Karine Chesnel BYU. Idaho State University, Physics department 22 September 2014

Transcription

1 Karine Chesnel BYU Idaho State University, Physics department 22 September 2014

2 Potential applications of magnetic nanoparticles Magnetic recording Biomedical applications J. Mater. Chem., 19, (2009) - Multifunctionality - Drug transport & delivery - Long-circulation in bloodstream - Hyperthermia - Detectability with MRI

3 Probing the magnetism in Fe 3 O 4 nanoparticles Fe 3 O 4 nanoparticles 5 nm 50 nm size Magnetic configuration of the nanoparticles? Blocking temperature Blocked Superparamagnetic Magnetometry measurements T Ferrimagnetic MACROSPIN X-ray Magnetic scattering / spectroscopy - Orbital and spin moment in Fe 3 O 4 - Magnetic order in nanoparticle assemblies - Dependence with field and temperature - Magnetic fluctuation dynamics

4 Part I Fe 3 O 4 nanoparticles preparation

5 Fe 3 O 4 nanoparticle preparation Inorganic Salt Method (A) FeCl 2 FeCl 3 ABC Mixing the salts Obtaining a paste Addition of water Chemical reaction after several minutes

6 Fe 3 O 4 nanoparticle preparation Inorganic Salt Method (A) Dried samples Drying at 100ºC Filtering Final product: Fe 3 O 4 Cooked at 550ºC for 3.5hrs Placed in vacuum oven

7 Fe 3 O 4 nanoparticle preparation Inorganic Solution Method (B) Final product filtered Mix solutions Mix the Solutions in a 1.75(FeCl 3 ) : 1 (FeCl 2 ) ratio Adjust the ph to 10 Treat it with boiling water Filter with 2L of distilled water

8 Organic method C (thermal decomposition of Fe precursor) (a) Oleate Precursor preparation: Fe(III) acetylacetonate with hexadecane, phenylether, oleic acid, and oleylamine (b) Stir and heat up to 200 C under nitrogen (c) Refluxes at around 250 C (d) Cool down Add ethanol Precipitate by centrifugation Decanter off liquid

9 Part II Bulk structural & magnetic characterizations

10 X-ray Diffraction (XRD) - Spinel Fe 3 O 4 structure - crystallite size: Scherrer formula d = Kλ B cosθ Peak width wavelength Scattering angle Particle Method A B C Particle Size nm 5-15 nm ~ 5 nm

11 Sample A Sample A VSM Magnetization loops Sample B Hysteresis ~200 Oe Hysteresis ~50 Oe Sample C smooth loops amount of hysteresis depends on particle sizes No significant hysteresis

12 Field Cooling (FC) vs. Zero Field Cooling (ZFC) Sample A Large plateau: Large particle Size distributions Sample B Flat plateau Indicating a spread in particle sizes 1000 Oe Sample C 1000 Oe 1000 Oe Sample C after washing

13 Focusing on smaller particles Organic solution method NP16 NP17 NP18

14 X-ray Diffraction Identified spinel structure characteristic of magnetite Fe3O4 Crystallite size: Scherrer formula d Kλ = B cosθ Peak width wavelength Scattering angle Sample Name Average size (nm) XRD Average size (nm) TEM Analysis NP ± ±0.7 NP ± ± 2.5 NP ± ± 1.7 NP ± ± 1.0

15 Magnetization loop - Hysteresis Temperature dependence Particles size 8 nm Size dependence Temperature 400 K 5 nm 8 nm 11 nm Hysteresis increased at lower T (frozen) and saturation field decreased No visible hysteresis for 5nm particles Some hysteresis for 8-11 nm particles

16 Field Cooling behavior (FC/ ZFC) Particles size 8 nm Larger T max at lower cooling field values T = T join - T max > 0 (dipolar couplings) Chesnel et al. Journal of Physics, 521, (2014)

17 Field Cooling behavior (FC/ ZFC) Moment (emu) 5 nm 100 Oe Particle size T max T 5.5 nm 28 K ~10K 8.5 nm 130K ~ 100K 11.0 nm 170K ~ 50K Moment (emu) 8 nm Big variations with particle size Blocking T increases from 28K to 170K when size doubles Variable amounts of dipolar couplings between particles Moment (emu) 11 nm Chesnel et al. Journal of Physics, 521, (2014) Temperature (K)

18 Fe 3 O 4 nanoparticles Self-assembling Regions of different orientations Attempts for vast uniform layers Particles tend to self assemble in a compact hexagonal lattice

19 Fe 3 O 4 nanoparticles layers / Si 3 N 4 membranes: Self-assembling Thinning the layer by decreasing the concentration adjusting the concentration to achieve a uniform monolayer Low concentration (TEM mesh) Intermediate concentration TEM images

