Understanding the Properties of Diamagnetic, Paramagnetic, and Ferromagnetic Materials

The magnetic properties of materials arise from the behavior of electrons within atoms and their response to external magnetic fields. The three main classes—diamagnetic, paramagnetic, and ferromagnetic materials—differ fundamentally in electron arrangement and magnetic behavior. These differences are essential for understanding magnetism at the JEE Main and Class 12 level.

Fundamental Classification of Magnetic Materials

Materials can be classified as diamagnetic, paramagnetic, or ferromagnetic based on their atomic and electronic structure. This classification reflects how each responds to applied magnetic fields and how magnetic moments develop and align within the material.

Atomic Basis and Magnetic Behavior

Diamagnetic substances contain only paired electrons, resulting in no net permanent magnetic moment. In paramagnetic materials, the presence of some unpaired electrons leads to a small net magnetic moment. Ferromagnetic substances have many unpaired electrons, with atomic magnetic moments aligned in domains, enabling strong magnetization.

Comparison Table: Diamagnetic, Paramagnetic, and Ferromagnetic Materials

Properties of Diamagnetic Materials

Diamagnetic materials exhibit weak repulsion in an external magnetic field. Their susceptibility ($\chi$) is negative and small. The induced magnetic moment always acts opposite to the applied field, due to Lenz’s law. Magnetization does not persist after the external field is removed.

Common diamagnetic examples include copper, bismuth, silver, gold, and lead. In diamagnetic substances, all electrons are paired, resulting in complete cancellation of magnetic moments. For further review of their macroscopic behavior, see the Magnetic Effects of Current and Magnetism page.

Properties of Paramagnetic Materials

Paramagnetic materials are weakly attracted to external magnetic fields. They have a small positive magnetic susceptibility. Magnetization arises from unpaired electrons whose individual moments align slightly with the applied field, but revert to random orientation when the field is removed.

Typical paramagnetic examples are aluminum, platinum, magnesium, and molybdenum. The degree of magnetization decreases as the thermal agitation increases with temperature. The relation between magnetization (M), susceptibility ($\chi$), and applied field (H) is given by $M = \chi H$.

Properties of Ferromagnetic Materials

Ferromagnetic materials show strong attraction toward external magnetic fields. Their susceptibility is large and positive, often thousands of times greater than that of paramagnetic materials. Magnetic domains within ferromagnetics align spontaneously, producing permanent magnetization even after the external field is removed, a phenomenon known as hysteresis.

Examples include iron, cobalt, nickel, and gadolinium. Ferromagnetism disappears above a characteristic Curie temperature, beyond which the substance becomes paramagnetic. For additional information, see Diamagnetic, Paramagnetic, Ferromagnetic Practice Paper for assessment-style JEE questions.

Effect of Temperature on Magnetic Properties

Diamagnetic materials are largely independent of temperature. For paramagnetic materials, elevated temperature increases randomization of moments, reducing magnetization. In ferromagnets, elevated temperature disrupts domain alignment. Above the Curie temperature, ferromagnetic substances transition to a paramagnetic state.

Physical Quantities: Magnetic Susceptibility and Permeability

Magnetic susceptibility ($\chi$) quantifies how a material responds to an applied magnetic field. Relative permeability ($\mu_r$) indicates how easily the field penetrates the substance. These two quantities relate to each other by $\mu_r = 1 + \chi$.

For all diamagnetic materials, $\chi$ is negative and $\mu_r < 1$. For paramagnetic materials, $\chi$ is positive and small; $\mu_r$ is slightly above 1. In ferromagnetic substances, $\chi$ is positive and very large; $\mu_r$ far exceeds 1. These concepts are relevant to many problems in Electromagnetic Induction and Alternating Currents.

Magnetic Domain Structure in Ferromagnetism

The high magnetization in ferromagnetics is explained by the domain theory. Each domain acts as a mini-magnet, with aligned magnetic moments. Application of an external field causes these domains to orient in the direction of the field, resulting in strong overall magnetism. Upon removal of the field, this alignment often persists, giving ferromagnets their permanent magnetic character.

Summary Table: Properties and Examples

Applications of Diamagnetic, Paramagnetic, and Ferromagnetic Substances

Diamagnetic materials are used in magnetic levitation, MRI shielding, and certain quantum physics experiments. Paramagnetic materials function in devices such as oxygen measurement sensors and as MRI contrast agents. Ferromagnetic substances are essential for transformer cores, permanent magnets, electromagnets, and magnetic data storage.

Applications in different fields extend to studying Properties of Solids and Liquids and their microscopic structures.

Key Points for JEE Main Exam Preparation

• Diamagnetic: all electrons paired, small negative susceptibility
• Paramagnetic: some unpaired electrons, small positive susceptibility
• Ferromagnetic: unpaired electrons in domains, large positive susceptibility
• Ferromagnets exhibit hysteresis after magnetizing field removal
• Above Curie temperature, ferromagnets become paramagnetic
• Susceptibility ($\chi$) and permeability ($\mu_r$) are common exam focus points

Equation Summary and Important Relations

The magnetization $M$ is related to the external field $H$ by $M = \chi H$. The magnetic induction $B$ inside a material is given by $B = \mu_0 (H + M)$, where $\mu_0$ is the permeability of free space. For most exam problems, focus on classifying the type and quantitatively evaluating $\chi$ and $\mu_r$.

Further study of related physical principles can be found in Thermal Physics and Basic Properties of Electric Charge for a broader understanding of matter and electromagnetic phenomena.