What is Ferromagnetism?
Ferromagnetism or the meaning of ferromagnetism is a mechanism through which certain materials form permanent magnets. With the aid of a strong electrostatic field, these materials can be permanently magnetized. Ferromagnetic metal ions are grouped into small regions called solid-state domains. So every domain is acting like a tiny magnet. The domains of a ferromagnetic unmagnetized piece are randomly oriented so that their magnetic moments are canceled out. When this material is put in a magnetic field, all domains are oriented in the direction of the magnetic field, creating a powerful magnetic effect. Also, when the magnetic field is withdrawn and the ferromagnetic material becomes a permanent magnet, this order of domains remains the same. There are many different forms of magnetism, but ferromagnetism is of the strongest form and is responsible for the widespread occurrence of magnetism in magnets experienced in everyday life.
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Examples of Ferromagnetic Materials
Co (Cobalt)
Fe (Iron)
MnBi
Ni (Nickel)
\[Nd_{2}Fe_{14}B\]
MnSb
\[CrO_{2}\] (Chromium dioxide)
MnAs
Properties of Ferromagnetic Materials
When a rod of this material is placed in a magnetic field, it quickly aligns itself in the field track.
These substances show the permanent magnetism even in the absence of magnetic field
When the substances are heated at high temperatures, the ferromagnetic substances transform to paramagnetic
Permeability of ferromagnetic material is greater than 1.
The mechanism of ferromagnetism is absent in liquids and gases.
The intensity of magnetization (M), relative permeability (\[\mu_{r}\]), magnetic susceptibility (\[\chi_{m}\]), and magnetic flux density (B) of this material will always be positive.
\[X_{m} = \frac{M}{H}\]
\[\mu_r = 1 + X_m\]
B = \[\mu_0\](H + M)
\[\mu_0 \rightarrow\] Magnetic Permittivity of the free space.
H \[\rightarrow\] Applied Magnetic Field Strength.
Hysteresis Loop
The hysteresis loop is formed by altering the magnetizing force while at the same time measuring the material's magnetic flux. When a ferromagnetic material is magnetized in one direction, removal of the imposed magnetizing field will not relax back to zero magnetization. A field in the opposite direction needs to drive it back to zero. When an alternating magnetic field is applied to the object, a loop called a hysteresis loop can be traced for its magnetization.
The absence of magnetization curve re-traceability is the property called hysteresis, which is due to the presence of magnetic domains in the material. Upon reorientation of the magnetic domains, it takes some energy to turn them back.
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This property is useful as a magnetic "memory" of ferromagnetic materials. The magnetic memory aspects of iron make them useful for recording audiotape and for storing data magnetically on computer disks.
Curie Temperature
There is a temperature, over which the ferromagnetic material is paramagnetic. This specific temperature is called temperature Curie. This is, if we rise above Curie temperature, it will cause the ferromagnetic materials to lose their magnetic properties. Curie temperature is represented by \[T_{c}\]. Thermal energy interrupts the magnetic ordering of the dipoles in the ferromagnetic material.
\[E_{thermal} = k_{B} T\]
Curie's law is given by X = \[\frac{C}{T}\]
\[k_{B} \rightarrow\] Boltzmann Constant
C \[\rightarrow\] Curie Constant
Examples,
Fe - 1043 K
Ni - 627 K
Gd - 293 K
Co - 1388 K
What is Antiferromagnetism?
Antiferromagnetic materials are weakly magnetized in the direction of the field, in the presence of a strong magnetic field. This property of the materials is called antiferromagnetism and antiferromagnetic materials are called the materials which exhibit this property. The magnetic moments are aligned in opposite directions in antiferromagnetic materials and are equal in magnitude. Thus, when antiferromagnetic material is unmagnetized the net magnetization is zero due to the exact cancellation of magnetic moments of the adjacent atoms when added in a line.
Application of Ferromagnetic Materials
Ferromagnetic materials have many applications for electrical, magnetic storage, and electromechanical equipment.
Permanent Magnets: Ferromagnetic materials are used for making permanent magnets because its magnetization lasts longer.
Transformer Core: A material used to make the transformer core and choke is subjected to very rapid cyclical changes and the material must also have strong magnetic induction. Ferromagnetic materials are highly used to serve the purpose.
Magnetic Tapes and Memory Store: The magnetization of a magnet is not only dependent on the magnetization field but also on the magnetization cycle it has undergone. Thus, the specimen's magnetization value is a record of the magnetization cycles that it has undergone. Thus, such a machine will serve as a memory storage unit.
Ferromagnetism vs Paramagnetism vs Diamagnetism
Ferromagnetism is a process through which a metal or substance is turned into a highly magnetic substance or a strong permanent magnet when it is subjected to an electromagnetic field. When these substances are brought out of the magnetic field, they remain as strong permanent magnets. This process can only be found in solids and is absent in liquids and gasses. But, when the ferromagnetic substances are exposed to extreme heat, they lose their magnetic property. Paramagnetism is a similar mechanism in which some objects or metals are weakly attracted to magnetic objects. When ferromagnets are subjected to extreme heat, it disrupts the perfectly aligned atoms and changes the object into a paramagnet. On the other hand, diamagnetism is a process in which a substance acts as a weak magnet when the orbital motion of the atoms of the object is changed by an external electromagnetic field. Both the paramagnets and diamagnets are weak magnets and to find the difference between both, the rule of thumb is, an object is said to be paramgent if all the electrons within the objects are unpaired and an object is said to be diamagnetic if all the electrons in the object are paired.
