Soft magnetic materials: from microsensors to cancer therapy. Alfredo García-Arribas

Transcription

1 Soft magnetic materials: from microsensors to cancer therapy Alfredo García-Arribas New materials for sensors and actuators. Pamplona, 28 septiembre

2 Outline Introduction Magnetism basics Magnetization process Soft magnetic materials Magnetic microsensors Magnetic field sensors Magneto-impedance sensors Electronic compass Magnetoelastic sensors Magnetoelastic effect Magnetoelastic resonance Oil viscosity sensor Magnetic nanodiscs for cancer therapy Magneto-mechanical actuation Magnetic vortex state Sub-100 nm vortex discs Nanodiscs in cancer cells 2

3 Outline Introduction Magnetism basics Magnetization process Soft magnetic materials Magnetic microsensors Magnetic field sensors Electronic compass Magneto-impedance sensors Magnetoelastic sensors Magnetoelastic effect Magnetoelastic resonance Oil viscosity sensor Magnetic nanodiscs for cancer therapy Magneto-mechanical actuation Magnetic vortex state Sub-100 nm vortex discs Nanodiscs in cancer cells 3

4 Magnetism Basics Magnetism in matter is a quantum effect. Some ingredients are necessary: Spin of the electrons It can have only two orientations: up and down. Atomic magnetic moments Spins sum according to certain rules. Only some atoms display net atomic moment. Exchange interaction Only in few materials these atomic moments aligns themselves spontaneously ferromagnetic antiferromagnetic ferrimagnetic For applications, only ferromagnetism is useful. Ferrimagnetism is similar. 4

5 Magnetism Basics Crystal anisotropy Exchange is isotropic. Magnetic moments align in selected directions according to crystal symmetry. Magnetostatic energy A magnetized material produced a strong external magnetic field. Huge magentostatic energy. Magnetic domains The magnetization is distributed in domains with different orientations, compatible with anisotropy to minimize the magnetostatic energy. The material is macroscopically no-magnetized 5

6 Magnetism Basics Domain walls The boundary between domains are called domain walls Domain walls increase the exchange energy. The equilibrium configuration is an energy compromise. Magnetic force microscopy Kerr effect microscopy 6

7 Magnetization process When a magnetic field is applied, the material is magnetized. Domain wall movement Rotation of the magentization M Hex M is the magnetic moment per unit volume, measured in the direction of the applied field 7

8 Hysteresis loop M Mr Hc Hex Domain walls are pinned in defects, grain boundaries, etc. HARD magnetic material SOFT magnetic material 8

9 Magnetic materials Hard magnetic materials Magnets. large Mr: produce external magnetic field. large Hc: are difficult to demagnetise Soft magnetic materials Large permeability. Low energy loss (slim loop) µ r = dm dh r Have large response to small magnetic fields. Concentrate and guide the magnetic flux. Transformers Electric motors 9

10 Soft magnetic materials The softness of a magnetic material is determined by Intrinsic properties Crystal structure Magnetic anisotropy Permalloy Fe20Ni80 has no crystal anisotropy Treatments Cold working Thermal annealing. Grain-oriented silicon steel for transformers The softness can be induced only in the direction of interest Permalloy deposited under applied field 1.0 easy axis H Kerr signal easy hard H H (Oe) 10

11 Soft magnetic materials Amorphous magnetic alloys (metallic glasses) Topological (and chemical) disorder. No pinning for domains walls. No magnetic anisotropy Extremely soft! Fe, Co, Ni and B, P, C, Nb, Zr, etc Rapid quenching preparation method cooling rates of 10 6 degrees per second crystalline alloy amorphous alloy Prepared in the form of ribbon or wires 11

12 Outline Introduction Magnetism basics Magnetization process Soft magnetic materials Magnetic microsensors Magnetic field sensors Electronic compass Magneto-impedance sensors Magnetoelastic sensors Magnetoelastic effect Magnetoelastic resonance Oil viscosity sensor Magnetic nanodiscs for cancer therapy Magneto-mechanical actuation Magnetic vortex state Sub-100 nm vortex discs Nanodiscs in cancer cells 12

13 Magnetic field sensors The great sensitivity to small fields makes soft magnetic materials excellent for magnetic field sensing. Electronic compass Measure the Earth magnetic field (about 0.5 G or 50 μt). Together with accelerometers and gyroscopes provide attitude detection. Technologies using soft magnetic materials Magneto-inductive detection Micro flux-gate Anisotropic magnetoresistance (AMR) High resolution. Poor microelectronic integration. Difficult integration. Noise problems. Both use the change in permeability ed ons such ncludes our Used in some systems Need of reset field. Honeywell ellation, by 4.0 the Use magnetorresistance s, logy that provides advantag nd linearity, solid-s Earth s 13

