Outline How is ferromagnetism manifested? What are the types of magnetism? What is Fe 3 O 4 – spinel? What is nanoscience? How do we make ferrofluids?

We will have a Monday class next week Turn in extra credit Writing exercises will be returned Possible chance for regaining lost points SRTI evaluations

SS SSN NN N The field of a force – a property of the space in which the force acts Magnetic field attraction repulsion

θ Interaction with magnetic field m = AIn m = pd +p -p d τ = m B sinθ B θ aligning torque:

Magnetic field (force lines) Magnetic field is not a central field (no free magnetic charges) SN F

Behavior of magnetic materials T Neel T Curie Ferromagnet, Ferrimagnet Antiferromagnet Paramagnet Magnetization (  m or  B or M) Temperature

Types of bulk magnetism FerromagnetismAntiferromagnetism Ferrimagnetism Large M (1-5  B / atom) Small M (10 -3  B / atom) Large M (1-5  B / atom) H Small M (10 -3  B / atom) Paramagnetism

Development of permanent (hard) magnets M M Hard magnetsSoft magnets

What is nanoscience?

Contacts on a 60nm bismuth wire to study motion of single defects (kmf.pa.msu.edu/Research/resrch04.asp )kmf.pa.msu.edu/Research/resrch04.asp ZnO nanowire UV lasers of about 100nm diameter and 10mm length synthesized at Berkeley. (Yang et al, Science, 292, p. 1897, 2001). ZnO nanowire UV lasers of about 100 nm diameter and 10  m length synthesized at Berkeley. (Yang et al, Science, 292, p. 1897, 2001)

Radius rules CN Relative radius Void geometryPolyhedron name 2<15.5%LinearLine 315.5%TriangularTriangle 425.5%TetrahedralTetrahedron 641.4%OctahedralOctahedron 873.2%Cubic (BCC)Cube 12100%Cuboctahedral (HCP, CCP)Cuboctahedron A sphere of this size (relative to the lattice of size of its neighbors) is just able to touch all off its neighbors for the void geometries below. Similar considerations govern the formation of more complex structural arrangements

Arrangements of nanoparticles mimics arrangements of atoms

Some arrangements are very complex

Electronic and magnetic materials can be combined into sophisticated devices

Magnetite Magnetite vs. lodestone General spinel formula: AB 2 O 4 A = 2+ metal, B = 3+ metal 1/2 of octahedral holes, 1/8 of tetrahedral holes filled on an approximate FCC oxygen lattice Fe 3 O 4 1 Fe Fe 3+ Inverse spinel B(AB)O 4 Ferrimagnetic ordering at ~850K Fe 3 O 4 Synthesis: 2 FeCl 3 + FeCl NH 3 + 4H 2 O --> Fe 3 O NH 4 Cl

Magnetite (Fe 3 O 4 ) Unit cell: A-sites (8 Fe 3+ ) B-sites (8 Fe 3+ and 8 Fe 2+ ) Ferrimagnetism Normal Spinel (ZnFe 2 O 4 )Inverse Spinel (Fe 3 O 4 ) AB Zn 2+ Fe 3+ AB Fe 2+ => 5µB5µB 5µB5µB 4µB4µB

Development of permanent (hard) magnets Magnetic energy (Gauss / m 3 ) Steel Magnetic energy (Gauss / m 3 ) Steel Nd 2 Fe 14 B M M

Ferrofluids of ~10nm ferrite particles

Ferrofluids

Types of bulk magnetism FerromagnetismAntiferromagnetism Ferrimagnetism Large M (1-5  B / atom) Small M (10 -3  B / atom) Large M (1-5  B / atom) H Small M (10 -3  B / atom) Paramagnetism

FerromagnetismAntiferromagnetism Ferrimagnetism H Canted Antiferromagnetism FerromagnetismAntiferromagnetism Ferrimagnetism H Canted Antiferromagnetism

FerromagnetismAntiferromagnetism H FerromagnetismAntiferromagnetism H Ferrimagnetism Paramagnetism

FerromagnetismAntiferromagnetism Ferrimagnetism Large M (1-5  B / atom) Small M (10 -3  B / atom) Large M (1-5  B / atom) H Small M (10 -3  B / atom) Paramagnetism Types of magnetism

Ferrofluid topics Magnetic dipoles, not monopoles like charges Field gradient - emphasized by magnetic field lines A “test dipole” will aligns itself parallel to magnetic field lines

Development of permanent (hard) magnets M M