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Experimental and theoretical Studies of the Magnetocaloric Effect (MCE) in the Mn 5-x Fe x Si 3 Series PowerPoint Presentation
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Experimental and theoretical Studies of the Magnetocaloric Effect (MCE) in the Mn 5-x Fe x Si 3 Series. Michael Gottschlich 1. Olivier Gourdon 1 , Michael Ohl 1 , Jörg Perßon 2. 1 Jülich Centre for Neutron Science outstation at the SNS at ORNL

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slide1

Experimental and theoretical Studies of the Magnetocaloric Effect (MCE) in the Mn5-xFexSi3 Series

Michael Gottschlich1

Olivier Gourdon1, Michael Ohl1, Jörg Perßon2

1 Jülich Centre for Neutron Science outstation at the SNS at ORNL

2 Peter Grünberg Institut Forschungszentrum Jülich

the mce
The MCE

The MCE is related mostly to the magnetic entropy changes of magnetic materials under the influence of an applied field

  • Tc where the phenomenon occurs
  • DS –MCE obtains
  • DT of the MCE phenomenon

MCE of Gd, Gschneider, et al. 2005

slide7

Unit cell of Mn5-xFexSi3 at room temperature

Hexagonal P63/mcm

Si

Fe(ab)

Fe(c)

a = b ~ 6.8 Å

c ~ 4.7 Å

slide8

Unit cell of Mn5-xFexSi3 at room temperature

Hexagonal P63/mcm

  • low cost
  • non-toxic

Si

Fe(ab)

Fe(c)

a = b ~ 6.8 Å

c ~ 4.7 Å

unit cell of mn 5 x fe x si 3 at room temperature

Unit cell of Mn5-xFexSi3 at room temperature

Hexagonal P63/mcm

  • low cost
  • non-toxic
  • structure flexible/ accommo-date various chemical substitutions
  • understanding how the MCE works

Si

Fe(ab)

Fe(c)

a = b ~ 6.8 Å

c ~ 4.7 Å

synthesis mn 5 x fe x si 3 x 0 1 2 3 4

Synthesis: Mn5-xFexSi3 (x=0,1,2,3,4)

  • polycrystalline samples prepared by inductive crucible free melting
  • structures preliminary confirmed by x-ray diffraction
  • magnetization measurements
  • chemical Analysis
mce in mn 5 x fe x si 3

MCE in Mn5-xFexSi3

MCE of Gd5Ge2Si2 (2T)~27 J/kg K

E. Brück et al. 2007

Songlin et al. 2002

Recently at ORNL (X=4)

slide12

Neutron the rescue…

80000

60000

40000

20000

0

Intensity

0 0.5 1.0

d [Å]

  • to elucidate the coloring problem: Fe vs. Mn on both sites (no discernable by X-ray)
  • to investigate the magnetic ordering

…POWGEN at the SNS

  • TOF instrument (ideal for atomic occupation / high Q)
  • high resolution:Δd/d ~0.1%

Diamond pattern collected on POWGEN

Schematic view of POWGEN

slide13

Mn5-xFexSi3 (x= 0 to 4)

Si

Fe(ab)

Fe(c)

300 K

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

x=2

Normalized Intensity

Normalized Intensity

“unique precision”

0.5 1.0 1.5 2.0 2.5 3.0 3.5

d [Å]

slide14

Mn5-xFexSi3 (x= 0 to 4)

300 K

Candini et al. 2004

Our data from SNS

Very similar results.

magnetization measurements

Magnetization Measurements

best MCE candidate

slide17

LT structure of Mn5-xFexSi3 x=4

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

Normalized Intensity

300K

0.5 1.0 1.5 2.0 2.5 3.0 3.5

d [Å]

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

Normalized Intensity

10K

0.5 1.0 1.5 2.0 2.5 3.0 3.5

d [Å]

P63/mc‘m‘

Si

Fe(ab)

Fe(c)

Moments II c-axis for x=4 in the ferromagnetic phase

dft calculations

DFT Calculations

using program „TB-LMTO-ASA“, R. Tank et al.

=> occupations of Mn vs. Fe

=> stability of the AF and F phases

From group to sub-group

X=4

Si

1Mn for 4Fe

Name wyck x y z

___________________

M1 2i 0.3333 0.6667 0.0000

M2 2i 0.6667 0.3333 0.5000

M3 2i 0.7636 0.7636 0.2500

M4 2i 0.2364 0.0000 0.2500

M5 2i 0.0000 0.2364 0.2500

Si1 2i 0.4043 0.4043 0.2500

Si2 2i 0.5957 0.0000 0.2500

Si3 2i 0.0000 0.5957 0.2500

Fe(ab)

Fe(c)

P63/mcm

P-1

Model 1

Mn on Fe(c)

Model 2

Mn on Fe(ab)

dft calculations19

DFT Calculations

LDA and LSDA calculations have been performed both confirmed that:

Model 1

Mn on Fe(c)

Model 2

Mn on Fe(ab)

is less stable than

by 0.5 eV/unit cell

in agreement with the refined data

  • magnetic moments of ~1.7 mB
  • small magnetization on Si ~0.1 mB (indirect effect)

Total Density of States

slide20

Mn5-xFexSi3 x=0

Negative MCE occurs here

slide22

Mn5-xFexSi3 x=0

AF2 structure

orthorhombic

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

85 K

Normalized Intensity

0.5 1.0 1.5 2.0 2.5 3.0 3.5

d [Å]

slide23

Mn5-xFexSi3 x=0

AF1 structure

monoclinic

60 K

Normalized Intensity

d [Å]

slide24

Acknowledgements

POWGEN at SNS ORNL

  • Jason Hodges
  • Ashfia Huq
  • HB2a at HFIR ORNL
  • Ovidiu Garlea
  • Clarina Dela Cruz
  • JANA Software
  • Vaclav Petricek
slide25

Summary and future direction

  • the combination of experimental data and theoretical tools lead to a better understanding of the MCE property.
  • chemical substitutions
  • single crystals for further neutron scattering experiments

Thank you very much for your attention!