Lecture 10 ECEN Chapter 3 and 4 Frank Barnes 1

Magnetic Materials 1. Diamagnetic 2. Paramagnetic 3. Ferromagnetic 4. Antiferromagnetic 2

Diamagnetic Materials 1. Electron spins are paired one up, one down 2. The magnetic moments are from the orbital motion of the electrons. The sign of the magnetic moment is negative. 3.Most biological materials are diamagnetic and these materials are weakly repelled by in a magnetic field gradient. 4. Superconductors are diamagnetic and you can float a magnetic above a superconducting plate 3

A Superconductor is a perfect magnetic shield. 1 4

The Moses Effect 5

Paramagnetic Materials 1 Paramagnetic materials are attracted by a magnetic field gradient. 2. These materials have net magnetic moments but on the average to zero as a result of the thermal energy. 3. At low fields the net magnetic moment is proportional to the applied magnetic field. 4. The magnetic moment saturates at high fields. Pierre Curie and is known as Curie ’s law: M =H ¼ X ¼ C =T – where M is the magnetization, H is the applied magnetic field, X is the magnetic susceptibility, – T is the temperature, and C is the Curie constant and is related to the magnetic proper ties of the material 6

Magnetic Field Effects 7 Paramagnetic materials have permeate magnetic moments Spin Alignment for Paramagnetic Materials

Ferromagnetic Materials 1 There are coupled spins in an inner shell of atoms such as iron. In Iron the exchange energy parallels four electron spins. This is a strong enough magnetic moment to align blocks of atoms. 2. The magnetic susceptibility is positive. 3. Ferromagnetic material have magnetic moments even after the field is removed and hysteresis below a given temperature. 8

Ferromagnetic Spins Align 9

Antiferromagnetic Material These materials can have net magnetic moment. 10

Ferrimagnetic Materials This the case for Fe 3 O 4 which had Fe 2+ and Fe 3+ in the lattice. This is a bio manufactured material 11

Temperature Dependence of Ferromagnetic Materials 1 12

Energy Barrier for Superparamagnetic Material 1 Spins flip as a group with thermal energy ≈10 -9 seconds Remanent magnetic field 13

Biological Magnet FIGURE 4.7 Model of the ferritin protein showing the peptide subunits and iron transport channels. (From wustl.edu/edudev/LabTutorials/Ferritin/FerritinTutorial.html. With permissionwww.chemistry.) 14

Iron in the Body In organisms, iron is stored as the mineral ferrihydrite (5Fe 2 O 3 9H 2 O) with in the iron storage protein ferritin. It consists of a 12-nm hollow spherical protein shell made up of 24 subunits (Figure 4.7). The core of ferritin protein is 8 nm in diameter, and it can hold up to 4500 iron atoms in the form of ferrihydrite. Iron is transported into and out of the core through three- and fourfold channels in the shell. During transport, highly toxic Fe(II ) is oxidized to Fe( III) for storage as ferrihydrite (Harrison and Arosio, 1996). Ferrihydrite is a superparamagnetic antiferromagnet 15

Magnetite (Fe 3 O 4 ) a ferromagnetic iron oxide Transmission electron micrograph of the magnetotactic bacterium MS-1 (top). (From rfrankel/mtbphoto.html ) Biogenic magnetite extracted from the human hippocampus (bottom). (From Schultheiss-Grassi, PP, R Wessiken, and J Dobson (1999) Biochim. Biophys. Acta 1426 : 212–216. With permission.) 16

Hemoglobin 17 Figure 7 The structure of hemoglobin, μ eff = 5.35 per heme group. [Wadas 1991].