Magnets can be designated as either: permanent magnets or temporary magnets. Permanent magnets retain their own persistent magnetic field without need for an external magnetic field. Temporary magnets are easily magnetized on exposure to an external magnetic field but lose the magnetism upon removal of the field.
Permanent magnets have an extended lifespan that can range for several decades up to a hundred years even. Contrarily, for temporary magnets their lifespan is dependent on how long they are exposed to an external magnetic field.
Factors Affecting the Life of a Magnet
Various factors influence the lifespan of a magnet which impacts its magnetic strength and overall performance. Some of these factors are discussed below:
Magnetic Material
High-quality materials when used to make magnets tend to retain magnetic properties better over time. Different magnetic materials display varying properties that impact their strength, stability, and resistance to demagnetization.
The quality of a magnetic material will influence magnetic ability in the following ways:
- Coercivity: When you utilize high-quality magnetic materials, they are more resistant to external influences that cause demagnetization.
- Curie Temperature: Higher-quality materials like neodymium alloy portray higher values of Curie temperatures, retaining magnetism at elevated temperatures.
- Hysteresis Losses: You will experience lower hysteresis losses from quality magnetic materials tending to lose less energy during cycles of magnetization and demagnetization.
- Magnetic Strength: High-quality magnetic materials exhibit higher magnetic strengths with the alignment of magnetic domains more effective.
- Remanence: Magnetic materials of higher quality have higher remanence values, retaining larger portions of their magnetization after removal of external field.
- Stability and Longevity: Superior materials are more stable and less prone to demagnetization caused by external factors over time.
Operating Temperature
Magnetic materials display varying sensitivities to temperature changes. As such, as temperature rises, the magnetic properties of a magnet can be significantly affected.
The operating temperature of a magnet will impact magnetic performance as follows:
- Aging: Exposing magnets to high temperatures for an extended period can hasten aging resulting in a gradual loss of magnetic properties.
- Curie Temperature: At this temperature, a ferromagnetic material undergoes a phase transition resulting in permanent loss of magnetization. Exposing a magnet to temperatures close to or above its Curie temperature, induces a significant decrease in magnetic strength or complete demagnetization.
- Demagnetization: Higher temperatures even below a magnet’s Curie temperature, can still affect magnetic performance. Such temperatures can increase the thermal agitation of magnetic domains within the material resulting in temporary reduction in magnetization. While this is reversible, prolonged exposure might lead to a permanent loss of magnetism.
- Magnetic Strength and Coercivity: Magnets generally exhibit a decrease in magnetic strength as temperature rises. Also, the material’s resistance to demagnetization (coercivity) decreases with temperature making a magnet more susceptible to demagnetization at higher temperatures.The quality of a magnetic material will influence magnetic ability in the following ways:
- Coercivity: When you utilize high-quality magnetic materials, they are more resistant to external influences that cause demagnetization.
- Curie Temperature: Higher-quality materials like neodymium alloy portray higher values of Curie temperatures, retaining magnetism at elevated temperatures.
- Hysteresis Losses: You will experience lower hysteresis losses from quality magnetic materials tending to lose less energy during cycles of magnetization and demagnetization.
- Magnetic Strength: High-quality magnetic materials exhibit higher magnetic strengths with the alignment of magnetic domains more effective.
- Remanence: Magnetic materials of higher quality have higher remanence values, retaining larger portions of their magnetization after removal of external field.
- Stability and Longevity: Superior materials are more stable and less prone to demagnetization caused by external factors over time.
Operating Temperature
Magnetic materials display varying sensitivities to temperature changes. As such, as temperature rises, the magnetic properties of a magnet can be significantly affected.
The operating temperature of a magnet will impact magnetic performance as follows:
- Aging: Exposing magnets to high temperatures for an extended period can hasten aging resulting in a gradual loss of magnetic properties.
- Curie Temperature: At this temperature, a ferromagnetic material undergoes a phase transition resulting in permanent loss of magnetization. Exposing a magnet to temperatures close to or above its Curie temperature, induces a significant decrease in magnetic strength or complete demagnetization.
