Nonequilibrium dynamics in superspin glass systems D Peddis
Non-equilibrium dynamics in superspin glass systems D. Peddis and D. Fiorani E-mail: david. peddis@ism. cnr. it Institute of Matter of Structure (ISM) National Research Council (CNR) Roma - Italy david. peddis@ism. cnr. it– SIF 2015
Magnetic Materials: The dimension is very important permanent magnets S = 10 nanoparticles micron particles 20 10 10 10 multi - domain david. peddis@ism. cnr. it– SIF 2015 8 10 6 10 clusters 5 single - domain 10 4 molecular individual spins clusters 10 3 10 2 10 magnetic moment 1
From Multi to mono-domain structure A= Exchange energy density K = Anisotropy energy constant Kittel_PRB_1946 david. peddis@ism. cnr. it– SIF 2015 Material dc (nm) Fe 15 Co 35 -Fe 2 O 3 30 Sm. Co 5 750
Co. Fe 2 O 4 Nanoparticles (TEM image) david. peddis@ism. cnr. it– SIF 2015 C. Cannas, D. Peddis et al Chem Mater. 2010
Supermagnetism Weak interactions Ea(tot) = Ea +Eint<<Ea Modified SP Strong interactions Eint>>Ea Collective magnetic state Super spin glass (SSG) Superferromagnetism (SFM) Interparticle interaction energy (Eint) Biomedical Applications ( MRI, drug delivery) david. peddis@ism. cnr. it– SIF 2015
Introduction david. peddis@ism. cnr. it– SIF 2015
Introduction Frustration Randomness Spin Glass Super. Spin Glass S. Nakameae, Thesis T<Tg david. peddis@ism. cnr. it– SIF 2015 D. Peddis et al Chem Mater 2013
SG/SSG david. peddis@ism. cnr. it– SIF 2015
Mn. Fe 2 O 4 david. peddis@ism. cnr. it– SIF 2015
Structural characterization Oil Water Ns. DABS SEM TEM david. peddis@ism. cnr. it– SIF 2015 <D> XRD (nm) 2 Surface Area (m 2/g) 278 <D> BET (nm) 4
M Vs. T : ZFC FC Tmax _ZFC (K) 45. 3 (3) Tmax _FC (K) 43. 1 (3) Tirr (K) 50. 0 (2) Tirr/Tmax _ZFC 1. 1 david. peddis@ism. cnr. it– SIF 2015
Mn. Fe 2 O 4 Super. Spinglass Power law 0 4. 2 10 -13 Tg 45. 3 (3) α 8. 6 (2) SG systems Measurement done in Uppsala (P. Nordblad. R Mathieu) david. peddis@ism. cnr. it– SIF 2015 D. Peddis, D. Fiorani, et al. in prep
Mössbauer Spectroscopy Mössbauer SQUID david. peddis@ism. cnr. it– SIF 2015 TBM (K) m (s) 62 5 10 -9 Tmax. ZFC(K) m (s) 45 10 - 100
david. peddis@ism. cnr. it– SIF 2015
Mn. Fe 2 O 4 Super. Spinglass Power law david. peddis@ism. cnr. it– SIF 2015 0 1. 9 10 -12 Tg 45. 3 (3) α 8. 6 (2) SG systems D. Peddis, D. Fiorani, et al. in prep
SG/SSG: Non equilibrium dynamic (NED) T>Glassy Temperature david. peddis@ism. cnr. it– SIF 2015 T =T’(<Tg; d. T/dt 0) T =T’ (<Tg d. T/dt 0)
Aging Measurements (ZFC) H=0 150 K H =10 Oe H = 10 Oe 5 K 5 K 60 K ZFC reference curve H=0 150 K H =10 Oe 20 K tw= 3 h 5 K H = 10 Oe ZFC memory curve david. peddis@ism. cnr. it– SIF 2015 5 K 60 K
Aging Measurements (TRM) H = 10 150 K H =0 Oe H=0 5 K 5 K 60 K TRM reference curve H = 10 150 K H =0 Oe 20 K tw= 3 h 5 K H = 0 Oe TRM memory curve david. peddis@ism. cnr. it– SIF 2015 5 K 60 K
Principle of Superposition First evidence of principle of superposition for superspin glass SG systems R. Mathieu, PRB, 2001 david. peddis@ism. cnr. it– SIF 2015
