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Probing Electrostructural Coupling on Magnetoelectric CdCr 2 S 4

Probing Electrostructural Coupling on Magnetoelectric CdCr 2 S 4. Jornadas MAP-fis 2012. 1 IFIMUP and IN- Institute of Nanoscience and Nanotechnology and Department of Physics , University of Porto, Rua do Campo Alegre , 687, 4169-007 Porto, Portugal

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Probing Electrostructural Coupling on Magnetoelectric CdCr 2 S 4

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  1. Probing Electrostructural Coupling on Magnetoelectric CdCr2S4 Jornadas MAP-fis 2012 1IFIMUP and IN- Institute of Nanoscience and Nanotechnology and Department of Physics, University of Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal 2CFNUL – Center NuclearPhysics, University of Lisbon, Av. Prof. Gama Pinto, 2, 1649-003, Lisboa, Portugal 3CICECO and Departament of Physics, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal 4ORNL, P.O. Box 2008, MS6475, OakRidge, Tennessee 37831-6475, USA 5APS - Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA 6ITN - InstitutoTecnológico e Nuclear, EN 10 - Apartado 21, 2686-953 Sacavém, Portugal G.N.P. Oliveira 1,2 A.M. Pereira 1 J Amaral 3 A. M Santos 4 T.M Mendonça1 Y.Ren5 J.G. Correia 6 J.P.Araújo1 A.M.L. Lopes 2

  2. Outline Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary • Outline • Motivation • Structural Details – CdCr2S4 • Results • Structural Characterization • Magnetic Characterization • Local Atomic Probe Characterization • Electric Field Gradient – PAC • Atomic displacements – PDF • Conclusions

  3. Motivation Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary • New solid state systems exhibiting simultaneous (anti) ferroelectric ((A)Fe) and (anti) ferromagnetic ((A)Fm) orders - Multiferroics; • maximization of the (A)Fe-(A)Fm coupling  possibility to manipulate the magnetic degrees of freedom electrically or vice-versa; • Possible applications: new non-volatile memories with magnetic/ electric Read/ Write; • Recently, the search for ferroelectricity in materials with known magnetic properties, have already shown some results, namely in: • Manganites (RMnO3, R=Gd, Tb, Lu, Y, Er …) [1] • Chromites with spinel structure (DCr2X4, D=Cd, Hg, and X= S, Se)[2] • Delafossite structure (ABO2, A=Ag, Cu; B=Al,Ga,Cr,... e X=O)[3] • Heterostructures (SrTiO3/BiFeO3/CoFe) Images taken From: N. A. Hill. Why Are There So Few Magnetic Ferroelectrics? The Journal of Physical Chemistry B, 104(29):6694–6709, 2000. [1] S. Lee et al, Nature 451, 805 - 808 (14 Feb 2008) [2] J. Hemberger et al, Nature 434, 364 - 367 (17 Mar 2005) [3] S. Seki et al, Psysical Review Letters 101, 2008

  4. Motivation Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary • New solid state systems exhibiting simultaneous (anti) ferroelectric ((A)Fe) and (anti) ferromagnetic ((A)Fm) orders - Multiferroics; • maximization of the (A)Fe-(A)Fm coupling  possibility to manipulate the magnetic degrees of freedom electrically or vice-versa; • Possible applications: new non-volatile memories with magnetic/ electric Read/ Write; • Recently, the search for ferroelectricity in materials with known magnetic properties, have already shown some results, namely in: • Manganites (RMnO3, R=Gd, Tb, Lu, Y, Er …) [1] • Chromites with spinel structure (DCr2X4, D=Cd, Hg, and X= S, Se)[2] • Delafossite structure (ABO2, A=Ag, Cu; B=Al,Ga,Cr,... e X=O)[3] • Heterostructures (SrTiO3/BiFeO3/CoFe) Images taken From: N. A. Hill. Why Are There So Few Magnetic Ferroelectrics? The Journal of Physical Chemistry B, 104(29):6694–6709, 2000. [1] S. Lee et al, Nature 451, 805 - 808 (14 Feb 2008) [2] J. Hemberger et al, Nature 434, 364 - 367 (17 Mar 2005) [3] S. Seki et al, Psysical Review Letters 101, 2008

