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Magnetic Metals Structure – PropertIES APPLICATIONS. Howard H. Liebermann, Ph.D. 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
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Magnetic MetalsStructure –PropertIES APPLICATIONS Howard H. Liebermann, Ph.D.
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
Cubic Crystal Systems FCC Simple Cube BCC H.H. Liebermann
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
Magnetic Axes in BCC (Fe) H.H. Liebermann
Magnetic Axes in FCC (Ni) H.H. Liebermann
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
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
Curie Temperature • Temperature above which sample magnetization ceases. • True for ferromagnetic, paramagnetic, etc. • Potential in sensor applications. H.H. Liebermann
Exchange Interaction • Quantum mechanical effect: • Tendency for adjacent magnetic vectors to align directionally. • Affected by thermal energy. H.H. Liebermann
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
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
Schematic Example • Iron • Cobalt • Iron + Cobalt H.H. Liebermann
Magnetic Domain Wall Width w~ ε K H.H. Liebermann
Magnetization Loop H.H. Liebermann
Magnetic Domain Wall Motion • No external field (applied, residual, etc.) and magnetization vector direction • Low external field • High external field H.H. Liebermann
Other Domain Wall Mechanisms • Rotational • Reverse domain nucleation • Eddy current generation • Magnetic losses • Electrical losses • Heat losses H.H. Liebermann
Hard vs. Soft Magnets H.H. Liebermann
Applications of Magnetic Mat’ls H.H. Liebermann
Applications of Hard Magnets H.H. Liebermann
Applications of Hard Magnets H.H. Liebermann
Applications of Soft Magnets H.H. Liebermann
Applications of Soft Magnets H.H. Liebermann
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