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# Nano materials

Nano materials
Published on: Mar 5, 2016
Published in: Engineering

#### Transcripts - Nano materials

• 1. Magnetic Properties Iron single crystal photomicrographs magnetic domains change shape as a magnetic field (H) is applied. domains favorably oriented with the field grow at the expense of the unfavorably oriented domains.
• 2. Forces can be represented by imaginary lines grouped as fields c18f01 Basic Concepts Magnetic forces appear when moving charges Magnetic field lines of force around a current loop and a bar magnet.
• 3. MAGNETIC DIPOLES The magnetic moment represented by a vector
• 4. c18f03 Magnetic Field Vectors magnetic field strength (H) & magnetic flux density (B) Magnetic flux density H = B  B = H 0 0  relative permeability   0 r =  magnetization = + 0 0B  H  M M = H m  magnetic susceptibility = -1 m r   NI l Magnetic field strengthH =
• 5. Origins of Magnetic Moments: Responds to quantum mechanics laws Two main contributions: (a) an orbiting electron and (b) electron spin. Bohr magneton (B) Most fundamental magnetic moment B = ±9.27x10-24 A-m2 The spin is an intrinsic property of the electron and it is not due to its rotation
• 6. c18f05 18.3 Diamagnetism and Paramagnetism Diamagnetic material in the presence of a field, dipoles are induced and aligned opposite to the field direction. Paramagnetic material
• 7. The flux density B versus the magnetic field strength H for diamagnetic and paramagnetic materials.  B = 0H + 0M = 0H + 0mH   = 0(1 + m)
• 8. FERROMAGNETISM mutual alignment of atomic dipoles even in the absence of an external magnetic field. coupling forces align the magnetic spins B H M =  +    0 0 B M 0 Domains with mutual spin alignment B grows up to a saturation magnetization Ms with a saturation flux Bs = Matom × Natoms (average moment per atom times density of atoms) Matom = 2.22B, 1.72B, 0.60B for Fe, Co, Ni, respectively
• 9. 1986: superconductivity discovered in layered compound La2-xBaxCuO4 with a transition T much higher than expected. Little was known about copper oxides c18f08 Antiferromagnetism & Ferrimagnetism ANTIFERROMAGNETISM Antiparallel alignment of spin magnetic moments for antiferromagnetic manganese oxide (MnO) At low T Above the Neel temperature they become paramagnetic Parent materials, La2CuO4, and YBa2Cu3O6, demonstrated that the CuO2 planes exhibit antiferromagnetic order. This work initiated a continuing exploration of magnetic excitations in copper-oxide superconductors, crucial to the mechanism of high-temperature superconductivity.
• 10. FERRIMAGNETISM spin magnetic moment configuration for Fe2+ and Fe3+ ions in Fe3O4. Above the Curie temperature becomes paramagnetic
• 11. 18tf03
• 12. 18.6 The Influence of Temperature on magnetic Behavior TC: Curie temperature (ferromagnetic, ferrimagnetic) TN: Neel temperature (antiferromagnetic) material become paramagnetic
• 13. c18f11 18.7 Domains and Hysteresis Domains in a ferromagnetic or ferrimagnetic material; arrows represent atomic magnetic dipoles. Within each domain, all dipoles are aligned, whereas the direction of alignment varies from one domain to another. Gradual change in magnetic dipole orientation across a domain wall.
• 14. c18f13 B versus H ferromagnetic or ferrimagnetic material initially unmagnetized Domain configurations during several stages of magnetization Saturation flux density, Bs Magnetization, Ms, initial permeability i
• 15. Magnetic flux density versus magnetic field strength ferromagnetic material subjected to forward and reverse saturations (S & S’). hysteresis loop (red) initial magnetization (blue) remanence, Br coercive force, Hc
• 16. Comparison magnetic versus nonmagnetic
• 17. Superconductivity Temperature dependence of the electrical resistivity for normally conducting and superconducting materials in the vicinity of 0 K.
• 18. Critical temperature, current density, and magnetic field boundary separating superconducting and normal conducting states (schematic).
• 19. Representation of the Meissner effect. While in the superconducting state, a body of material (circle) excludes a magnetic field (arrows) from its interior. The magnetic field penetrates the same body of material once it becomes normally conductive.
• 20. SUMMARY • A magnetic field can be produced by: --putting a current through a coil. • Magnetic induction: --occurs when a material is subjected to a magnetic field. --is a change in magnetic moment from electrons. • Types of material response to a field are: --ferri- or ferro-magnetic (large magnetic induction) --paramagnetic (poor magnetic induction) --diamagnetic (opposing magnetic moment) • Hard magnets: large coercivity. • Soft magnets: small coercivity. • Magnetic storage media: --particulate g-Fe2O3 in polymeric film (tape or floppy) --thin film CoPtCr or CoCrTa on glass disk (hard drive)