20 Part III Synchrotron measurements

21 Magnetic Scattering endstation at SSRL, Stanford CCD detector Cryogenic Sample holder X-rays Vaccum chamber

22 Setup for X-ray Magnetic Circular dichroism (XMCD)

23 X-ray Magnetic Circular Dichroism (XMCD) results Transmission T I = I 0 I H I 0 Absorption A ln I = I0 Absorption (normalized to white line) at Fe L 3 edge H+ H - Measured in positive and negative helicities or positive and negative fields XMCD E 2 XMCD A A XMCD = A + A eV E 1 E 3 720eV energy (ev)

24 XMCD results on Fe 3 O 4 nanoparticles Orbital Moment Sum rules: Spin Moment Orbital moment M L quenched Spin moment M S reduced / bulk

25 XMCD results on Fe 3 O 4 nanoparticles Measured M L and M S for different particle sizes at different temperatures Total moment M = M L + M S Nanopart. size (nm) 300 K 80K 11.3 ± ± ± Cai, Chesnel et al. Journal of Applied Physics, 115, 17B537 (2014)

26 Coherent X-ray magnetic scattering X-ray beam Pinhole Magnetic film Detector X-ray Energy Tuned to resonant edge (ex Co L 3 edge) Coherent illumination Resonant Scattering Magnetic Speckle pattern Synchrotron Radiation Tool Envelope: Long range magnetic order Speckle: Local morphology

27 X-ray magnetic scattering patterns (first run) Ring: Particles correlation Detector off-centered to left Interparticle distance 5.8nm Diffuse charge scattering Direct beam position

28 Attempting to extract the magnetic signal Total scattering intensity Dichroic ratio Switching helicity or switching field

29 X-ray scattering patterns (Second run) Direct beam position

30 From X-ray scattering patterns to radial profiles 1.40E E E+008 Particles Bragg peak 8.00E Intensity 6.00E E E E Fine set of rings Blocker & shadow corrections center radius (pixels)

31 Extracting magnetic signal from the XRMS profiles Extracting magnetic signal by switching magnetic field Comparing magnetic profiles at different helicities E= 706eV, circular E =706eV, linear

32 Extracting magnetic signal from the XRMS profiles Magnetic profiles outside the L 3 edge 700eV 719eV

33 Extracting magnetic signal from the XRMS profiles Comparing profiles at different energies, at the L 3 edge Positive Negative Zero Positive-Negative Positive-Zero Negative-Zero Jan16 B10 705eV Positive Helicity 0.2 Intensity Q / pixels Positive Negative Zero Positive-Negative Positive-Zero Negative-Zero Jan16 B eV Negative Helicity Intensity Q / pixels 704eV +/- 705eV +/- 706eV +/-

34 Measuring inter-particle distances and correlations with XRMS (third run)

35 Extracting a magnetic signal Dependence with energy Dependence with field direction Evidence of magnetic contribution

36 Magnetic profile: dependence with field Ferro order AF order Probing the magnetic order in the NP assemblies

37 Focusing on Magnetic speckles Magnetic satellite 3D view Spatial intensity fluctuations β = Coherence degree I 2 I I FePd film 2 2 I Measured intensity I Averaged intensity I

38 Speckle patterns cross-correlation metrology Speckle pattern A B Correlation pattern Speckle correlation Background (incoherent Scattering) No correlation Correlation coefficient [ ] ( ) A B 0 < < ρ A, B >= [ A A] [ B B] < 1 Exact same configuration

39 Looking at dynamics of fluctuations Speckle time-correlation Coherent part ~ 0.35%! Speckle correlation pattern

40 Looking at dynamics of fluctuations Speckle time-correlation 0.6 Sample D2 90K 180K, 0 90K, Sample BF Rho K Rho RT, 3A RT,0A 90K,3A 90K, 0A time (sec) time (sec) 45% loss in 5 min at 180K 65% loss in 15 min at 300K

41 Conclusions Successfully fabricated Fe 3 O 4 nanoparticles Characterized superparamagnetic behavior Particles tend to self-assemble in hexagonal lattices XMCD results: measured orbital M L and spin M S XMRS scattering patterns: Magnetic profile: magnetic order differing from charge order First results speckle time- correlations: Successful recording of fluctuations dynamics at slow time scales (min): characteristic time ~ min Future directions Complete analysis at different energies, different polarization different field values and different T Refine correlation analysis and measure relaxation times Study dependency with particle sizes and concentration

42 Thanks Matea Trevino Matthew Rytting Andrew Westover Yanping Cai Benny Wu Tianhan Wang Cat Graves Andreas Scherz Dr. Roger Harrison Betsy Olson Jared Hancock

43 Joe Nelson Andrew Westover William Anderton Young Byun Looking for graduate students! Condensed matter Nanomagnetism X ray scattering Contact: Karine Chesnel kchesnel@byu.edu