDc 2.8 0.8 0.1 0.1 If we compare the difference electron density of Codoped, Crdoped and Mn rich MnFeSiP based materials; we see: The electron density is moving from Fe to Si, suggesJng a possible covalent bonding. From the picture and the parJal occupaJon of delectrons we can also argue, 3d xy and 3d x2y2 orbitals are responsible in these materials for change in Curie temperature and adiabaJc latent heat. The trend from the periodic table is also visible. 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 Curie temperature and the local moment by means of different chemical composiJon and structures. References 1. Anders Smith, Chris1an R.H. Bahl, Rasmus Bjork, Kurt Engelbrecht, Kasper K Nielson, Nini Pryds, Adv. Energy Material, 2012, 2, 12881318. 2. N.H. Dung, Z. Qu. Ou, L. Caron, L. Zhang, D. T. Cam Thanh, G. A. de Wijs, R. A. de Groot, K. H. J. Buschow, E. Bruck, Adv. Energy Material, 2011, 1, 1215. Strong layer Weak layer Strong layer Weak layer Spin Up Spin Down AnJferromagnet Forces on atoms At Curie Temp. AnJferromagneJc arrangement in z direcJon. FerromagneJc pDOS AnJferromagneJc pDOS 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. 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 Gd 5 Si 2 Ge 2 . Successful implementaJon of GMCE can reduce the world’s energy consumpJon by 8% within 2030 : as proposed by the UN.

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Prasenjit Roy, Gilles A. de Wijs, Robert A. de Groot Electronic Structure of Material, Radboud University Nijmegen

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.

CalculaDons 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.

The density of states for MnFeSiP shows that Mn at the 3g posiJon serves as a strong magnet which conserve its moment at Curie temperature while 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.

| Local moment | Mn Fe Si P

FerromagneDc 2.8 1.5 0.1 0.1

AnDferromagneDc 2.8 0.8 0.1 0.1

If we compare the difference electron density of Co-‐doped, Cr-‐doped and Mn rich MnFeSiP based materials; we see:-‐

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.

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 Curie temperature and the local moment by means of different chemical composiJon and structures.

References 1. Anders Smith, Chris1an R.H. Bahl, Rasmus Bjork, Kurt Engelbrecht, Kasper K Nielson, Nini Pryds, Adv. Energy Material, 2012, 2, 1288-‐1318. 2. N.H. Dung, Z. Qu. Ou, L. Caron, L. Zhang, D. T. Cam Thanh, G. A. de Wijs, R. A. de Groot, K. H. J. Buschow, E. Bruck, Adv. Energy Material, 2011, 1, 1215.

Strong layer

Weak layer

Strong layer

Weak layer

Spin Up

Spin Down

AnJferromagnet

Forces on atoms At Curie Temp.

AnJferromagneJc arrangement in z direcJon.

FerromagneJc p-‐DOS AnJferromagneJc p-‐DOS

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.

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.