Fun Facts
Magnetar is the most powerful magnet in the universe.
Hammering a magnet can cause its magnetic properties to lose out. Heating up a magnet is another means of destroying its magnetic properties. This is because the molecules lose their alignment north-south and get arranged in random directions.
FAQs on Ferromagnetism Material
1. What is a ferromagnetic material? Please provide some examples.
A ferromagnetic material is a substance that is strongly attracted to an external magnetic field and can be permanently magnetised. This strong magnetism arises from the alignment of microscopic regions called magnetic domains. Even after the external field is removed, these materials can retain their magnetic properties. Common examples include elements like Iron (Fe), Nickel (Ni), Cobalt (Co), and some of their alloys like steel.
2. What are the key properties of ferromagnetic materials as per the Physics syllabus?
Ferromagnetic materials exhibit several distinct properties that are important for the CBSE Class 12 syllabus:
- Strong Attraction: They are strongly drawn into a magnetic field.
- Permanent Magnetism: They can retain their magnetic properties after the external field is removed, a property known as retentivity.
- High Permeability: They have a very high relative magnetic permeability (μr >> 1), meaning they can concentrate magnetic field lines.
- Magnetic Hysteresis: The magnetisation of the material lags behind the applied magnetic field, creating a hysteresis loop.
- Temperature Dependence: They lose their ferromagnetic properties and become paramagnetic above a specific temperature called the Curie temperature.
3. How does the domain theory explain the behavior of ferromagnetic materials?
The domain theory explains that a ferromagnetic material is composed of numerous small regions called magnetic domains. Within each domain, the magnetic moments of all atoms are aligned in the same direction, making each domain a tiny, powerful magnet. In an unmagnetised piece of material, these domains are randomly oriented, so their magnetic effects cancel out. When an external magnetic field is applied, the domains tend to align themselves with the field, resulting in a strong overall magnetisation.
4. What are some important real-world applications of ferromagnetic materials?
The unique properties of ferromagnetic materials make them essential in various technologies:
- Permanent Magnets: Used in electric motors, generators, speakers, and compasses.
- Magnetic Storage: They form the basis of data storage in computer hard drives, magnetic tapes, and credit card strips.
- Transformer Cores: Soft iron, a ferromagnetic material, is used to make cores for transformers and electromagnets to concentrate the magnetic flux and improve efficiency.
- Electromechanical Devices: They are crucial components in relays, sensors, and actuators.
5. How do ferromagnetic materials differ from paramagnetic and diamagnetic materials?
The primary difference lies in their response to an external magnetic field:
- Ferromagnetic materials are strongly attracted to magnetic fields and can become permanently magnetised. Their magnetic susceptibility is large and positive.
- Paramagnetic materials are weakly attracted to magnetic fields. Their magnetism is temporary and disappears once the external field is removed. Their magnetic susceptibility is small and positive.
- Diamagnetic materials are weakly repelled by magnetic fields. This effect is also temporary. Their magnetic susceptibility is small and negative.
This difference in behaviour is due to the arrangement of atomic magnetic moments: aligned in domains for ferromagnets, random but orientable for paramagnets, and induced in opposition for diamagnets.
6. How does temperature affect a ferromagnetic material? Explain the concept of the Curie point.
Temperature significantly impacts the magnetic properties of a ferromagnetic material. As the temperature rises, thermal energy causes the atoms to vibrate more intensely, which disrupts the ordered alignment of the magnetic domains. At a specific critical temperature, known as the Curie temperature (Tc), this disorder becomes so great that the material loses its ferromagnetic properties entirely. Above the Curie point, the material behaves like a paramagnetic substance.
7. What is a hysteresis loop, and why is it a significant concept for ferromagnetic materials?
A hysteresis loop is a graph that illustrates the relationship between the magnetic flux density (B) in a ferromagnetic material and the external magnetising field (H). It shows that the magnetisation of the material lags behind the applied field. The area within the loop represents the energy lost as heat during each magnetisation cycle. This concept is important because the shape of the loop determines a material's application:
- Hard Magnets (Permanent Magnets): Have a wide hysteresis loop, indicating high retentivity and coercivity, making them difficult to demagnetise.
- Soft Magnets (Transformers, Electromagnets): Have a narrow hysteresis loop, indicating low energy loss, making them easy to magnetise and demagnetise.
8. Is steel a ferromagnetic material? If so, why?
Yes, steel is a ferromagnetic material. This is because steel is an alloy that is primarily composed of iron (Fe), which is one of the main ferromagnetic elements. The crystal structure of steel allows the iron atoms to form magnetic domains. The presence and alignment of these domains give steel its strong magnetic properties, allowing it to be used for making both permanent magnets and electromagnets, depending on its specific composition and treatment.
