Ferromagnetic Materials

Last Updated : 16 Jan, 2024

Ferromagnetic Materials are known for their magnetic property like iron and cobalt, can become strong magnets and retain their magnetic properties, finding applications in electronics for data storage and in industrial settings for devices like transformers and magnetic separators.

In this article, we will understand the properties of ferromagnetic materials, their causes, types of ferromagnetic materials, Some ferromagnetic metals and much more related to ferromagnetic materials.

Table of Content

What is Ferromagnetic Material?
Types of Ferromagnetic Materials
List of Ferromagnetic Metals
What is Ferromagnetism?
Comparison with Other Magnetic Materials
Applications of Ferromagnetic Material

What is Ferromagnetic Material?

Ferromagnetic Materials derive their name from “ferrous,” meaning iron, as iron was the first metal recognized for displaying magnetic properties. Ferromagnetism is a distinct magnetic behaviour observed in specific substances like iron, cobalt, alloys, etc. This phenomenon entails these materials gaining permanent magnetism or acquiring attractive capabilities. It involves electrically uncharged materials strongly attracting each other. Ferromagnetism is a property that considers not just the chemical composition but also the microstructure and crystalline structure of a material.

Definition of Ferromagnetic Materials

Ferromagnetic materials, such as iron and cobalt, exhibit a unique magnetic behaviour, attaining permanent magnetism or acquiring strong, attractive powers. This property is not solely determined by chemical composition but also considers the microstructure and crystalline arrangement of the material.

Properties of Ferromagnetic Metals

Following are the properties of ferromagnetic metals:

Magnetic Attraction: Ferromagnetic metals, such as iron, cobalt, and nickel, exhibit strong magnetic properties. They can be attracted to magnets and are capable of becoming magnetized.
Permanent Magnetization: These metals can retain a significant level of magnetization even after exposure to a magnetic field. This property makes them useful in the creation of permanent magnets.
Domain Structure: At the microscopic level, ferromagnetic metals have a domain structure. Domains are small regions where magnetic moments align, contributing to the overall magnetization of the material.
Curie Temperature: Ferromagnetic materials have a critical temperature known as the Curie temperature. Above this temperature, the material loses its ferromagnetic properties.
Saturation Magnetization: Saturation magnetization is the maximum magnetic moment a material can achieve. Ferromagnetic metals can reach high levels of saturation magnetization.
Hysteresis Loop: When subjected to changing magnetic fields, ferromagnetic metals exhibit a hysteresis loop. This loop represents the lag in magnetization response during the magnetic field’s variation.
Applications: Due to their magnetic properties, ferromagnetic metals find applications in various industries, including electronics, telecommunications, and the production of magnetic devices such as transformers and electric motors.
Permanent Dipole Moments: Atoms in ferromagnetic substances have permanent dipole moments arranged in domains.
Alignment with External Field: Atomic dipoles align in the direction of the external magnetic field.
Large Magnetic Dipole Moment: The magnetic dipole moment is significant and aligns with the magnetizing field.
Intense Magnetization: Intensity of magnetization (M) is large and positive, varying linearly with the magnetizing field (H).
Saturation Dependence: Saturation depends on the material’s nature due to the linear relationship between M and H.
High Magnetic Susceptibility: Magnetic susceptibility (X_m = M / H) is large and positive.
Increased Magnetic Flux Density: Magnetic flux density (B = ε₀ (H + M)) is very large and positive inside ferromagnetic materials.
Large Relative Permeability: Relative permeability is significantly large and varies linearly with the magnetizing field.
Attraction to Magnetic Field: Ferromagnetic substances are strongly attracted to magnetic fields and tend to stick to poles in a nonuniform field.
Behavior in Powder Form: In a nonuniform field, ferromagnetic powder accumulates at poles, showing depression in the middle.
Loss of Properties when Liquefied: When ferromagnetic substances are liquefied, they lose their ferromagnetic properties due to higher temperatures.

Types of Ferromagnetic Materials

There are two types of Ferromagnetic Materials

Unmagnetized Ferromagnetic Materials
Magnetized Ferromagnetic Materials

Unmagnetized Ferromagnetic Materials

In unmagnetized ferromagnetic substances, atoms organize into domains, each with a different orientation of magnetic moments. Consequently, the material exhibits no magnetic behavior and is termed unmagnetized.

Magnetized Ferromagnetic Materials

Ferromagnetic materials have tiny regions called domains that can easily align when a small magnetic field is applied. This alignment makes the material much more magnetic than it was originally. The magnetic moments in ferromagnetism run in the same direction as the applied magnetic field when these domains are aligned.

List of Ferromagnetic Metals

The list of ferromagnetic mettals include:

Iron (Fe)
Cobalt (Co)
Nickel (Ni)
Gadolinium (Gd)
Dysprosium (Dy)
Holmium (Ho)
Erbium (Er)
Terbium (Tb)
Neodymium (Nd)
Samarium (Sm)

Cobalt

Cobalt is a metallic element with the symbol Co and atomic number 27. It is a ferromagnetic metal, meaning it exhibits strong magnetic properties. Cobalt is commonly used in the production of magnets, particularly in combination with other elements like aluminum, nickel, and iron. Its magnetic characteristics make it valuable in various applications, including electronics and the manufacturing of magnetic alloys.

