The Mystery of Magnetism
- Ethan
- Knowledge base
Among the many wonderful phenomena that make up nature, probably one of the most interesting is magnetism. The ancients first found it in the form of natural lodestones. The most familiar magnets in our lives today are the concrete representations of this phenomenon. From the persistence of magnetism, there are three kinds of magnets: temporary magnets, electromagnets, and permanent magnets. In this regard, permanent magnets are the most common in everyday life, while their magnetic force is constant and unchangeable.
According to modern physics, magnetism is a phenomenon originating from the motion of electric charges in materials. When magnetic moments are aligned in an orderly fashion in a material, that material produces a magnetic field, exhibiting familiar attractive or repulsive mechanical characteristics.
What is Magnetism?
Magnetism is a primary physical quality of matter. It describes the behavior of a substance when placed within an external magnetic field and outlines the condition whereby such a substance may be attracted or repelled. The most common feature is the condition of attraction in many ferromagnetic materials, such as iron and cobalt, and nickel.
On a microscopic level, magnetism fundamentally arises from the motion of electrons in atoms. Besides moving around the nucleus of an atom, electrons have their own spin. This gives rise to tiny magnetic moments, which are aligned in various patterns in the different materials that react to applied external magnetic fields, resulting in macroscopic magnetic behavior.
Based on how substances respond to an applied magnetic field, magnetism is mainly classified into the following categories:
Ferromagnetism
Ferrimagnetism
Paramagnetism
Diamagnetism
Altermagnetism
| Type of Magnetism | Typical Examples | Magnetic Strength |
|---|---|---|
| Ferromagnetism | Iron, cobalt, nickel | Strong (permanent magnetism) |
| Ferrimagnetism | Magnetite (Fe₃O₄) | Relatively strong |
| Paramagnetism | Aluminum, oxygen, etc. | Weak |
| Diamagnetism | Water, copper, gold, etc. | Extremely weak (repulsive) |
| Altermagnetism | (Emerging candidate materials) | Varies depending on the material (emerging) |
The History of Magnetism Development
Human beings have been aware of magnetism since ancient times, but the systematic and profound scientific development of magnetism has only occurred in the modern and contemporary stages of physics. The following are significant developments in modern physics and the contributions of scientists, in chronological order, which have formed the basis for contemporary electromagnetism and magnetic materials.
1600: Earth as a Giant Magnet
William Gilbert, an Englishman, was the first to distinguish magnetism from electricity through various experiments. He published De Magnete, in which he said that the Earth itself is a huge magnet and put forward some laws of magnetic poles. His claim earned him the name “father of magnetism.” From here, the history of magnetism entered science in a more systematic manner.
1820: Magnetic Effects of Currents
André-Marie Ampère sets up the theory of magnetic effects of currents. The French physicist André-Marie Ampère quickly followed through proposing Ampère’s law and the current element hypothesis. He quantitatively explained the magnetic interactions of the currents between each other, elaborating on the foundations of classical electrodynamics.
1831: Electromagnetic Induction
Michael Faraday discovers electromagnetic induction. The British scientist Michael Faraday discovered the fact that a magnetic field that varies with time induces current in a closed loop. this culminated in the law of electromagnetic induction. He introduced “lines of force” and built the first prototype of an electric generator, giving birth to an entirely new era in human history, the electrical age.
1864–1873: Unification of Electromagnetism
James Clerk Maxwell unifies electromagnetic theory. The Scottish physicist Sir James Clerk Maxwell proposed what is now called the Maxwell equations: a total unification of electricity, magnetism, and optics. He predicted that electromagnetic waves would travel with the speed of light and demonstrated that light itself was an electromagnetic wave. That was the crowning achievement of classical electromagnetism, an arc of tremendous implications for modern physics.
Mid-20th Century: Complex Magnetic Structures
Louis Néel elucidates complex magnetic structures. The French physicist Louis Néel enunciated the theories of ferrimagnetism and antiferromagnetism, describing cases of well-developed magnetic moments that oscillate in an antiparallel fashion but nevertheless yield a net magnetic moment. This was the theoretical basis of modern magnetic materials such as ferrites.