M. Bellusci, et al , Polymer Intern, 2009 + Mn. Fe 2 O 4 nanoparticles Albumin david. peddis@ism. cnr. it– SIF 2015 Aqueous dispersion of the ferrite and albumin
Mn. Fe 2 O 4 FM NPs@Matrix david. peddis@ism. cnr. it– SIF 2015
Samples FM Nps Substrate PEEK 25 μm Buffer Layer Ag 150 -160 Ǻ Film ------ 2000 Ǻ Capping Layer Ag 200 -250 Ǻ AFM Matrix FM NPs Diamag. matrix C. Binns (Leicester, UK) Cluster source MBE source david. peddis@ism. cnr. it– SIF 2015
Co@Mn; Co@Ag Co Nps Substrate PEEK 25 μm Buffer Layer Ag 150 -160 Ǻ Film ------ 2000 Ǻ Capping Layer Ag 200 -250 Ǻ Mn Matrix Co NPs Ag matrix Log-normal distribution of particle size (measured in situ by a quadrupole filter) C. Binns (Leicester, UK) 1. 8 nm david. peddis@ism. cnr. it– SIF 2015 280 atoms
Exchange bias effect ZFC FC Co/Co. O TN < T C H T < TN david. peddis@ism. cnr. it– SIF 2015
Devices governed by Interface Exchange Coupling HARD DISK MRAMs Magnetoresistive read heads Spin valve structure david. peddis@ism. cnr. it– SIF 2015
Co@Mn; Co@Ag Co Nps Substrate PEEK 25 μm Buffer Layer Ag 150 -160 Ǻ Film ------ 2000 Ǻ Capping Layer Ag 200 -250 Ǻ Mn Matrix Co NPs Ag matrix Log-normal distribution of particle size (measured in situ by a quadrupole filter) C. Binns (Leicester, UK) 1. 8 nm david. peddis@ism. cnr. it– ICSM 2014 280 atoms
ZFC FC Measurements H = 100 Oe Co@Ag: assembly of non interacting particles Superparamagnetic behaviour: Tmax 17 K Curie-law behaviour of c (FC) Tirr/Tmax = 4. 7 Co@Mn: spin-glass like behaviour Tmax of c(ZFC): 65 K Plateau of c(FC) below 30 K Tirr/Tmax = 1. 2 david. peddis@ism. cnr. it– SIF 2015
Non-Equilibrium dynamic (NED) H =100 Oe H=0 150 K H = 100 Oe 5 K 5 K 80 K ZFC reference curve H=0 150 K H =100 Oe 50 K Tw= X 5 K H = 100 Oe 5 K 80 K ZFC memory curve david. peddis@ism. cnr. it– SIF 2015 D. Peddis et al, JPCS; 2010
NED: Monte. Carlo Simulation M. Vasilakaki, K. N. Trohidou, D. Peddis, et al , PRB 2013 david. peddis@ism. cnr. it– SIF 2015 D. Peddis et al, JPCS; 2010
NED: Interface Exchange coupling Without Dipolar Interaction with Interface exchange coupling without Dipolar Interaction Without Interface exchange coupling M. Vasilakaki, K. N. Trohidou, D. Peddis, et al , PRB 2013 david. peddis@ism. cnr. it– SIF 2015
NED: Role of exchange Bias M. Vasilakaki, K. N. Trohidou, D. Peddis, et al , PRB 2013 david. peddis@ism. cnr. it– SIF 2015
Summary Mn. Fe 2 O 4 Dynamical properties in a wide range of frequencies Co@Mn (VVF 4. 7%) Principle of superposition (NED) Role of IEC in NED SSG and EB david. peddis@ism. cnr. it– SIF 2015
D. Fiorani. E. Agostinelli, A. M. Testa, G. Varvaro, S. Laureti, E. Patrizi, N. Domingo CNR, Rome, Italy CNR* –Spain A. C. Binns, S. Baker Univ. of Leicester, UK J. Blackmann Univ. of Reading, UK P. Trohidou, M. Vasalikaki P. Nordblad, R. Mathieu, M. Hudl david. peddis@ism. cnr. it– SIF 2015 Demokritos, Athens, Greece Uppsala University
Monte Carlo Simulation M. Vasilakaki, K. N. Trohidou david. peddis@ism. cnr. it– SIF 2015
Monte Carlo david. peddis@ism. cnr. it– SIF 2015
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