Understanding Magnetism and Magnetic Materials

1. Can be defines as: Phenomenon by which materials assert an attractive or repulsive force or influence on other materials Magnetic Materials includes -iron, some steels, lodestone minerals Principle applied in medicine- Magnetic Resonance Imaging From:http://en.wikipedia. org/wiki/Image:Modern_ 3T_MRI.JPG MAGNETISM

2. Magnetism force moving electrically charged particles Magnetic dipoles is similar to electric dipoles Represented by small bar of magnet with north and south poles (also represented by arrow) Within magnetic field, the force of the field exerts a torque that tends to orient the dipoles with the field Magnetic Dipoles

3. Magnetic Dipole Moment, m Magnetic Dipole Moment, m I = circulating current u n = unit vector coming out from area A

6. Origin of Magnetic Moments Each electron in an atom has magnetic moments that originate from two sources: One is related to its orbital motion around the nucleus; as a moving charge, electron -small current loop, -generating a very small magnetic field, -have a magnetic moment along its axis of rotation The other magnetic moment originates from this electron spin, which is directed along the spin axis Spin magnetic moments may be only in an up direction or in an antiparallel down direction

7. Do you know? Magnetic resonance (MR) imaging is founded on the manipulation of magnetic dipole moments in such a way that signals generated from these interactions that can be translated into visual images of the body. Figure Typical MR images of the head (left), neck (middle) and kidneys (right).

8. Magnetic Field Vectors

9. Magnetic Field Vectors Magnetic Field Strength, H Magnetic Flux Density, B Magnetic Permeability, Magnetization, M Magnetic Susceptibility, m

10. The externally applied magnetic field, i.e. the magnetic field strength, H . Magnetic Field Strength If the magnetic field is generated by solenoid consisting of: N= closely spaced turns, l =length, I= current magnitude The units of H are amperes per meter.

11. Magnetic Flux Density Magnetic flux density, B , represents the magnitude of the internal field strength within a substance that is subjected to an H field. Both B & H are field vectors, being characterized not only by magnitude, but also by direction in space. The magnetic field strength and flux density are related according to: The units for B are teslas The units for B are teslas

12. Magnetic Permeability Magnetic Permeability Magnetic permeability is define as the magnetic field per unit magnetizing field The permeability has dimensions of webers per amperemeter (Wb/A-m) or henries per meter (H/m). In a vacuum, where o is the permeability of a vacuum, 4 10 -7 (1.257 10 -6 ) H/m.

13. Relative permeability r of a medium is the fractional increase in the magnetic field with respect to the field in free space when a material medium is introduced. Magnetic Permeability Magnetic Permeability

14. Magnetization Another field quantity, M , called the magnetization of the solid, is defined by the expression In the presence of an H field, the magnetic moments within a material tend to become aligned with the field & to reinforce it by virtue of their magnetic fields; the term o M The magnitude of M is proportional to the applied field as follows:

15. Magnetic Susceptibility Magnetic Susceptibility Magnetic susceptibility m indicates the ease with which the material becomes magnetized under an applied magnetic field m is unitless

16. Represented by: B = Bohr Magneton = 9.27 x 10 -24 A m 2 Bohr magneton ( B ) is a useful elementary unit of magnetic moment on the atomic scale. It is equal to the magnetic moment of one electron spin along an applied magnetic field B =e/2m e Bohr Magneton Bohr Magneton e is the elementary charge e is the elementary charge is the reduced Plancks constant is the reduced Plancks constant m e is the electron rest mass m e is the electron rest mass

17. a form of magnetism that is non-permanent and occurs only in the applied field with the direction opposite the applied field Diamagnetism = a form of magnetism that is non-permanent and occurs only in the applied field with the direction opposite the applied field Note: r < 1 (slightly) : m is negative and in the order of 10 -5 magnetism does not exist with absence of H (random arrangement of dipoles moments), but exist under applied field (H) Paramagnetism = magnetism does not exist with absence of H (random arrangement of dipoles moments), but exist under applied field (H) Note: r > 1 : m is small and positive in the order of 10 -5 to 10 -2 Diamagnetic and Paramagnetic materials non-magnetic Diamagnetism and Paramagnetism

