Magnetic Metals Structure – PropertIES APPLICATIONS

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 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

Magnetic Metals Structure – PropertIES APPLICATIONS