  5. Motivation Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary • New solid state systems exhibiting simultaneous (anti) ferroelectric ((A)Fe) and (anti) ferromagnetic ((A)Fm) orders - Multiferroics; • maximization of the (A)Fe-(A)Fm coupling  possibility to manipulate the magnetic degrees of freedom electrically or vice-versa; • Possible applications: new non-volatile memories with magnetic/ electric Read/ Write; • Recently, the search for ferroelectricity in materials with known magnetic properties, have already shown some results, namely in: • Manganites (RMnO3, R=Gd, Tb, Lu, Y, Er …) [1] • Chromites with spinel structure (DCr2X4, D=Cd, Hg, and X= S, Se)[2] • Delafossite structure (ABO2, A=Ag, Cu; B=Al,Ga,Cr,... e X=O)[3] Images taken From: N. A. Hill. Why Are There So Few Magnetic Ferroelectrics? The Journal of Physical Chemistry B, 104(29):6694–6709, 2000. [1] S. Lee et al, Nature 451, 805 - 808 (14 Feb 2008) [2] J. Hemberger et al, Nature 434, 364 - 367 (17 Mar 2005) [3] S. Seki et al, Psysical Review Letters 101, 2008

  6. Crystal Structure - Spinel Family: ACr2X4, A=Cd, Hg, Co, Fe; e X=S, Se, O - Cubic structure: Fd-3m - Cubic Face Centered packing - ACoordenatedtetrahedrically - BCoordenatedoctahedrically Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary A site Cd2+ B site Cr3+ CdS4 CrS6

  7. Magnetic/Dielectric Measurements Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary Inset : Temperature dependence of -1 measured on heating and with H=103 Oe. Graph :-1 as a function of temperature and with different applied magnetic fields (1-101 Oe). Graph:Temperaturedependenceofcomplexdielectric constant. The CdCr2S4 sample was measured to a frequency of 500 KHz, 1 and 5 MHz. Small increase @ 86K -> above ferroelectric transition Phase Transition Para/ferromagnetic Curie T->TC=86 K Curie-Weiss T ->qp=128 K Relaxor like behavior • Below 116 K • short-range magnetic clusters • H>100 Oe cluster destruition

  8. Magnetic Measurements Theoretical model Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary Inverse magnetic susceptibility resulting from theoretical calculations of the Landau theory of phase transitions, considering linear magnetoelectric coupling. Landau Thermodynamic model Short range magnetic cluster (srmc) in the PM regime Linear correlation between electric and magnetic degrees of freedom

  9. Perturbed Angular Correlation (PAC) Probe implanted at ISOLDE/CERN 111In and 117Ag isotopes Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary Hyperfine splitting  Source of information Quadrupolar Frequency EFG Asymetry Parameter Similar to: Vzz– EFG Main component h– Asymmetry parameter Bhf– Magnetic hyperfine field • NMR/NQR • MES

  10. Perturbed Angular Correlation (PAC) 2 Local Environments Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary EFG1 --> Q1=72 MHz and 10.1 EFG2--> Q2=0 MHz (Probe @ Cd cubic site) EFG temperature dependence parameters in the CdCr2S4 system, the fraction of each EFG (top), asymmetry parameter (middle) and fundamental frequency (bottom). Representative R(t) functions, correspondent fits and respective Fourier transform.

  11. Perturbed Angular Correlation (PAC) From 119K to 92K: Dynamic Attenuation is observed(l) Slow thermally activated process Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary ActivationEnergy(Ea) DE=0.1 eV Representative R(t) functions, correspondent fits and respective Fourier transform. order-disorder type phase transiction

  12. Pair Distribuition Function (PDF) 10 Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary G (Å-2) 5 0 -5 5 10 15 r (Å) The PDF results at 80 K of the spinel CdCr2S4 structure (blue dots), as a solid red line (fit), with the difference curve (green) offset for clarity. G(r) is the scattering-length weight measure of the apart obtained via Fourier transform of the reduced total scattering structure function.

  13. Pair Distribuition Function (PDF) 10 Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary The temperature dependence lattice parameter (blue dots) as obtained from Rietveld refinement, the red dashed line is a guide to the eye. G (Å-2) 5 0 -5 5 10 15 r (Å) The blue dots are the isotropic ADPs for Cr refined from undistorted model. The dashed-line (pink) represents the expected behavior from the Einstein-Debye model. The PDF results at 80 K of the spinel CdCr2S4 structure (blue dots), as a solid red line (fit), with the difference curve (green) offset for clarity. Amplitude of the Cr local off-centering. rmax< 0.011 Å

  14. Summary Outline Motivation Crystal Structure Macroscopic characterization Local Characterization Summary PDF PAC PAC e’(T) M(T)

  15. Thank You G.N.P. Oliveira Porto, 19 de Dezembro de 2011 Faculdade de Ciências – Universidade do Porto VII Jornadas do IFIMUP/IN

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