Ferromagnetic Materials

Ferromagnetic Materials - A Complete Guide

There are three different types of magnetism displayed by various metals. They include ferromagnetism, diamagnetism and paramagnetism. Ferromagnetic materials are characterized by their superior properties that make magnetizing them fairly easy.

What is a Ferromagnetic Material?

These are a select group of metals that possess the ability to become permanent magnets owing to their unique magnetic properties. They have a relatively high susceptibility to magnetic fields which allows them to be easily magnetized. This type of magnetism is displayed by a category of metals referred to as ferrous metals, Iron, cobalt, and nickel are examples of such kinds of metal.

These materials contain unpaired electrons as well as atomic dipoles. These properties alongside their crystalline structure increase their magnetic susceptibility and their ability to instantly become magnetic.

Types of Ferromagnetic Metals and Alloys

Several materials display this property. These materials include;

Iron
Iron

This metal has a crystalline structure with two unpaired electrons in outer shells. The α variation of the metal is ferromagnetic. The metal’s Curie point is 1043°K beyond which it loses its superior properties. It has domains within which its unpaired electrons spin to create the magnetic field as they align. Prolonged exposure will result in the magnetic saturation of the metal. It is also very susceptible to external magnetic fields which allow it to be easily magnetized.

Cobalt
Cobalt

It has a relatively high magnetic saturation which increases its ability to be permanently magnetized. Just like iron, it can maintain its properties until it hits Curie point which is 1145°C. Its magnetic properties are influenced by the size of its particles and may differ with varying sizes. It exhibits magnetic anisotropy which is characterized by the alignment of the electron in a similar direction. The metal can be temporarily demagnetized using a stronger magnet. It also has a strong magnetic permeability.

Nickel
Nickel

Nickel is another ferromagnetic material that exhibits that displays paramagnetism in its pure state. However, if it contains a trace of iron or cobalt it becomes ferromagnetic with a high magnetic susceptibility. Its ferromagnetic ability largely depends on other elements found in it. It loses all its ferromagnetic abilities at 355°C.

Dysprosium
Dysprosium

This is a material with a high susceptibility to magnetic influence and can therefore be easily magnetized. Its magnetic properties are influenced by temperature and display ferromagnetic properties below 85°K. In its basal plane, it experiences spontaneous magnetization as well as an increase in temperature in the presence of a magnetic field.

Terbium
Terbium

Terbium is a rare-earth element that is paramagnetic at room temperatures but displays ferromagnetic properties below 237°K. Once introduced to a magnetic field its temperature begins to rise.

Neodymium
Neodymium

This material is typically fused with materials such as boron and iron which greatly enhance its magnetic properties although in its natural state, it is anti-ferromagnetic. It is magnetized along a particular crystal axis because of its elevated uniaxial anisotropy. Its microstructure and crystalline structure are some of the properties that make it an exceptionally strong magnet.

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Soft Ferromagnetic Material vs Hard Ferromagnetic Material

There are two main categorizations of ferromagnetic materials; soft and hard ferromagnetic materials. Their categorizations are influenced by different properties including retention capacity, permeability, and coercivity. Another factor that determines the category is the curves of their hysteresis.

Soft ferromagnetic require only a limited external magnetic influence to demagnetize them hence they have a low coercivity. They release limited energy in the loop making their hysteresis curve narrow and steep. They also have a reduced retention capacity and permeability.

On the other hand, hard ferromagnetic materials have a higher magnetic strength with increased coercivity. It takes a stronger magnetic field to demagnetize it which allows it to have a higher retention ability. Their curve is wide as it releases a lot of energy in the hysteresis loop.

Soft Ferromagnetic Material vs Hard Ferromagnetic Material
Practical Applications of Ferromagnetic Materials

Practical Applications of Ferromagnetic Materials

Owing to their magnetic abilities ferromagnetic materials have a multitude of uses. These applications include the production of the following;

  • Permanent magnets
  • Transformer cores
  • Magnetic storage devices
  • Electrical and electromechanical equipment
  • Electromagnets

Different types of ferromagnetic materials are suitable for various uses. Ferromagnetic materials are highly suitable for applications that depend on magnetic properties. With their different properties, it is important to select a ferromagnetic material that will meet all your requirements.

