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

david.peddis@ism.cnr.it– SIF 2015 Magnetic Materials: The dimension is very important permanent micron nanoparticles clusters molecular individual magnets particles clusters spins S = 10 20 10 8 6 5 4 3 2 10 1 magnetic moment multi - domain single - domain david.peddis@ism.cnr.it– SIF 2015

From Multi to mono-domain structure A= Exchange energy density K = Anisotropy energy constant Material dc (nm) Fe 15 Co 35 -Fe2O3 30 SmCo5 750 Kittel_PRB_1946 david.peddis@ism.cnr.it– SIF 2015

CoFe2O4 Nanoparticles (TEM image) C. Cannas, D. Peddis et al Chem Mater. 2010 david.peddis@ism.cnr.it– SIF 2015

Biomedical Applications ( MRI, drug delivery) Supermagnetism Strong interactions Eint>>Ea Collective magnetic state Weak interactions Ea(tot) = Ea +Eint Eint<<Ea Modified SP Superferromagnetism (SFM) Super spin glass (SSG) Interparticle interaction energy (Eint) Biomedical Applications ( MRI, drug delivery) david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Introduction david.peddis@ism.cnr.it– SIF 2015

D. Peddis et al Chem Mater 2013 Introduction Frustration Randomness SuperSpin Glass Spin Glass S. Nakameae, Thesis T<Tg D. Peddis et al Chem Mater 2013 david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 SG/SSG david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 MnFe2O4 david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Structural characterization Oil Water NsDABS SEM <D> XRD (nm) 2 Surface Area (m2/g) 278 TEM <D> BET (nm) 4 david.peddis@ism.cnr.it– SIF 2015

Interparticle Interactions Id (DCD remanent magnetization after saturation) Ir ( IRM remanent magnetization after demagnetization) M Plot M < demagnetizing interaction M = 0, no interaction M > magnetizing interaction david.peddis@ism.cnr.it– ICSM 2014

david.peddis@ism.cnr.it– SIF 2015 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

Measurement done in Uppsala D. Peddis, D. Fiorani, et al. in prep MnFe2O4 SuperSpinglass 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) D. Peddis, D. Fiorani, et al. in prep david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Mössbauer Spectroscopy TBM (K) Mössbauer 62 m (s) 510-9 TmaxZFC(K) SQUID 45 m (s) 10 - 100 david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015

D. Peddis, D. Fiorani, et al. in prep MnFe2O4 SuperSpinglass Power law 0 1.910-12 Tg 45.3 (3) α 8.6 (2) SG systems david.peddis@ism.cnr.it– SIF 2015 D. Peddis, D. Fiorani, et al. in prep

T>Glassy Temperature SG/SSG: Non equilibrium dynamic (NED) T>Glassy Temperature T =T’(<Tg; dT/dt0) T =T’ (<Tg dT/dt0) david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Aging Measurements (ZFC) H = 0 H =10 Oe 150 K 5 K H = 10 Oe 5 K 60 K ZFC reference curve H = 0 H =10 Oe 150 K 20 K tw= 3 h 5 K H = 10 Oe 5 K 60 K ZFC memory curve david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Aging Measurements (TRM) H = 10 H =0Oe 150 K 5 K H = 0 5 K 60 K TRM reference curve H = 10 H =0 Oe 150 K 20 K tw= 3 h 5 K H = 0 Oe 5 K 60 K TRM memory curve david.peddis@ism.cnr.it– SIF 2015

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 MnFe2O4 nanoparticles + Albumin Aqueous dispersion of the ferrite and albumin david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 MnFe2O4 FM NPs@Matrix david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Samples FM Nps AFM Matrix Substrate PEEK 25 μm Buffer Layer Ag 150-160 Ǻ Film ------ 2000 Ǻ Capping Layer 200-250 Ǻ FM NPs Diamag. matrix C. Binns (Leicester, UK) Cluster source MBE source david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Co@Mn; Co@Ag Co Nps Mn Matrix Substrate PEEK 25 μm Buffer Layer Ag 150-160 Ǻ Film ------ 2000 Ǻ Capping Layer 200-250 Ǻ Co NPs Ag matrix Log-normal distribution of particle size (measured in situ by a quadrupole filter) C. Binns (Leicester, UK) 1.8 nm 280 atoms david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Exchange bias effect ZFC FC Co/CoO TN < T < TC T < TN H david.peddis@ism.cnr.it– SIF 2015

Devices governed by Interface Exchange Coupling HARD DISK Magnetoresistive read heads MRAMs Spin valve structure david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– ICSM 2014 Co@Mn; Co@Ag Co Nps Mn Matrix Substrate PEEK 25 μm Buffer Layer Ag 150-160 Ǻ Film ------ 2000 Ǻ Capping Layer 200-250 Ǻ Co NPs Ag matrix Log-normal distribution of particle size (measured in situ by a quadrupole filter) C. Binns (Leicester, UK) 1.8 nm 280 atoms david.peddis@ism.cnr.it– ICSM 2014

david.peddis@ism.cnr.it– SIF 2015 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

david.peddis@ism.cnr.it– SIF 2015 AC Measurements Co@Ag (n = 0.3 – 30 Hz) Co@Mn (n = 0.3 – 30 Hz) Co@Ag Arrhenius law t = t0exp(KaV/KbT) t0 = 6x10-11s Ka=2x107erg/cm3 Co@Mn Power law t = t0 [Tg/(Tmax(n)) – Tg)]a a = 8.2; Tg = 62 K; t0 = 10-9 s In SG 7 < a < 9 david.peddis@ism.cnr.it– SIF 2015

Non-Equilibrium dynamic (NED) H = 0 H =100 Oe 150 K 5 K H = 100 Oe 5 K 80 K ZFC reference curve H = 0 H =100 Oe 150 K 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

M. Vasilakaki, K.N. Trohidou, D. Peddis, et al , PRB 2013 NED: MonteCarlo 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

M. Vasilakaki, K.N. Trohidou, D. Peddis, et al , PRB 2013 NED: Role of exchange Bias M. Vasilakaki, K.N. Trohidou, D. Peddis, et al , PRB 2013 david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Exchange Bias and SSG 30 K david.peddis@ism.cnr.it– SIF 2015

Summary MnFe2O4 Co@Mn (VVF 4.7%) Dynamical properties in a wide range of frequencies Principle of superposition (NED) Role of IEC in NED SSG and EB david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 D. Fiorani. E. Agostinelli, CNR, Rome, Italy A.M.Testa, G. Varvaro, S. Laureti, E. Patrizi, N. Domingo CNR* –Spain C. Binns, S. Baker Univ. of Leicester, UK J. Blackmann Univ. of Reading, UK P. Trohidou, M. Vasalikaki Demokritos, Athens, Greece P. Nordblad, R. Mathieu, M. Hudl Uppsala University david.peddis@ism.cnr.it– SIF 2015

M. Vasilakaki, K.N. Trohidou Monte Carlo Simulation M. Vasilakaki, K.N. Trohidou david.peddis@ism.cnr.it– SIF 2015

david.peddis@ism.cnr.it– SIF 2015 Monte Carlo david.peddis@ism.cnr.it– SIF 2015