14 Magnetic field sensors Hall sensors Winner technology. Use Si Hall effect. Completely integrable (sensor and logic in the same die). Low sensibility. Need a magnetic concentrator. The Permalloy concentrator amplifies the magnetic field and guides the perpendicular components into the planar sensors. 14

15 Magneto-impedance sensors Search for totally integrable solutions with higher sensitivity. Magneto-impedance effect j (A/m 2 ) i ac (!) H Skin effect: the alternating current flows near the surface of the conductor = r 2! µ δ δ: penetration depth r Z Z max μ high ΔZ ΔZ MI (%) = x 100 Z min Z min μ low H 15

16 Magneto-impedance sensors MI in planar samples (i.e. thin films) M Z max Z μ high H Transverse anisotropy H ΔZ max. sensibility μ low Z min Very large sensitivity at low fields in samples with in-plane, transverse anisotropy. Need for thick samples to enhance the skin effect Problem: softness lost in thicker samples H 20 nm thick 260 nm thick H Kerr signal easy hard Kerr signal easy hard H H (Oe) well defined in-plane anisotropy H (Oe) development of out-of-plane anisotropy 16

17 Magneto-impedance sensors First strategy: increase thickness using non-magnetic spacers Py layers below critical thickness thin (6 nm) Ti spacers ~1 μm A. Svalov et al. APL 100, (2012) Magnetic softness preserved MI ratio enhancement M/M s H (Oe) MI (%) f = 200 MHz MI = 23 % H (Oe) 17

18 Magneto-impedance sensors Second strategy: enhance MI using the magneto inductive effect 350 Extraordinary performance! 4 Py/Ti Cu Py/Ti Magnetic Conductive non-magnetic Magnetic Search for best layer configuration: thickness of the layers thickness ratio of magnetic to nonmagnetic layers Best performing multilayer structure is ΔZ/Z (%) s (%/Oe) f = 23 MHz H (Oe) smax = 300%/Oe (2.7 Ω/Oe = 27 kω/t) Z (Ω) dz/dh (Ω/Oe) [Py(100 nm)/ti(6 nm)] 4 / Cu(400 nm) / [Ti(6 nm)/py(100 nm)] 4 18

19 Magneto-impedance sensors Micro-sensors deposited onto Si substrate shaped by photolithography length 0.5#mm 1.0#mm 1.5#mm 2.0#mm width 20#!m microstrip coplanar 40#!m 60#!m Electronic compass Sample θ 80#!m 100#!m 120#!m 140#!m Earth field 16.5 Z (Ω) θ (º) s = 25 mω/º 19

20 Outline Introduction Magnetism basics Magnetization process Soft magnetic materials Magnetic microsensors Magnetic field sensors Electronic compass Magneto-impedance sensors Magnetoelastic sensors Magnetoelastic effect Magnetoelastic resonance Oil viscosity sensor Magnetic nanodiscs for cancer therapy Magneto-mechanical actuation Magnetic vortex state Sub-100 nm vortex discs Nanodiscs in cancer cells 20

21 Magnetoelastic sensors Uses the coupling between magnetic and mechanical properties Magnetostriction Change of length when a magnetic material is magnetized H = 0 H Used for actuation First version of SONAR ~ Magnetostrictive actuators (Terfenol) l l + Δl Magnetoelastic effect Change in the magnetic state when a magnetic material is deformed H = 0 σ > 0 σ = 0 σ σ produces large permeability changes 21

22 Magnetoelastic sensors The magnetoelastic effect can be used to measure deformation, force, torsion, etc. τ torductor ABB The detection is non-contact, using pick-up coils to measure permeability changes. 22

23 Magnetoelastic resonance An alternating field excites magneto-elastic waves in the material. h(t) = h o sen ωt m(t) v(t) At selected frequencies, mechanical resonances builds up. ε, m, v! r = n L s E ω r h(t) = h o sen ωt H o ωr ω Young modulus E = E(H): the resonance can be tuned H o H o H o 23

24 nce ed ote or AS iohas ent agan a ate cilte, inya erver als on) de after the exciting pulse has finished and the receiver does not detect any signal from the tag. Figure 25 shows the different parts of an acousto-magnetic label. The external case contains a plastic sleeve in which the sensible element, a strip of amorphous metal, is free to oscillate. Also included is a strip of a semi-hard magnetic material that is responsible Magnetoelastic resonance Electronic article surveillance systems (anti-theft tags) 16 Interrogation zone Interrogation signal Acousto-magnetic tag Response signal Plastic sleeve Magnetoelastic tag Magnetostrictive element Bias magnet Emitter Receiver Figure 24. Electronic Article Surveillance (EAS) system. activated Figure 25. Components of an acousto-magnetic EAS tag. The activ element is a magnetostrictive amorphous ribbon that is free to oscillat inside a plastic sleeve. The bias magnet is a semi-hard magnetic materia that can be easily magnetized to activate the tag and demagnetized t deactivate it. of biasing the sensible element and therefore of selectin its resonance frequency. Figure 26 resumes the operation o the system: In the activated state, the bias magnet is mag netized and the sample resonates at 58 khz, maintainin an oscillation when the exciting pulse stops. To deactivat the tag, the authorized operator demagnetizes the bias mag net (by applyingde-activated a decreasing-amplitude alternating 24 mag

