Paramagnetism

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:

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

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:

Property	Paramagnetism	Diamagnetism
Nature of Materials	Paramagnetic materials are those that have unpaired electrons in their atoms or ions.	Diamagnetic materials are those that have all paired electrons in their atoms or ions.
Magnetic Moment	Paramagnetic materials have a nonzero magnetic moment due to the presence of unpaired electrons.	Diamagnetic materials have a very weak, negative magnetic moment, induced by an external magnetic field.
Interaction with External Magnetic Field	Paramagnetic materials are attracted to an external magnetic field and tend to align their magnetic moments with the field.	Diamagnetic materials are weakly repelled by an external magnetic field, causing them to create a very small opposing magnetic field.
Susceptibility	Paramagnetic materials have positive magnetic susceptibility.	Diamagnetic materials have negative magnetic susceptibility.
Temperature Dependence	Paramagnetism decreases with decreasing temperature and may become negligible at very low temperatures.	Diamagnetism is a universal property of all materials and does not depend significantly on temperature.
Examples	Examples of paramagnetic materials include iron, nickel, and oxygen.	Examples of diamagnetic materials include bismuth, copper, and graphite.

Paramagnetism, Diamagnetism and Ferromagnetism

Paramagnetism, Diamagnetism and Ferromagnetism are three property exhibited by magnetic materials. A detailed

Property	Paramagnetism	Diamagnetism	Ferromagnetism
Nature of Attraction	Weak attraction towards magnetic field	Weak repulsion by a magnetic field	Strong attraction and alignment with magnetic field
Origin of Magnetism	Unpaired electrons in atoms or ions	No unpaired electrons; induced by an external magnetic field	Permanent magnetic moments due to alignment of electron spins
Magnetic Susceptibility	Positive (χ > 0)	Negative (χ < 0)	Very high positive (χ >>> 0) for some materials
Temperature Dependence	Decreases with increasing temperature	Decreases with decreasing temperature	Strongly dependent on temperature; may exhibit Curie temperature
Examples	Iron, aluminum, platinum	Bismuth, copper, graphite	Iron, cobalt, nickel, gadolinium

Applications of Paramagnetism

Paramagnetic substances, like gadolinium-based contrast agents, enhance the visibility of certain tissues in MRI scans, aiding in the diagnosis of medical conditions.

Paramagnetic materials play a role in catalysis, facilitating chemical reactions by providing a surface for reactions to occur. This is particularly useful in industrial processes.

Paramagnetic materials are utilized in the construction of various electronic devices, such as sensors and transistors, due to their magnetic properties.

Paramagnetism is employed in laboratories for research purposes, helping scientists analyze materials and understand their magnetic behavior, which can provide insights into their properties.

Paramagnetic ions can be used in chemical analysis and separation techniques, aiding in the purification of certain substances.

Paramagnetic materials are used in sensors for environmental monitoring, helping detect and measure certain gases and pollutants.

Paramagnetic materials are employed in measuring magnetic susceptibility, a property used to understand the response of materials to an applied magnetic field.

Paramagnetic ions can influence the NMR spectra, providing valuable information in chemical analysis and structural studies.

Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI) in paramagnetism involves exploiting the magnetic properties of certain substances. Paramagnetic materials contain unpaired electrons, causing them to exhibit a weak magnetic moment when exposed to a magnetic field. In MRI, contrast agents with paramagnetic properties are administered to enhance image quality. These agents temporarily alter the local magnetic field, improving visibility of tissues and structures during imaging. By manipulating the magnetic properties of paramagnetic substances, MRI provides detailed, high-resolution images of internal body structures, aiding in medical diagnosis and treatment planning.

Paramagnetism in Everyday Life

Paramagnetism is a property found in certain materials where individual atoms or molecules have magnetic moments that align with an external magnetic field. In everyday life, some common examples include aluminum, platinum, and oxygen. When exposed to a magnetic field, these materials become weakly attracted to it. While the effect is subtle, it has practical applications, such as in magnetic resonance imaging (MRI) machines used in medical diagnostics and certain electronic components like transformers.

Paramagnetism Frequently Asked Questions

What is the Meaning of Paramagnetism?

Paramagnetism is a weak attraction to magnetic fields. Paramagnetic materials align with the field but exhibit low magnetization.

How Do Paramagnetic Materials Behave in Magnetic Fields?

In magnetic fields, paramagnetic materials align weakly with the field, displaying temporary magnetism.

What Are Some Examples of Paramagnetic Elements?

Examples of paramagnetic elements include aluminum, platinum, and chromium.

Can Paramagnetic Materials Become Ferromagnetic?

Paramagnetic materials can become ferromagnetic under certain conditions, exhibiting stronger and persistent magnetization.