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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 Metals Structure – PropertIES APPLICATIONS

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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

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