Magnetic susceptibility is an essential concept in electromagnetism and material science. It describes how a material responds to an external magnetic field. In the case of diamagnetic substances, the magnetic susceptibility is negative, meaning they develop a weak opposing magnetic field when placed in an external field.
In this topic, we will explore what magnetic susceptibility (Xâ and Xâ) means for diamagnetic materials, how it is measured, and its significance in different scientific and industrial applications.
Understanding Magnetic Susceptibility
What Is Magnetic Susceptibility?
Magnetic susceptibility (Ï) is a dimensionless quantity that determines how a material responds to an external magnetic field. It is defined as:
Where:
- M = Magnetization (magnetic moment per unit volume)
- Ï = Magnetic susceptibility
- H = Applied external magnetic field
For diamagnetic substances, Ï is negative, which means they create an opposing field that slightly repels the external magnet.
Types of Magnetic Susceptibility (Xâ and Xâ)
For diamagnetic substances, Xâ and Xâ represent different aspects of susceptibility:
- Xâ (Static Susceptibility) – It refers to the material’s response when exposed to a constant magnetic field.
- Xâ (Dynamic Susceptibility) – It describes how the material reacts when exposed to a changing or alternating magnetic field over time.
Understanding these two forms of susceptibility is crucial in fields like quantum mechanics, electromagnetism, and material science.
Magnetic Behavior of Diamagnetic Substances
How Do Diamagnetic Materials Respond to a Magnetic Field?
Diamagnetic substances exhibit weak repulsion when placed near a magnet. This happens because the electrons in the atoms adjust their motion to generate an induced magnetic field in the opposite direction.
This reaction follows Lenz’s Law, which states that an induced current will always oppose the change that caused it. As a result, diamagnetic materials have:
- A negative magnetic susceptibility
- A weak repulsive force
- No retained magnetization after the external field is removed
Why Is Susceptibility Negative in Diamagnetism?
Unlike ferromagnetic or paramagnetic substances that have unpaired electrons contributing to magnetization, diamagnetic substances have all their electrons paired. These paired electrons create tiny looping currents when exposed to a magnetic field, producing an opposing magnetic field that weakly repels the applied force.
Examples of Diamagnetic Substances and Their Susceptibility Values
Different diamagnetic materials exhibit varying degrees of negative magnetic susceptibility (Ï). Below is a table showing some common diamagnetic materials and their susceptibility values:
| Material | Magnetic Susceptibility (Ï) à 10â»â¶ |
|---|---|
| Bismuth | -166 |
| Silver | -19.5 |
| Copper | -9.6 |
| Gold | -3.4 |
| Graphite | -450 |
| Water | -9.0 |
| Mercury | -2.9 |
From this table, bismuth and graphite show the strongest diamagnetic effects.
Measurement of Magnetic Susceptibility (Xâ and Xâ)
Methods to Measure Magnetic Susceptibility
Several techniques are used to measure the susceptibility (Xâ and Xâ) of diamagnetic substances:
- Gouy’s Method
- A sample is placed between the poles of a magnet.
- The change in weight due to magnetic force is measured.
- This helps calculate Ï based on the observed force.
- Faraday’s Method
- Based on the principle that a sample in a non-uniform magnetic field experiences a force.
- Used for materials with weak magnetic responses, like diamagnetic substances.
- SQUID Magnetometer (Superconducting Quantum Interference Device)
- One of the most sensitive methods to measure Xâ and Xâ.
- Can detect extremely small changes in magnetization.
Experimental Demonstration of Diamagnetic Susceptibility
To observe diamagnetic behavior, a simple experiment can be conducted using bismuth or graphite:
- Place a thin sheet of pyrolytic graphite over strong neodymium magnets.
- The graphite will levitate slightly due to its strong diamagnetic properties.
- This demonstrates how Xâ and Xâ influence magnetic response.
This effect is used in scientific research and even in magnetic levitation technology.
Factors Affecting Diamagnetic Susceptibility
Several factors influence the magnetic susceptibility (Xâ and Xâ) of a diamagnetic material:
- Temperature
- Diamagnetic susceptibility is almost independent of temperature.
- Unlike paramagnetic substances, Xâ and Xâ do not change significantly with temperature variations.
- External Magnetic Field Strength
- In weak fields, Xâ and Xâ remain constant.
- In very strong fields, slight nonlinear effects may appear.
- Atomic Structure
- Materials with completely filled electron shells (like noble gases and certain metals) exhibit stronger diamagnetic effects.
Applications of Diamagnetic Susceptibility (Xâ and Xâ)
1. Magnetic Levitation (Maglev Technology)
- Pyrolytic graphite and bismuth can levitate above strong magnets due to diamagnetic repulsion.
- Used in futuristic magnetic transportation systems (Maglev trains).
2. Biomedical Applications
- MRI Scanners rely on the diamagnetic properties of water molecules in human tissues to generate images.
- Blood flow studies use susceptibility differences in oxygenated and deoxygenated blood.
3. Superconductors and Quantum Technology
- Superconductors exhibit perfect diamagnetism, also known as the Meissner effect.
- Research on quantum computing utilizes susceptibility properties for enhanced magnetic control.
4. Shielding Magnetic Fields
- Bismuth is used in scientific instruments to shield delicate components from unwanted magnetic interference.
5. Chemistry and Material Science
- Used in chemical analysis to determine molecular structures and electronic configurations of compounds.
Comparison of Diamagnetic, Paramagnetic, and Ferromagnetic Susceptibility
| Property | Diamagnetic (Ï < 0) | Paramagnetic (Ï > 0) | Ferromagnetic (Ï â« 0) |
|---|---|---|---|
| Interaction with Magnetic Field | Weak repulsion | Weak attraction | Strong attraction |
| Susceptibility Value | Negative | Small positive | Large positive |
| Temperature Effect | Minimal | Inversely proportional | Strong dependence |
| Examples | Bismuth, Copper, Gold | Aluminum, Platinum | Iron, Cobalt, Nickel |
Magnetic susceptibility Xâ and Xâ define how diamagnetic substances respond to external magnetic fields. With a negative susceptibility, these materials experience weak repulsion rather than attraction.
The study of diamagnetic susceptibility is crucial in physics, engineering, medicine, and quantum research. From MRI technology to Maglev transportation, diamagnetism plays a vital role in modern scientific advancements.
Understanding Xâ and Xâ in diamagnetic materials provides deeper insights into electromagnetic behavior and material properties, shaping the future of applied magnetism and technological innovation.