18. B vs H for diamagnetic and paramagnetic materials Diamagnetism : Paramagnetism : Ferromagnetism

19. Diamagnetics Paramagnetics Material m Material m Aluminum Oxide Copper Gold Mercury Silicon Silver Sodium Chloride Zinc -1.81x10 -5 -0.96x10 -5 -3.44x10 -5 -2.85x10 -5 -0.41x10 -5 -2.38x10 -5 -1.41x10 -5 -1.56x10 -5 Aluminum Chromium Chromium Chloride Manganese Sulfate Molybdenum Sodium Titanium Zirconium 2.07x10 -5 3.13x10 -4 1..51x10 -3 3.70x10 -3 1.19x10 -4 8.48x10 -6 1.81x10 -4 1.09x10 -4 Room Temperature m for Diamagnetic and Paramagnetic Materials Diamagnetism and Paramagnetism

20. Ferromagnetism = phenomenon in certain (metallic) materials that possess a permanent magnetic moment in the absence of H Domain = Area (volume) of a material that the mutual spin alignment exist Saturation Magnetization (M s ) The maximum possible magnetization Ferromagnetism

21. Antiferromagnetism = the alignment of the spin moments of the neighboring atoms or ions in exactly opposite direction MnO = Antiferroelectric Mn 2+ Spin-origin magnetic moment Align antiparallel in crystal structure O 2- No net magnetic moment Cancellation of m s , m l Antiferromagnetism and Ferrimagnetism

22. Ferrimagnetism = a permanent magnetization in materials that is very similar to ferromagnetism but originates from different source of the net magnetic moment Ferrimagnetic Material : Cubic Ferrites : MFe 2 O 4 : M = one of the metallic elements Prototype Fe 3 O 4 (magnetite or lodestone) Inverse Spinel Structure Fe 2+ O 2- - (Fe 3+ ) 2 (O 2- ) 3 O 2- = Magnetically neutral Fe 2+ = Net spin magnetic moment = 4 B Fe 3+ = Net spin magnetic moment = 5 B Antiferromagnetism and Ferrimagnetism

24. Ferrofluid Ferrofluid Ferrofluids or Magnetic Fluids are fluids with magnetic nanoparticle suspended in a liquid medium The particles are generally coated to prevent magnetostatic interactions which would cause the particles to cluster together From- http://www.ucl.ac.uk/ ~ucfbpmb/ferrofluid% 20copy.jpg

25. Biomedical Applications of Magnetic Materials Biomedical Applications of Magnetic Materials Abnormalities in body tissues and organs can be detected on the basis of the production of cross- sectional images using Magnetic Resonance Imaging (MRI) Chemical analysis of body tissues is also possible using Magnetic Resonance Spectroscopy (MRS). Chemical analysis of body tissues is also possible using Magnetic Resonance Spectroscopy (MRS). Magnetic Drug Targeting- applies nanoparticles to target drugs and genes to specific sites in vivo Magnetic Drug Targeting- applies nanoparticles to target drugs and genes to specific sites in vivo Using this method, this can enhance drug and gene uptake at the sites Using this method, this can enhance drug and gene uptake at the sites Also known as magnetic target carriers (MTC) Also known as magnetic target carriers (MTC)

26. A chitosan "mothership" capsule (light blue) attaches and delivers drug-filled vesicles (dark blue) to a tumor. This capsule may be targeted to tumor cells either by antibodies (the Y- shaped spines) on its outer surface or by magnetic nanoparticles (dark red) inside. These two targeting systems effectively act as navigators, taking the capsules "along for the ride" to precise locations where the drugs are needed. Dowling et al. has found, they can then be guided to specific locations in the body with an electromagnetic field. www.bioe.umd.edu/fischell-fellowship/dowling.html

27. Magnetic force bioreactor for tissue engineering The magnetic force bioreactor is designed to apply forces directly to the cell membrane by coupling biocompatible magnetic nano- and microparticles to the membrane surface From-http://www.maths.nottingham.ac.uk/personal/pmzsjf/Image2.gif

28. Other applications: MRI Contrast Enhancement MR delivers excellent soft-tissue contrast, however, assistance from contrast media (which usually from paramagnetic agent) is done to obtain better image. Figure shows brain images both before and after contrast allow disruptions in the blood-brain barrier to be investigated From: www.hull.ac.uk/mri/lectures/gpl_page.html