Probing Electrostructural Coupling on Magnetoelectric CdCr 2 S 4 1 IFIMUP and IN- Institute of Nanoscience and Nanotechnology and Department of Physics, University of Porto, Rua do Campo Alegre, 687, Porto, Portugal 2 CFNUL – Center Nuclear Physics, University of Lisbon, Av. Prof. Gama Pinto, 2, , Lisboa, Portugal 3 CICECO and Departament of Physics, University of Aveiro, Campus Universitário de Santiago, Aveiro, Portugal 4 ORNL, P.O. Box 2008, MS6475, Oak Ridge, Tennessee , USA 5 APS - Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA 6 ITN - Instituto Tecnológico e Nuclear, EN 10 - Apartado 21, Sacavém, Portugal G.N.P. Oliveira 1,2 A.M. Pereira 1 J Amaral 3 A. M Santos 4 T.M Mendonça 1 Y. Ren 5 J.G. Correia 6 J.P. Araújo 1 A.M.L. Lopes 2 Jornadas MAP-fis 2012

 Outline  Motivation  Structural Details – CdCr 2 S 4  Results  Structural Characterization  Magnetic Characterization  Local Atomic Probe Characterization  Electric Field Gradient – PAC  Atomic displacements – PDF  Conclusions OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary

 New solid state systems exhibiting simultaneous (anti) ferroelectric ((A)Fe) and (anti) ferromagnetic ((A)Fm) orders - Multiferroics; [1] S. Lee et al, Nature 451, (14 Feb 2008) [2] J. Hemberger et al, Nature 434, (17 Mar 2005) [3] S. Seki et al, Psysical Review Letters 101, 2008  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 (DCr 2 X 4, D=Cd, Hg, and X= S, Se) [2] Delafossite structure (ABO 2, A=Ag, Cu; B=Al,Ga,Cr,... e X=O) [3] Heterostructures (SrTiO 3 /BiFeO 3 /CoFe) possibility to manipulate the magnetic degrees of freedom electrically or vice- versa; Images taken From: N. A. Hill. Why Are There So Few Magnetic Ferroelectrics? The Journal of Physical Chemistry B, 104(29):6694–6709,  maximization of the (A)Fe-(A)Fm coupling  3  Possible applications: new non-volatile memories with magnetic/ electric Read/ Write; OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary

 New solid state systems exhibiting simultaneous (anti) ferroelectric ((A)Fe) and (anti) ferromagnetic ((A)Fm) orders - Multiferroics; [1] S. Lee et al, Nature 451, (14 Feb 2008) [2] J. Hemberger et al, Nature 434, (17 Mar 2005) [3] S. Seki et al, Psysical Review Letters 101, 2008 possibility to manipulate the magnetic degrees of freedom electrically or vice- versa; Images taken From: N. A. Hill. Why Are There So Few Magnetic Ferroelectrics? The Journal of Physical Chemistry B, 104(29):6694–6709,  maximization of the (A)Fe-(A)Fm coupling  4  Possible applications: new non-volatile memories with magnetic/ electric Read/ Write; OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary  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 (DCr 2 X 4, D=Cd, Hg, and X= S, Se) [2] Delafossite structure (ABO 2, A=Ag, Cu; B=Al,Ga,Cr,... e X=O) [3] Heterostructures (SrTiO 3 /BiFeO 3 /CoFe)

[1] S. Lee et al, Nature 451, (14 Feb 2008) [2] J. Hemberger et al, Nature 434, (17 Mar 2005) [3] S. Seki et al, Psysical Review Letters 101, 2008  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] Manganites (RMnO3, R=Gd, Tb, Lu, Y, Er …) [1] Chromites with spinel structure (DCr 2 X 4, D=Cd, Hg, and X= S, Se) [2] Chromites with spinel structure (DCr 2 X 4, D=Cd, Hg, and X= S, Se) [2] Delafossite structure (ABO 2, A=Ag, Cu; B=Al,Ga,Cr,... e X=O) [3] Delafossite structure (ABO 2, 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, OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary  New solid state systems exhibiting simultaneous (anti) ferroelectric ((A)Fe) and (anti) ferromagnetic ((A)Fm) orders - Multiferroics; possibility to manipulate the magnetic degrees of freedom electrically or vice- versa;  maximization of the (A)Fe-(A)Fm coupling   Possible applications: new non-volatile memories with magnetic/ electric Read/ Write;

CrS 6 CdS 4 A site Cd 2+ B site Cr 3+ OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary

Below  116 K   short-range magnetic clusters  H>100 Oe cluster destruition Inset : 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). Small 86K -> above ferroelectric transition Graph: Temperature dependence of complex dielectric constant. The CdCr 2 S 4 sample was measured to a frequency of 500 KHz, 1 and 5 MHz. Relaxor like behavior OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary

8 Short range magnetic cluster (srmc) in the PM regime Linear correlation between electric and magnetic degrees of freedom Theoretical model Landau Thermodynamic model OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary Inverse magnetic susceptibility resulting from theoretical calculations of the Landau theory of phase transitions, considering linear magnetoelectric coupling.

V zz V zz – EFG Main component   – Asymmetry parameter B hf B hf – Magnetic hyperfine field V zz V zz – EFG Main component   – Asymmetry parameter B hf B hf – Magnetic hyperfine field CdCr 2 S In→ 111 Cd Cr/Cd Site 117 Cd→ 117 In Cd Site S IMILAR TO : NMR/NQRMES OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary

10 EFG 1 EFG 1 -->  Q 1 =72 MHz and  1  0.1 EFG 2 EFG 2 -->  Q 2 =0 MHz (P Cd CUBIC SITE ) Representative R(t) functions, correspondent fits and respective Fourier transform. EFG temperature dependence parameters in the CdCr 2 S 4 system, the fraction of each EFG (top), asymmetry parameter (middle) and fundamental frequency (bottom). OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary

F ROM 119K TO  92K: Dynamic Attenuation is observed  Dynamic Attenuation is observed  S LOW THERMALLY ACTIVATED PROCESS   E=0.1 eV A CTIVATION E NERGY (E a ) Representative R(t) functions, correspondent fits and respective Fourier transform. OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary order-disorder type phase transiction

r (Å) G (Å -2 ) The PDF results at 80 K of the spinel CdCr 2 S 4 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. OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary

r (Å) G (Å -2 ) The PDF results at 80 K of the spinel CdCr 2 S 4 structure (blue dots), as a solid red line (fit), with the difference curve (green) offset for clarity. Amplitude of the Cr local off-centering. The temperature dependence lattice parameter (blue dots) as obtained from Rietveld refinement, the red dashed line is a guide to the eye. 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. OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary  r max < Å

OutlineMotivation Crystal Structure MacroscopiccharacterizationLocalCharacterizationSummary understanding of anomalous behavior as recently observed above TC Cr 3+ - Cr 3+ magnetic correlations polar nanoclusters Cr 3+ dynamic off-centering M(T) PAC PDF PAC  ’(T)

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