- Demagnetization: Higher temperatures even below a magnet’s Curie temperature, can still affect magnetic performance. Such temperatures can increase the thermal agitation of magnetic domains within the material resulting in temporary reduction in magnetization. While this is reversible, prolonged exposure might lead to a permanent loss of magnetism.
- Magnetic Strength and Coercivity: Magnets generally exhibit a decrease in magnetic strength as temperature rises. Also, the material’s resistance to demagnetization (coercivity) decreases with temperature making a magnet more susceptible to demagnetization at higher temperatures.
These constitute external conditions that can reduce a magnet’s magnetic strength over time or cause it to lose its magnetism entirely. Both permanent and temporary magnets are susceptible to these factors.
Some notable demagnetizing factors include:
- Mechanical Stress and Impact: These cause a shift in the alignment of magnetic domains within a magnet. The result is usually a reduction in magnetic strength or a loss of magnetism.
- Strong External Magnetic Fields: Exposing a magnet to a stronger external magnetic field can weaken or demagnetize the magnet. A stronger external field realigns the magnet’s magnetic domains resulting in an overall reduction in its magnetic strength.
- Temperature: Elevated temperatures disrupt magnetic domains alignment within a magnet with prolonged exposure capable of causing irreversible demagnetization.
- Vibration: Vibrations also induce a shift in the magnetic domains in a magnet which can result in demagnetization over time.
Corrosion and Environmental Conditions
Corrosive environments can deterioration the magnet’s structural integrity affecting performance and longevity. Use of coatings or corrosion resistant materials can help in mitigation.
The dire effects of corrosion and environmental conditions are discussed below:
- Surface Deterioration: Corrosion can form oxides on the magnet surface interfering with its ability to generate a strong and uniform magnetic field. Overall magnetic efficiency is reduced as the surface is consumed by corrosion.
- Reduced Magnetic Field Strength: Corrosion can misalign or disrupt the magnet’s magnetic domains weakening the magnetic field strength. It can also cause non-uniform magnetization across the surface of the magnet.
- Demagnetization: The chemical reactions involved in corrosion can alter the magnet’s internal structure eventually resulting in complete or partial demagnetization.
- Temperature and Humidity: High humidity conditions with fluctuating temperatures accelerate corrosion and ruin the magnet’s internal structure.
- Protective Coatings: Using protective coatings or plating on magnet surfaces can help mitigate the effects of corrosion. Coatings like nickel, zinc, or epoxy can create a barrier between the magnet material and the surrounding environment, preventing direct exposure to corrosive agents.
- Environmental Chemicals: Some chemicals like acids and alkaline solutions accelerate the corrosion process that degrades the magnet’s surface.
Time/Aging
Time has a gradual effect on the magnetic performance of magnets inducing natural decay even under ideal conditions. The effect of time on magnetic performance can be exemplified thus:
- Magnetic Domain Realignment: Over time, the magnetic domains slowly shift inducing a gradual loss in overall alignment and thus magnetic field strength.
- Creep and Relaxation: Repeated thermal expansion and contraction changes a magnet material’s structure inducing creep. This can alter magnetic domain distribution and result in reduced magnetic performance.
- Environmental Effects: Changes like humidity exposure and temperature fluctuations over the life of a magnet can induce degradation and impact magnetic performance.
- Stress: A magnet is subjected to different stress conditions like vibrations and impact which exacerbate the gradual decline in magnetic performance.
A magnet’s shape and design have a significant effect on magnetic field distribution, strength, and susceptibility to demagnetization. Shapes that are complex or more susceptible to mechanical stress have a high likelihood of magnetic decay.
The influence of a magnet’s shape and design on performance is discussed below:
- Magnetic Field Strength: Magnets with larger surface areas (or volume) generate stronger magnetic fields.
- Magnetic Field Distribution: A magnet’s shape and design determine whether the magnetic field will be concentrated or more uniform. This influences the magnet’s interaction with other materials.
- Magnetization Direction: Different shapes necessitates magnetization in various directions, which can impact use for optimal performance.