25 Magnetoelastic resonance Oil viscosity sensor (for predictive maintenance) η (cst) 25

26 Outline Introduction Magnetism basics Magnetization process Soft magnetic materials Magnetic microsensors Magnetic field sensors Electronic compass Magneto-impedance sensors Magnetoelastic sensors Magnetoelastic effect Magnetoelastic resonance Oil viscosity sensor Magnetic nanodiscs for cancer therapy Magneto-mechanical actuation Magnetic vortex state Sub-100 nm vortex discs Nanodiscs in cancer cells 26

27 Magnetic nanodiscs for cancer therapy Magnetic nanoparticles in bio-medicine Magnetic Resonance Imaging (MRI) Drug delivery Hyperthermia Iron oxides, chemically produced. Patterned magnetic particles Great shape versatility Many different compositions Excellent reproducibility Produced by physical methods (vapor deposition, lithography, ) 27

28 Magneto-mechanical actuation Magneto-mechanical actuation of Permalloy discs with vortex state Kim et al, Nature Materials 9, (2010) 28

29 Magnetic Vortex state Peculiar magnetic behaviour in the nanoscale: no magnetic domains The completion between exchange and magentostatic energy produce different configurations Vortex state Magnetization process Large permeability and magnetization Null remanence high actuation capability no particle agglomeration 29

30 Sub-100 nm vortex discs Allow for intra-cellular magneto-mechanical actuation 1 µm external actuation 60 nm intra-cell actuation Fabrication of sub-100 nm permalloy discs Magnetic characterization In-vitro test of magneto-mechanical actuation 30

31 Sub-100 nm vortex discs Fabrication by Hole-mask colloidal lithography Use charged spheres to create a distribution of holes on a polymer 1) deposit a PMMA layer (spin coating) PMMA Si 2) charge surface with PDDA ) deposit charged spheres non-regular dense arrangement of nanospheres 31

32 Sub-100 nm vortex discs Fabrication by Hole-mask colloidal lithography 4) Ti sputtering 5) Tape stripping PMMA Si 6) Oxygen plasma PMMA etching Ti template of holes 32

33 Sub-100 nm vortex discs Fabrication by Hole-mask colloidal lithography 7) Py sputtering 8) PMMA removal Py nanodots on Si substrate 33

34 Sub-100 nm vortex discs Detachment from the substrate Use of Germanium as sacrificial layer 140 nm 60 nm 34

35 Sub-100 nm vortex discs Magnetic behaviour 1.0 M/M s R = 70 nm T = 50 nm µ H (mt) 0 35

36 Sub-100 nm vortex discs Magneto-mechanical actuation 36

37 Nanodiscs in cancer cells Interaction of microdiscs (R = 1!m, T = 60 nm) with human lung carcinoma cells {nanodiscs (R = 70 nm, T = 50 nm) Protocol of the in-vitro assays 37

38 Nanodiscs in cancer cells Asses the effect of the discs and the alternating magnetic field 38

39 Nanodiscs in cancer cells 2!m 140 nm Even without functionalization, discs are internalized by the cells 39

40 Nanodiscs in cancer cells Cytotoxicity After 24 h incubation, nearly 100% of cells with discs survival 40

41 Nanodiscs in cancer cells Magneto-mechanical actuation H = 10 mt f = 10 Hz t = 10, 30 min 41

42 Nanodiscs in cancer cells Magneto-mechanical treatment Cells with nanodiscs inside die after 30 min in perpendicular field 42

43 Nanodiscs in cancer cells Magneto-mechanical treatment Comparison of the effectiveness of the mechanical treatment Cell viability (%) MDs MF 10 min MDs MF 30 min MDs MF 30 min Nanodiscs MF 30 min Nanodiscs are more effective! 43

44 Summary Soft magnetic materials enable classical technologies but many new applications are continuously being developed. Large permeability is a key parameter for magnetic field sensors. Magnetic properties are highly coupled with other effects in soft magnetic materials. For instance, magneto-elasticity allows several sensing mechanisms. Nanotechnology largely benefits from soft magnetic materials. For example, magneto-mechanical actuation of magnetic nanodiscs with vortex state is studied for novel cancer therapies. 44

45 Acknowledgements Grupo de Magnetismo y Materiales Magnéticos 45