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What is paramagnetism?

We explain what paramagnetism is, its characteristics, applications and we give several examples. what is paramagnetism

what is paramagnetism? Permanent magnetic
Permanent magnetic moments are randomly oriented, but they align with the applied magnetic field.

What is paramagnetism? what is paramagnetism

The paramagnetism is the attraction experienced by some materials in the presence of an external magnetic field. Paramagnetic substances are weakly attracted to the regions where this field is most intense.

The origin of paramagnetism is the movement of electrons in the atom, since any electric charge in motion behaves like a tiny loop of current, generating its own magnetic field. what is paramagnetism

The magnetism of the electron and the atom is characterized through the vector magnitude called magnetic moment . The atoms of paramagnetic materials have net magnetic moments, since they have unpaired electrons, that is, solitary electrons in one orbital and whose net magnetic moment is not canceled by another. what is paramagnetism

This is what happens in aluminum, a paramagnetic substance whose 3p orbital contains a single electron that gives the atom its net magnetic moment. Iron, on the other hand, whose magnetic response is even more intense, has 4 unpaired electrons at its last level.

When the material is withdrawn from the external field or it disappears, the magnetic moments of a paramagnetic substance return to the initial state of disorder. But while they remain aligned, the substance behaves like a weak magnet.

Characteristics of paramagnetism

Paramagnetic materials are characterized by presenting:

1.- Partially filled outermost electronic layer.

2.- Permanent net magnetic moments, due to the presence of unpaired electrons, whose magnetic moment does not cancel with that of another electron. what is paramagnetism

3.- Randomly oriented magnetic moments in the absence of an external magnetic field.

4.- Net magnetization in the presence of an external field, which disappears as soon as the field is suppressed. It happens that the alignment with the external field favors the state of minimum energy of the electrons. what is paramagnetism

5.- Small positive magnetic susceptibility: between 10 −6 and 10 −2 . Magnetic susceptibility is the dimensionless indicator of the ease of the substance to become magnetized in the presence of an external field. what is paramagnetism

Permanent magnetic

Applications of paramagnetism

Electronic paramagnetic resonance

This technique detects paramagnetic species by applying an external magnetic field to the molecules of a paramagnetic solid, thus inducing certain changes in the spin states, called transitions . what is paramagnetism

By subsequently applying electromagnetic energy in the microwave range, it is possible to produce a particular absorption spectrum, called electron spin resonance .

This spectrum makes it possible to study molecules of organic origin, such as free radicals from the interaction between organic matter and ionizing radiation, offering, among other things, valuable information about the damage that radiation produces in biological tissues.

Inorganic samples can also be analyzed for transition metal ions.

Magnetic cooling what is paramagnetism

A very interesting application of certain paramagnetic salts, such as magnesium nitrate, iron-ammonium sulfate and iron-potassium sulfate, is in the area of ​​low temperatures.

By applying a variable external magnetic field, the temperature of these salts can vary, a phenomenon known as the magnetocaloric effect , first observed in the late 19th century in metallic iron. In this way, temperatures of the order of 0.01 K. what is paramagnetism

Dating samples what is paramagnetism

In this application, the principles of Electronic Paramagnetic Resonance are used to study materials exposed to ionizing radiation. When an object receives ionizing radiation, which can come from radioactive minerals in the earth’s crust, a trace remains, consisting of electrical charges trapped in defects in the material’s crystalline structure. what is paramagnetism

This trace is called the paramagnetic center and it is detectable through Electronic Paramagnetic Resonance techniques.

It is possible to offer a dating of the same knowing that the value of the electric charges in the paramagnetic centers depends both on the time that the sample was exposed to radioactivity and on the dose (energy per unit of mass received).

In this way samples can be dated older than the radiocarbon method allows, for example skeleton teeth from the Quaternary era, which contain radiation sensitive minerals.

Paramagnetic oxygen sensors what is paramagnetism

They are used to detect the amount of oxygen in a sample, since oxygen is paramagnetic, that is, it is attracted by the magnetic field of a magnet. what is paramagnetism

The sensor consists of a magnet that acts as the source of the magnetic field, two spheres filled with nitrogen (a non-paramagnetic material) placed on a rotating bracket between the magnet’s poles, and a mirror in the middle of the bracket.

A beam of light is impinged on the mirror, which is reflected towards some photoelectric cells. Once the oxygen is drawn to the poles of the magnet, a torque is produced that rotates the system of spheres with nitrogen. what is paramagnetism

Thanks to the mirror, this movement is detected by the photoelectric cells, which immediately emit a signal to a system that generates the electrical current necessary to counteract the rotation. This current is proportional to the amount of oxygen present and is easily measured using an ammeter.

Paramagnetic paint for cars

This car paint makes the car change color at the push of a button, thanks to a special polymer that contains a paramagnetic iron oxide. what is paramagnetism

By applying an electric current, the paramagnetic particles align themselves before the field in a certain way, affecting the way the polymer absorbs and reflects light, producing changes in color.

Of course, for the color to change the car must be on. When the engine is off, its base color is usually white.

Examples of paramagnetic materials

The following materials exhibit paramagnetic behavior:

Oxygen (gaseous and liquid)

Oxygen (gaseous and liquid)
Liquid oxygen sticks to the poles of the magnet.

Oxygen is gaseous at room temperature and one of the main components of the atmosphere . A simple experiment in the laboratory shows that liquid oxygen that is poured between the poles of a magnet accumulates there. what is paramagnetism

Cupric sulfate what is paramagnetism

This compound has agricultural applications, as a fungicide, to eliminate pests that affect crops and as an algaecide. A magnet easily attracts a sample of this compound.


Aluminum is a lightweight, strong and inexpensive metal with a multitude of applications. It is part of vehicles, airplanes, household utensils and is widely used in construction. A ball made of aluminum foil is also attracted to a magnet.


Atomic hydrogen is the simplest and most abundant element in the universe, and it is paramagnetic because of the net magnetic moment of its single electron. what is paramagnetism

Austenitic steel

One of the most widely used stainless steels is austenitic stainless steel (which contains austenite, a compound of iron and carbon), with weak paramagnetic properties. what is paramagnetism

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