Paramagnetism is a property where certain materials are weakly attracted to magnetic fields, exhibiting temporary alignment of magnetic moments. This article explores paramagnetism, a property where certain materials weakly respond to magnetic fields. It covers the basics, differences with diamagnetism, factors influencing paramagnetism, and everyday applications like MRI.

What is Paramagnetism?

Paramagnetism is a property of material by virtue of which, when a material is placed in a magnetic field, it gets weakly magnetized. The materials which exhibit paramagnetism are called Paramagnetic Materials. In such substances, the individual atoms or molecules have unpaired electrons, causing them to align with the external magnetic field. This alignment enhances the overall magnetic moment of the material, making it weakly attracted to the applied magnetic field. Unlike ferromagnetic materials, which retain their magnetization even after the field is removed, paramagnetic materials only exhibit magnetism in the presence of an external magnetic field. Common paramagnetic substances include oxygen and some metal ions. The magnetic response is relatively weak, and paramagnetism is often observed at room temperature.

Paramagnetism Definition

Paramagnetism is a property exhibited by certain materials which in the presence of an external magnetic field develop a temporary magnetic moment, aligning their magnetic dipoles with the field.

Paramagnetic Materials

Paramagnetic materials are those which exhibits the property of paramagnetism. The examples of paramagnetic materials include Aluminum, lithium, molybdenum, magnesium etc. The magnetic susceptibility of paramagnetic materials is less than one and greater than zero.

Magnetic Moments in Paramagnetic Materials

Magnetic moments in materials occur due to the existence of unpaired electrons. In paramagnetic materials, the magnetic moments of individual atoms or ions do not align spontaneously in the absence of an external magnetic field. However, when an external magnetic field is applied, the magnetic moments tend to align with the field direction, leading to a net magnetization of the material.

Magnetic moments in paramagnetic materials can be described by the Langevin function, which relates the magnetic susceptibility (χ) of the material to the applied magnetic field (B) and temperature (T). The Langevin function is given by:

[Tex]M = \frac{N \cdot \mu^2 \cdot B}{3 \cdot k \cdot T} \cdot L(x)[/Tex]

where,

• M is the magnetization of the material,
• N is the number of magnetic moments per unit volume,
• μ is the magnetic moment of each magnetic moment,
• k is Boltzmann’s constant,
• T is the temperature in kelvin,
• L(x) is the Langevin function, which depends on the dimensionless parameter [Tex] x = \frac{\mu \cdot B}{k \cdot T}[/Tex]

Curie Law

Curie law of paramagnetism describes the magnetic susceptibility (χ) of a paramagnetic material as a function of temperature (T). It was formulated by Pierre Curie in the 19th century and is expressed mathematically as:

χ = C/T

where,

• M is Magnetization
• χ is Magnetic Susceptibility
• C is Material-specific Curie Constant
• T is Absolute (Kelvin) Temperature

According to the Curie law, the magnetic susceptibility of a paramagnetic material is inversely proportional to its absolute temperature. Curie law holds true for paramagnetic materials in the absence of external magnetic fields. It describes the behavior of paramagnetic materials above their Curie temperature, which is the temperature at which they undergo a phase transition from a paramagnetic to a non-magnetic state.

Factors Influencing Paramagnetism

Paramagnetism is a property exhibited by certain materials where they are attracted to an external magnetic field. Several factors influence the paramagnetic behavior of a substance:

Unpaired Electrons: Paramagnetism is related to the presence of unpaired electrons in the atoms of a material. Elements with unpaired electrons have magnetic moments, which align with an external magnetic field, causing the material to be attracted to it.

Incompletely Filled Orbitals: Elements with incomplete electron shells or orbitals are more likely to exhibit paramagnetism as they are prone to having unpaired electrons.

Magnetic Moment: The magnetic moments of individual atoms in a material contribute to its overall magnetic behavior. If these moments are not canceled out by opposing moments, the material is more likely to display paramagnetism.

Temperature: The temperature of a material can influence its paramagnetic properties. Generally, as the temperature increases, thermal motion disrupts the alignment of magnetic moments, reducing the overall paramagnetic effect.

D orbital Electrons: Transition metals and their compounds are often paramagnetic due to the availability of unpaired d electrons. The presence of these transition metals in a material can enhance its paramagnetic characteristics.

Strength of Magnetic Field: The strength of the external magnetic field applied to a material directly affects its paramagnetic response. A stronger magnetic field will result in a more pronounced paramagnetic effect.

Molecular Composition: The specific atoms and their arrangement in a material impact its magnetic behavior. Some materials inherently possess a higher degree of paramagnetism based on their elemental composition.

Paramagnetism vs Diamagnetism

The difference between paramagnetism and diamagnetism is tabulated below: