アルミニウムは磁性を持つか？

You try to stick a magnet to aluminum—it slides off. But does that mean it’s not magnetic at all?

Aluminum is considered non-magnetic because it does not attract magnets under normal conditions due to its weak interaction with magnetic fields.

However, there’s more to it than meets the eye—especially when we look deeper into physics and materials science.

What magnetic properties does aluminum have?

Aluminum doesn’t behave like iron or nickel, but that doesn’t mean it lacks magnetic properties entirely.

Aluminum is classified as paramagnetic, meaning it has weak and temporary magnetic properties when exposed to an external magnetic field.

Magnetic Classifications

There are three main types of magnetism:

1. Ferromagnetic: Strong attraction (e.g., iron, cobalt)
2. Paramagnetic: Weak, temporary attraction (e.g., aluminum, magnesium)
3. Diamagnetic: Weak repulsion (e.g., copper, bismuth)

Aluminum is paramagnetic. It slightly aligns with magnetic fields, but the effect is so weak that it’s not noticeable in everyday use.

No Permanent Magnetism

Once the external magnetic field is removed, aluminum returns to its original state. It does not retain any magnetization like iron does.

Why is aluminum considered non-magnetic?

When people say something is “non-magnetic,” they usually mean it doesn’t stick to a magnet.

Aluminum is labeled non-magnetic because its weak paramagnetic behavior is too subtle to observe without scientific tools.

Lack of Unpaired Electrons

Magnetism in metals is often due to unpaired electrons in their atomic structure. Aluminum has all its electrons paired, so it doesn’t produce a magnetic field.

Crystal Structure

Aluminum has a face-centered cubic structure that doesn’t support magnetic domain alignment. This limits its ability to become magnetized.

No Observable Force

When you bring a magnet close to aluminum, there’s no visible reaction. For consumers and engineers, this means it behaves like a “non-magnetic” material in practical applications.

Can aluminum become magnetic under special conditions?

Yes, but only temporarily and under extreme conditions.

Aluminum can show stronger magnetic effects under certain conditions such as very high magnetic fields, cryogenic temperatures, or when it’s moving relative to a magnetic field.

Moving Aluminum and Eddy Currents

When aluminum moves through a magnetic field, it creates circular electric currents called eddy currents. These generate their own magnetic field that repels the magnet. This effect is seen in:

• Magnetic braking systems
• Induction heating
• Roller coasters and trains

Even though the material isn’t magnetic, its motion in a magnetic field makes it “appear” magnetic.

Low-Temperature Behavior

At temperatures near absolute zero, aluminum shows slightly more noticeable paramagnetic effects, but still not enough to become ferromagnetic.

Not Magnetizable

Even in extreme lab conditions, aluminum cannot hold magnetism. It always returns to its original, neutral state.

How to test magnetism of metals?

You don’t need a lab to check if a metal is magnetic—just some basic tools.

You can test a metal’s magnetism using a neodymium magnet, checking for attraction or repulsion, or using electromagnetic induction setups for deeper analysis.

Simple Magnet Test

Hold a strong magnet (like neodymium) close to the metal:

• If it sticks hard: It’s likely ferromagnetic
• If nothing happens: It could be non-magnetic or weakly paramagnetic

Movement Test (Eddy Currents)

Slide a magnet over a slanted aluminum surface. You’ll feel 抵抗 または slowdown. This shows eddy current generation—not magnetism, but still magnetic interaction.

Use of a Gauss Meter

For more precise results, a gauss meter can measure magnetic fields near the metal. It detects if a metal influences the magnetic field, even if it’s not attracted.

結論

Aluminum is non-magnetic in daily use, but scientifically it’s classified as paramagnetic. Though it doesn’t attract magnets like iron, it still interacts with magnetic fields in unique ways, especially when moving.