Visualisation Aids for Magnetic Field Lines
Magnetic field lines are not things you can actually see—they’re abstract mathematical constructs. Generally, auxiliary methods are employed to visualize their shape. one may sprinkle fine iron filings around a magnet. When in the magnetic field, the iron filings become magnetized and thus align along the field lines, making remarkable chain-like patterns.
The pattern relative to a bar magnet reveals curved lines, emanating from the N pole yet thickly clustered. They are very close together near the poles but sparse in the middle and curve to meet at the South Pole. This quite logically illustrates the shape of the magnetic field and dipolar nature.
Macroscopic Manifestation of Earth's Magnetic Field and Its Effects
Earth could be considered a huge spherical magnet, with its magnetic field resembling a tilted dipole, projecting outwards in a dynamic magnetosphere. The most immediate benefits presented by the magnetosphere involve defense: a “force field shield” repels most of the solar wind and high-energy cosmic rays, which would otherwise strip the atmosphere and leave an environment hostile for life, thus allowing it to continue and reduce radiation damage to biological DNA. Nevertheless, some consequences arise: geomagnetic storms disrupt satellite communications and power systems, while plasma instabilities within the magnetotail occasionally cause satellite malfunctions or navigation errors.
How to Measure Magnetism?
Measuring magnetism is a comprehensive field, primarily quantifying magnetic field strength (B or H), magnetic moment, hysteresis curves, and material magnetic property parameters. Depending on the measurement object and application scenario, common instruments and methods vary. In practice, we often select from the following mainstream instruments based on needs. These cover scenarios from daily magnetic field detection to precision material research.
GaussmeterTeslameter
Hysteresis Loop Measurer
VSM
SQUID Magnetometer
| Instrument Name | Main Measurement Parameters | Measurement Principle | Typical Application Scenarios |
|---|---|---|---|
| Gaussmeter/Teslameter | Magnetic field strength (B or H) | Hall effect | Permanent magnet surface field detection, electromagnet air gap measurement, industrial on-site rapid testing and product quality control |
| Hysteresis Loop Measurer (B-H Curve Analyzer) | Hysteresis loop, saturation magnetization, coercivity, remanence | Electromagnetic induction and closed magnetic circuit measurement | Soft/hard magnetic material performance evaluation, magnetic material R&D and batch quality detection |
| Vibrating Sample Magnetometer (VSM) | Magnetic moment, hysteresis loop | Electromagnetic induction (sample micro-vibration) | Magnetic property research on powders, thin films, bulk samples; variable-temperature magnetic testing and laboratory material development |
| Superconducting Quantum Interference Device (SQUID Magnetometer) | Extremely weak magnetic flux/field (10⁻¹⁵ T level) | Superconducting quantum interference effect | Weak magnetic field measurement, biomagnetic signal detection, nanomagnetic materials and cutting-edge physics research |
Which Metals Have Magnetism?
Strong magnetism mainly refers to ferromagnetic and ferrimagnetic metals and alloys.
Ferromagnetic metals: Iron (Fe), Nickel (Ni), Cobalt (Co).
Rare-earth magnetic metals: Gadolinium (Gd), Dysprosium (Dy) exhibit ferromagnetism at low temperatures.
Certain alloys and compounds: Such as NdFeB (Nd₂Fe₁₄B), SmCo (SmCo), magnetite (Fe₃O₄).
Chromium (Cr) and Manganese (Mn), under special conditions, can exhibit magnetism in specific conditions or alloys.
Which Metals Do Not Have Magnetism?
The vast majority of metals exhibit paramagnetism or diamagnetism, showing no strong magnetism macroscopically:
Common non-magnetic metals: Copper (Cu), Aluminum (Al), Gold (Au), Silver (Ag), Zinc (Zn), Lead (Pb), Tin (Sn), Titanium (Ti), Mercury (Hg).
Stainless steel: Austenitic stainless steel is generally non-magnetic.
What Factors Determine the Magnetic Strength of a Magnet?
