Magnetic Metals Structure – PropertIES APPLICATIONS

1. Magnetic MetalsStructure –PropertIES APPLICATIONS Howard H. Liebermann, Ph.D.

2. Fundamentals • Structure of Metals • On atomic level, regular arrangement of atoms immersed in “sea” of “free electrons”. • Results of this: • Metallic bond • Electrical, thermal conductivity • Ductility • Typical arrangements of atoms: • BCC, FCC, HCP • Atypical arrangement of atoms: • Amorphous H.H. Liebermann

3. Cubic Crystal Systems FCC Simple Cube BCC H.H. Liebermann

4. Basic Magnetics • Electron has negative charge • Orbiting of electrons about atom induces magnetic moment (vector) • These magnet moments can interact • with one another • with an external applied magnetic field • Extent of interaction determines what kind of magnetism (exchange vs. anisotropy) H.H. Liebermann

5. Magnetic Axes in BCC (Fe) H.H. Liebermann

6. Magnetic Axes in FCC (Ni) H.H. Liebermann

7. Kinds of Magnetism • Ferromagnetism: magnetic spin interaction is large – applied external magnetic field doesn’t affect this • Paramagnetism: magnetic spins tend to align in the direction of applied field • Diamagnetism: magnetic spins tend to align in the direction away from applied field H.H. Liebermann

8. Some Magnetic Characteristics • Exchange - strong interaction between magnetization vectors • Anisotropy – preferential direction for magnetization vector in a material • Magnetostriction – interaction between stress (applied, residual, etc.) and magnetization vector direction H.H. Liebermann

9. Curie Temperature • Temperature above which sample magnetization ceases. • True for ferromagnetic, paramagnetic, etc. • Potential in sensor applications. H.H. Liebermann

10. Exchange Interaction • Quantum mechanical effect: • Tendency for adjacent magnetic vectors to align directionally. • Affected by thermal energy. H.H. Liebermann

11. Magnetic Anisotropy • Origin: • Tropy – direction • Iso – constant • An – not • Conclusion – not constant with direction in an alloy. • Magnetic anisotropy result of: • Crystal structure of alloy. • Shape of sample being tested. • Magnetic field induced. H.H. Liebermann

12. Magnetostriction • Link between change in magnetic sample dimensions (stress) and applied magnetic field. • Reciprocity abounds. • Stress can result from numerous causes: • Forces applied to magnetic sample. • Residual forces resulting from cooling on heat treating. • Forces arising during use of a device. H.H. Liebermann

13. Schematic Example • Iron • Cobalt • Iron + Cobalt H.H. Liebermann

14. Magnetic Domain Wall Width w~ ε K H.H. Liebermann

15. Magnetization Loop H.H. Liebermann

16. Magnetic Domain Wall Motion • No external field (applied, residual, etc.) and magnetization vector direction • Low external field • High external field H.H. Liebermann

17. Other Domain Wall Mechanisms • Rotational • Reverse domain nucleation • Eddy current generation • Magnetic losses • Electrical losses • Heat losses H.H. Liebermann

18. Hard vs. Soft Magnets H.H. Liebermann

19. Applications of Magnetic Mat’ls H.H. Liebermann

20. Applications of Hard Magnets H.H. Liebermann

21. Applications of Hard Magnets H.H. Liebermann

22. Applications of Soft Magnets H.H. Liebermann

23. Applications of Soft Magnets H.H. Liebermann

24. Summary • Wide variety of materials/applications. • Elementary concepts of materials science as they apply to magnetic materials. • Aspects of alloy design (chemistry) and resulting effects on magnetic properties. H.H. Liebermann