- Alignment of Magnetic Domains: A well-designed magnet has a higher portion of its magnetic domains aligned in a desired orientation, resulting in superior magnetic performance.
- Demagnetization Risk: Complex shaped magnets have a higher tendency to disrupt their internal magnetic domains making them prone to demagnetization.
Method of Magnetization
The methods of magnetization determine how the magnetic domains within the magnet material align. As a result, they influence magnetic strength, direction, and overall performance.
The influence of magnetization methods on performance is captured below:
- Direction of Magnetization: This is especially useful in applications such as motors where magnetization direction determines operation.
- Uniformity of Magnetization: Certain magnetization methods result in more uniform alignment of magnetic domains enhancing consistency in magnetic field strength.
- Demagnetization Resistance: Properly magnetizing magnets makes them more resistant to external factors capable of weakening or demagnetizing them.
- Strength of Magnetic Field: Magnetization methods determine the alignment of domains which determine the magnet’s field strength.
Radiation Exposure
The type, intensity and duration of exposure of radiation on a magnet material can induce varying effects on magnetic performance. Radiation exposure disrupts domain alignment within a magnet, altering magnetic properties.
A description of the effect of radiation exposure on magnetic performance is summarized thus:
- Disruption of Magnetic Domains: High-energy radiation can interact with a magnet material’s atomic and molecular structure disrupting domain alignment inducing loss of magnetic strength.
- Paramagnetic Effects: Some radiation types can also induce temporary paramagnetic behavior in normally ferromagnetic materials.
- Ionization and Charging: Radiation can induce electron loss or gain in materials by ionizing atoms resulting in localized electric charges affecting magnetic properties.
- Material Degradation: Exposing magnetic materials to radiation can cause structural changes in their crystalline lattice making them defective. Consequently, the magnet’s overall structure is weakened negating performance.
- Temperature Effects: As a material absorbs radiation energy, its temperature can rise and end up disrupting domain alignment affecting magnetism.
The following table shows the susceptibility of magnets to some of the factors that influence lifespan:
|
Magnet |
Susceptibility | Lifespan (Years) | |||
| Max. Operating Temperature | Corrosion | External Fields | Chipping | ||
| Neodymium | 80 to 150°C | High | Low | Medium | 30 + years |
| Alnico | 450°C | Very Low | Medium-High | Medium-High | 20 + years |
| Samarium Cobalt | 250 to 350°C | Low | Very Low | High | 20 + years |
| Ferrite | 250 to 300°C | Very Low | Medium | Medium | 30 + years |
Storage Conditions for a Long Useful Life
Storing magnets in proper conditions is likely to derive effective magnetic performance for a longer period. Ideal storage practices minimize the influence environmental factors have on magnets, such as corrosion, that can lead to demagnetization.
Some ideal conditions for the storage of magnets to maximize usefulness are highlighted below:
- Avoid Mechanical Stress: Carefully handle magnets to avoid stress applications like dropping or bumping. This can disrupt the alignment of magnetic domains weakening the magnets.
- Clean Storage Area: Magnets should be stored in a clean environment without dust and other contaminants which can initiate corrosion.
- Temperature: Store magnets at a temperature within the magnet’s recommended range minimizing fluctuations that can alter domain alignment. The temperature should be below the Curie temperature to prevent unintentional demagnetization. Additionally, avoid temperature extremities (very high or very low) to prevent degradation of magnetic properties and structural deformation.
- Dry Environment: Storing magnets in low humidity levels is vital since moisture accelerates corrosion which negatively hampers magnetic properties over time.
- Non-Magnetic Packaging: When packaging magnets utilize non-magnetic materials like plastic or foam to protect magnets from external magnetic fields.
- Separate Storage: Where you have, multiple magnets, store them separately and with protective spacers. This prevents constant attraction and repelling which could cause surface deterioration.
Conclusion
All magnets will naturally experience some level of degradation in their magnetic properties over their useful life. However, the lifespan can be quite long if a magnet is used within the recommended temperature ranges and protected from demagnetizing factors.