Material type: The microscopic structure of different materials determines their intrinsic magnetic properties. Intrinsic attributes like Curie temperature and crystal anisotropy directly affect the order and stability of magnetic moments. This is the “innate foundation” of magnet strength, other factors optimise upon it.
Size and shape: Magnets are not isolated. they produce a demagnetising field attempting to weaken internal magnetisation.
Degree of magnetization: Magnets need full magnetization in a strong external field to reach potential. If not saturated, magnetic domains are not fully aligned, resulting in weak macroscopic magnetism. In practice, pulse magnetizers ensure saturation. In the hysteresis loop, remanence Br reflects residual strength after saturation.
Temperature: Rising temperature intensifies atomic thermal vibrations, disrupting magnetic domain order, leading to decreased magnetism. Many permanent magnets have reversible and irreversible losses: magnetism enhances at low temperatures, but exceeds a threshold at high temperatures, causing permanent demagnetization. Selecting high Curie temperature materials improves temperature resistance.
External environment: Strong reverse magnetic fields can flip domains, causing demagnetization. High-energy radiation damages lattices, corrosion erodes surfaces, reducing effective volume. Typically protected by coatings.
Purity and alloy composition: Alloying is key to enhancing magnetism. adding dysprosium to NdFeB increases coercivity, resisting high-temperature demagnetization. High purity reduces defects, improving domain consistency.
Manufacturing and processing techniques: Modern permanent magnets often use powder metallurgy, pulverising alloy powder, orienting and pressing in a magnetic field, sintering for densification, and tempering for optimisation. Orientation makes easy magnetization axes parallel in grains, enhancing anisotropy. heat treatment refines domain walls, increasing coercivity.
Can Magnets Retain Their Magnetic Force Forever?
No, they cannot retain it permanently. Under ideal conditions, modern high-performance permanent magnets have theoretical demagnetization times of hundreds or even thousands of years, but actual lifespan is affected by the environment:
Temperature
External reverse magnetic fied
Mechanical shock and vibration
Time
| Influencing Factor | Demagnetization Cause | Demagnetization Speed |
|---|---|---|
| Temperature | High temperature intensifies atomic thermal motion, disrupting magnetic domain order | Relatively fast; magnetism rapidly disappears completely above Curie temperature (NdFeB ~310°C) |
| External reverse magnetic field | Strong reverse field overcomes material coercivity, flipping or disordering domains | Can occur instantly, especially when reverse field exceeds coercivity, causing immediate substantial weakening or loss |
| Mechanical shock and vibration | Physical impacts cause crystal structure defects or domain wall displacement | Medium speed; gradual significant decay after multiple or intense impacts |
| Time (natural decay) | Slow magnetic relaxation and thermal fluctuations inside the material | Extremely slow; modern high-performance permanent magnets (like NdFeB) typically have annual decay rates under 0.1% at room temperature, lasting decades to centuries |
Some FAQs
Why can magnets attract iron but not copper or aluminium?
The answer lies in the crystal structure. The body-centred cubic structure of ferritic and martensitic stainless steels makes them magnetic, while the face-centred cubic structure of austenitic stainless steels usually makes them non-magnetic.
How to make a magnet retain its magnetism longer?
Avoid exposing the magnet to harsh environments such as high temperatures, strong reverse magnetic fields, severe mechanical impacts, and corrosive substances.
How is Earth's magnetic field generated?
The mainstream theory holds that convective flows of molten iron-nickel in Earth’s outer core, combined with rotation, produce a sustainable magnetic field through a dynamo-like effect.
Can magnetic fields be shielded?
Yes, high-permeability materials can guide magnetic field lines around the shielded area, achieving magnetic shielding.
Conclusion
Magnetism is a physical phenomenon widely present from microscopic particles to the macroscopic universe. It explains many mysteries in nature. Earth’s magnetosphere guides charged particles to excite the atmosphere at the poles, producing spectacular auroras.With the rapid development of spintronics, two-dimensional magnetic materials, and quantum magnetism research, a deeper understanding and applications of magnetism will continue to lead future technological directions.
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