Causes of Ferromagnetism

Ferromagnetism is caused by the following factors:

Atomic Dipoles

This refers to the detachments of positive and negative charges in a molecule. There are sections in materials that display ferromagnetism called domains in which the alignment of these atomic dipoles occurs. This alignment results in the creation of a net magnetic moment which is nil in these materials as it occurs in an opposing direction.

Crystal Structure

The crystal structure greatly impacts the orientation of the atomic dipoles and other magnetic features of ferromagnetic materials. The structure can facilitate the spinning of the dipoles or can act as a hindrance preventing the creation of a magnetic moment. It also influences properties such as domain structure, magnetic ordering, space groups, anisotropy, and Curie temperature.

Quantum Mechanical Effects

The electrons in ferromagnetic materials are controlled by quantum mechanics. The Pauli exclusion principle dictates the orientation of the electrons stating that when close electrons cannot align themselves in a similar direction. This makes them anti-parallel which results in a strong repulsion that causes the alignment of electrons to spins

Hysteresis

This refers to the lagging and alignment of domains when a material is exposed to magnetic fields from an external influence which causes increased magnetization. This phenomenon influences other magnetic properties such as saturation, coercivity, and susceptibility. The degree of hysteresis is influenced by the strength of the external magnetic field.

Properties of Ferromagnetic Materials

The properties of ferromagnetic materials include

  • These materials have a microscale arrangement of electron spins which creates magnetic domains that intensify the magnetic field of the materials.
  • In their domain, these materials have a permanent dipole moment that is aligned in a uniform direction similar to the external field.
  • These materials’ magnetism is terminated when the material is exposed to temperatures above their Curie point. This is caused by the disappearance of their long-range order caused by these temperatures.
  • The materials have elevated levels of magnetic susceptibility allowing them to be easily magnetized and display increased magnetic properties.
  • When an external field is applied to these materials strength in terms of its magnetic ability will continue to grow until its maximum limit. This limit can also be termed as its saturation level.
  • Their magnetic abilities can be graphically depicted as a form of applied magnetic field. This graph is referred to as a hysteresis loop and allows to tracking of magnetized, demagnetized, and re-magnetized materials.
Curie Temperature for Ferromagnetic Metals

Ferromagnetic materials go through a change known as phase transition when exposed to temperatures that are above their curie temperature. Temperatures above the material limit will result in the loss of the material’s ability to magnetize. The resulting material will only exhibit para-magnetic properties.

The Curie temperature of ferromagnetic materials includes;

  • Iron: 770 °C
  • Nickel: 360 °C
  • Cobalt: 1121 °C
Comparing Ferromagnetism to other Magnetic Materials

· Ferromagnetic vs Diamagnetic Materials

Ferromagnetic materials feature a heightened pull when exposed to magnetic fields which is a result of the spinning unpaired electrons as they fall in line toward an external field. On the opposite side of the scales are diamagnetic materials that have no such electrons. Because of this these materials experience an induced form of magnetic moments leading to a repulsive effect.

Diamagnetic materials can therefore be characterized by their ability to generate a repulsive movement regardless of the pole they are exposed to. Ferromagnetic materials will similarly be pulled towards a field regardless of the orientation of the pole.

· Ferromagnetic vs Paramagnetic Materials

Paramagnetic materials are materials that display a muted attraction favoring only one pole owing to the presence of unpaired electrons in their structure. It also has a permanent dipole moment that is formed as a result of the incomplete cancelation of electron spin. When exposed to an external field any property displayed due to proximity with the field is lost

On the other hand, ferromagnetic materials that have both a permanent dipole moment and unpaired electrons experience an attraction to both poles. They have magnetic domains which amplify their magnetic strength. They hold onto their magnetic properties even in the absence of external influence.

· Ferromagnetic vsAntiferromagnetic Material

The magnetic moments of antiferromagnetic materials involve atoms that align in an antiparallel formation when near each other, leading to the reversal of their magnetic properties. Antiferromagnetic materials contain a reduced magnetic dipole moment that aligns in the direction opposite to the magnetizing field. On the other hand, ferromagnetic materials contained increased large magnetic dipole moment facing a similar direction of the magnetizing field.

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