Magnetic Fields in Matter

Hall Effect

What it shows:

When a magnetic field is applied perpendicular to a conductor carrying current, a potential difference is observed between points on opposite sides of the conductor. This happens because the magnetic field deflects the moving electrons (Lorentz force) to the edge of the conductor and the altered charge distribution generates a transverse electric field.

How it works:

The conductor is a small bar (11mm × 2mm × 2mm) of germanium (p-type?). Current (18 mA) is made to flow down the length of the bar by a 3 volt potential...

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Magnetic Bubbles

What it shows:

A thin wafer of Ferromagnetic Garnet reveals its magnetic domain alignment as light and dark serpentine patterns when viewed between crossed Polarizers. These domains can be flipped by an external magnetic field, changing the pattern structure.

How it works:

The magnetic bubble apparatus consists 1 of a thin (8-12μm) single crystal film of Ferromagnetic Garnet (FMG) sandwiched between a pair of crossed Polaroids. The FMG crystals are magnetically anisotropic, that is, they have a strong tendency to orient...

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The Barkhausen Effect

What it shows:

The magnetization of a ferromagnetic substance occurs in little jumps as the magnetic moments of small bunches of atoms, called domains, align themselves with the external field. We can actually "hear" the switching of these domains by amplifying the currents induced in a coil that surround the ferromagnetic material.

How it works:

We use two 10mH coils mounted back-to-back to cut out AC noise. The samples, listed in Fig.1 are in wire form, about 3-5cm in length and pushed through corks so they can sit...

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Paramagnetism of Oxygen

What It Shows

A large magnet with a small cylindrical gap allows a stream of liquid nitrogen to pass over and through. Poured liquid oxygen hangs between the poles in the strong field until it boils away.

How It Works

Pour the liquid nitrogen first, slowly over the pole pieces. The result is nothing but vapor condensation and crackling plexiglas; the liquid does not interact with the large magnetic field.

Next pour the liquid oxygen slowly over the pole pieces, and it collects in the gap between the poles. It might take two or three short pours to get the...

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Diamagnetic Levitation

What it shows:

Stable levitation of one magnet by another is usually prohibited by Earnshaw's Theorem, but the introduction of diamagnetic material at special locations can stabilize such levitation. The demonstration is a replica of an experiment described by M.D. Simon and A.K. Geim1 and is pictured in the photograph. The illustration is from their paper.

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Para and Diamagnetism

What it shows: 

The behavior of a substance in a non-uniform magnetic field will depend upon whether it is ferromagnetic, paramagnetic or diamagnetic. Here we test different substances to see how they are influenced by a magnetic field.

How it works: 

We have a collection of samples (listed in table 1) that exhibit well the three magnetic properties. Diamagnetic substances have a negative relative permeability (susceptibility); paramagnetic substances have positive.

Ferromagnetic substances have...

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