Magnetic remanence is a measure of the ability of a material to retain its magnetization after an external magnetic field is removed. It is an essential property of materials used in the construction of magnets and various applications of magnetism, such as in magnetic storage devices and electric motors.
The magnitude of magnetic remanence is typically measured in units of magnetic flux density, also known as magnetic field strength or magnetization. The magnetic flux density is related to the number of magnetic field lines per unit area and is typically measured in units of tesla (T).
Main Types Of Magnetic Remanence
There are two main types of magnetic remanence: hysteresis remanence and saturation remanence.
Hysteresis remanence, also known as residual magnetization or remanence, is the magnetization of a material after an external magnetic field is removed, but only when the material has been previously magnetized through a process of hysteresis. This type of remanence is important in the design of permanent magnets, as it determines the maximum magnetization that can be achieved in the material.
On the other hand, saturation remanence is the magnetization of a material when it is fully saturated with an external magnetic field. This remanence is important in the design of electromagnets and in the optimization of magnetic storage devices, as it determines the maximum amount of data that can be stored on a given material.
What Factors Affect Magnetic Remanence?
Several factors can affect the magnetic remanence of material, including:
- Temperature: The magnetic remanence of material generally decreases with increasing temperature due to the increased thermal motion of the magnetic moments.
- Crystalline structure: The magnetic remanence of a material can be affected by the arrangement of the atoms within the crystal lattice. For example, materials with a face-centered cubic (FCC) structure tend to have higher remanence than those with a body-centered cubic (BCC) structure.
- External magnetic field: The magnetic remanence of a material can be affected by the strength and orientation of an external magnetic field.
- Presence of impurities: The presence of impurities or defects in a material can affect its magnetic properties, including its remanence.
- Magnetization history: The magnetic remanence of a material can be affected by its magnetization history, including the number and strength of the magnetic fields it has been subjected to.
- Size and shape of the sample: The magnetic properties of a material can depend on the size and shape of the sample, particularly in the case of thin films or nanostructures.
- Composition: The chemical composition of a material can affect its magnetic properties, including its remanence.
- Doping: The magnetic properties of a material can be affected by the introduction of dopants, which are impurities that are intentionally added to alter their electrical and/or magnetic properties.
How To Measure Magnetic Remanence?
Several techniques can be used to measure the magnetic remanence of a material.
- Vibrating Sample Magnetometer (VSM): This is a common technique for measuring the magnetization of a material. It involves applying an oscillating magnetic field to the sample and measuring the resulting oscillating voltage in a pickup coil. The amplitude and phase of the oscillating voltage are used to calculate the sample’s magnetization.
- Hysteresis Loop Measurements: This method involves applying a varying magnetic field to the sample and measuring the magnetization as a function of the applied field. The result is a hysteresis loop, which provides information about the material’s magnetic remanence and other magnetic properties.
- SQUID (Superconducting Quantum Interference Device): This highly sensitive device can measure small changes in magnetic fields. It is often used to measure the magnetization of very small samples or samples with low magnetic moments.
- Magneto-Optical Kerr Effect (MOKE): This method involves measuring the change in the polarization of light reflected off a sample as the applied magnetic field varies. It can be used to measure the magnetization of thin films and other samples that are transparent to visible light.
The Unit Of Magnetic Remanence
The unit of magnetic remanence is the tesla (T), the standard unit of magnetic field strength in the International System of Units (SI). It is defined as the field strength required to produce a force of one newton per ampere of current per meter of the conductor in a vacuum.
Magnetic remanence is typically measured in terms of the residual magnetization of a material, which is the magnetic field strength remaining in the material after an external magnetic field has been removed. This is often expressed in the residual magnetization per unit volume or the mass-specific residual magnetization. These quantities are typically expressed in units of tesla (T) or in units of gauss (G), which is a unit of magnetic field strength equal to 0.0001 teslas.
For example, a material with a mass-specific residual magnetization of 10 kG (kilogauss) would have a residual magnetization of 0.01 tesla per gram of material. This is often written as Br = 0.01 T/g, where Br is the symbol for magnetic remanence.
Significance Of Magnetic Remanence
Magnetic remanence is essential in various applications because it determines the ability of a material to retain its magnetization after an external magnetic field has been removed. Materials with high magnetic remanence are often used in permanent magnets, which generate strong magnetic fields in various applications, including motors, generators, and sensors.
In addition, the magnetic remanence of a material can influence its behavior in the presence of external magnetic fields. For example, materials with high magnetic remanence may be more susceptible to magnetic interference or more difficult to demagnetize. This can be important in applications where precise magnetic field control is required, such as in magnetic resonance imaging (MRI) or in the manufacturing of electronic devices.
Conclusion
Magnetic remanence is an essential property of magnetic materials that determines their ability to retain and generate magnetic fields. It is an important consideration in the design and use of magnetic devices and systems.