Iron

Iron is a well-known ferromagnetic metal. It is a chemical element with the symbol Fe and atomic number 26. Iron is a crucial component in the Earth’s core and plays a significant role in magnetic fields. It is widely used in various industries, from construction to transportation. Iron’s magnetic properties make it indispensable in the production of magnets, electric motors, and other magnetic devices.

Magnetite

Magnetite is not a metal but a naturally occurring mineral and is a form of iron oxide with the chemical formula Fe₃O₄. It is one of the few minerals that is naturally magnetized, making it a ferromagnetic material. Magnetite has been used in compass needles due to its magnetic properties. It is also a key component in the Earth’s magnetic field. In addition to its natural occurrences, magnetite is used in various industrial applications, including the production of heavy media for coal separation and as a pigment in magnetic inks.

What is Ferromagnetism?

Ferromagnetism is a fundamental property of certain materials that allows them to become magnetized in the presence of an external magnetic field and retain this magnetization even after the external field is removed. This property is the basis for most of the magnetic behavior encountered in everyday life.

Read more about Ferromagnetism.

Causes of Ferromagnetism

Ferromagnetism happens when tiny magnets in materials line up together. This alignment makes the material act like a magnet. The main causes are the arrangement of atoms and the way their magnetic moments work together. When these moments align in the same direction, the material becomes strongly magnetic. This alignment is usually influenced by factors like temperature and the material’s structure.

Curie Temperature

Ferromagnetic materials exhibit a special temperature known as the Curie temperature. Below this temperature, these materials tend to be ferromagnetic, meaning they easily form magnets. Above the Curie temperature, their magnetic properties weaken, and they may lose their magnetism.

Magnetic Domains and Orientation

Inside ferromagnetic materials, there are small regions called magnetic domains. Each domain has its magnetic moments (tiny atomic magnets) aligned in a particular direction. In an unmagnetized state, these domains point in random directions, canceling out each other’s magnetic effects.
When an external magnetic field is applied, the domains start aligning in the direction of the field. As the alignment grows, the material becomes magnetized. Even after removing the external field, the magnetic domains tend to stay aligned, making the material act like a permanent magnet.

Comparison with Other Magnetic Materials

The key differences between ferromagnetic, paramagnetic and diamagnetic materials are listed in the following table:

Characteristics	Ferromagnetic Materials	Paramagnetic Materials	Diamagnetic Materials
Response to Magnetic Field	Strongly magnetized	Weakly attracted	Weakly repelled
Retention of Magnetization	Retains magnetization after removal	Does not retain magnetization	Does not retain magnetization
Curie Temperature	Exhibits a distinct Curie temperature	No specific Curie temperature	No specific Curie temperature
Magnetic Domains	Significant role in magnetization	Temporary alignment of moments	N/A (weak magnetic response)

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Ferromagnetic vs Antiferromagnetic vs Ferrimagnetic Material

The key differences between Ferromagnetic, Antiferromagnetic and Ferrimagnetic Material are listed in the following table:

Feature	Ferromagnetic Material	Antiferromagnetic Material	Ferrimagnetic Material
Magnetic Ordering	Atoms align in parallel to each other.	Atoms align in an alternating pattern.	Atoms align in a mixed alignment.
Net Magnetic Moment	Strong net magnetic moment.	Zero or very weak net magnetic moment.	Moderate net magnetic moment.
Magnetic Field Response	Strong attraction to magnetic fields.	Weak response to magnetic fields.	Stronger than antiferromagnetic, weaker than ferromagnetic.
Examples	Iron, Cobalt, Nickel.	Manganese oxide, Iron oxide (as FeO).	Magnetite, Ferrites.
Curie Temperature	High (above room temperature for most materials).	Lower than ferromagnetic materials.	Varies, typically between ferro- and antiferromagnetic ranges.
Magnetic Domains	Present. Domains align in magnetic fields.	Absent or very small.	Present, but with complex domain structures.
Behavior in Magnetic Field	Becomes strongly magnetized.	Shows weak magnetization or none.	Shows magnetization, but less than ferromagnetic.
Applications	Motors, generators, magnetic storage.	Sensors, magnetic resonance imaging (MRI).	Microwave devices, magnetic recording media.

Applications of Ferromagnetic Material

The most common applications of Ferromagnetic Material are:

Electrical Motors and Generators: Ferromagnetic materials are essential in the design of electric motors and generators. They are used in the cores of transformers to enhance the magnetic flux and in the armature of motors to improve the magnetic field interaction.

Magnetic Storage Devices: These materials are used in magnetic storage media like hard disk drives, floppy disks, and magnetic tape. The data is stored in the form of magnetic domains.

Electromagnets: Ferromagnetic materials are used to create powerful electromagnets for various applications like MRI machines, magnetic levitation (maglev) trains, and industrial lifting electromagnets for moving heavy ferromagnetic objects.

Transformers: In transformers, ferromagnetic cores are used to increase the efficiency of the magnetic coupling between the coils.

Inductors and Relays: These materials are used in inductors and relays to enhance the magnetic field and improve the efficiency of these components.

Magnetic Sensors: They are used in various types of magnetic sensors, such as Hall effect sensors, to detect and measure magnetic fields.

Loudspeakers and Microphones: Ferromagnetic materials are used in the voice coils of loudspeakers and microphones to convert electrical signals into mechanical vibrations, and vice versa.

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