Magnetism is a fundamental property of materials, and different substances interact with magnets in various ways. Some materials are strongly attracted to magnets, while others are only weakly influenced or even repelled by them. The materials that are feebly repelled by a magnet are called diamagnetic materials.
This topic explores diamagnetic materials, their properties, examples, and applications, as well as the science behind their weak repulsion by magnets.
Understanding Magnetic Properties of Materials
Types of Magnetic Materials
Materials can be classified into three major categories based on their interaction with magnetic fields:
- Ferromagnetic Materials – Strongly attracted to a magnet (e.g., iron, nickel, cobalt).
- Paramagnetic Materials – Weakly attracted to a magnet (e.g., aluminum, platinum).
- Diamagnetic Materials – Feebly repelled by a magnet (e.g., copper, gold, bismuth).
Since the focus of this topic is on diamagnetic materials, let’s explore their unique properties and characteristics.
What Are Diamagnetic Materials?
Definition of Diamagnetic Materials
Diamagnetic materials are substances that develop a weak magnetic field in opposition to an external magnetic field. This causes them to be slightly repelled by a magnet.
Unlike ferromagnetic or paramagnetic materials, diamagnetic materials do not retain magnetization once the external magnetic field is removed. This means they always exhibit a repelling effect when placed near a magnet.
Why Are They Repelled by Magnets?
The repulsion of diamagnetic materials is due to Lenz’s Law, which states that when an external magnetic field is applied, the electrons in the material adjust their motion to generate an opposing field. This results in a very weak repulsive force.
This phenomenon is common in materials that have completely filled electron shells, meaning there are no unpaired electrons to create a net magnetic moment.
Examples of Diamagnetic Materials
Common Diamagnetic Substances
Here are some examples of materials that are feebly repelled by a magnet:
| Material | Common Uses |
|---|---|
| Bismuth | Magnetic levitation experiments, shielding in scientific instruments |
| Copper | Electrical wiring, coins, plumbing |
| Gold | Jewelry, electronics, dentistry |
| Silver | Jewelry, electrical conductors, photography |
| Lead | Radiation shielding, batteries |
| Graphite | Pencil leads, lubricants, batteries |
| Water | Biological systems, living organisms |
| Mercury | Thermometers, barometers, electrical switches |
| Quartz | Watches, electronics, optical devices |
| Carbon (diamond) | Jewelry, industrial cutting tools |
Each of these materials exhibits weak magnetic repulsion when placed near a strong magnetic field.
Experimental Demonstration of Diamagnetism
The Bismuth Experiment
One of the best ways to observe diamagnetism is with bismuth. Bismuth has one of the strongest diamagnetic effects.
Steps to Observe Diamagnetism in Bismuth:
- Take a piece of bismuth metal and place it near a strong neodymium magnet.
- Observe how the bismuth piece moves slightly away from the magnet.
- If small flakes of bismuth are suspended in water, they will move away from the magnet as well.
This experiment clearly shows the weak repulsion characteristic of diamagnetic materials.
Floating Graphite Experiment
Another demonstration involves graphite, which is diamagnetic but very light. If a small piece of pyrolytic graphite is placed over strong neodymium magnets, it will levitate slightly due to diamagnetic repulsion.
This effect is used in scientific research and in the development of frictionless magnetic levitation technology.
Properties of Diamagnetic Materials
1. Weak Magnetic Repulsion
Diamagnetic materials are very weakly repelled by magnets, and this effect is usually difficult to notice unless a strong magnetic field is applied.
2. No Permanent Magnetization
Unlike ferromagnetic materials, diamagnetic substances do not retain magnetism once the external field is removed.
3. Present in Everyday Materials
Many common substances, including water, plastic, and even living organisms, exhibit diamagnetism, though the effect is too weak to notice in daily life.
4. Can Exhibit Magnetic Levitation
Some diamagnetic materials, like bismuth and pyrolytic graphite, can exhibit magnetic levitation when placed over strong magnets.
Applications of Diamagnetic Materials
1. Magnetic Levitation (Maglev) Technology
Diamagnetic materials like graphite and bismuth are used in experiments for magnetic levitation. Some high-speed trains (Maglev trains) use diamagnetic properties to reduce friction.
2. Scientific Instruments and Shielding
- Bismuth is used in scientific instruments to shield magnetic fields.
- Lead is used in nuclear shielding due to its ability to block radiation.
3. Biomedical Applications
- Diamagnetic properties play a role in MRI (Magnetic Resonance Imaging) technology, where human tissues (mostly water-based) exhibit weak diamagnetism.
- Research on blood flow using magnetic fields considers the diamagnetic nature of red blood cells.
4. Electrical and Electronic Applications
- Copper and silver, both diamagnetic, are widely used in electrical wiring and circuits due to their excellent conductivity.
5. Space and Aerospace Research
Diamagnetic effects are studied for potential applications in space travel, including low-friction movement in zero-gravity environments.
Comparison of Magnetic Properties
To better understand how diamagnetic materials compare with other types, here’s a comparison:
| Property | Diamagnetic | Paramagnetic | Ferromagnetic |
|---|---|---|---|
| Interaction with Magnet | Feebly repelled | Weakly attracted | Strongly attracted |
| Permanent Magnetization? | No | No | Yes |
| Magnetic Field Retention | No | No | Yes |
| Examples | Bismuth, Copper, Gold | Aluminum, Platinum, Oxygen | Iron, Nickel, Cobalt |
From this table, it is clear that diamagnetic materials are unique in their repelling behavior, making them different from paramagnetic and ferromagnetic materials.
Diamagnetic materials are feebly repelled by a magnet due to the formation of an opposing induced magnetic field. Unlike ferromagnetic or paramagnetic materials, diamagnetic substances do not retain magnetization and exhibit a very weak repulsion.
Common examples of diamagnetic materials include bismuth, copper, gold, silver, graphite, water, and mercury. These materials have applications in magnetic levitation, electrical engineering, biomedical technology, and scientific research.
While diamagnetism is often overlooked due to its weak effects, it plays a significant role in modern physics, engineering, and emerging technologies. Understanding these materials helps in the advancement of magnetically controlled systems and futuristic applications.