A fundamental magnetic phenomenon where certain materials exhibit strong magnetic properties and can become permanent magnets due to aligned magnetic moments of their atoms.

Ferromagnetism

Ferromagnetism represents one of the most powerful and widely observed forms of magnetism, characterized by materials that can exhibit strong, persistent magnetic properties even in the absence of an external magnetic field.

Fundamental Mechanism

At its core, ferromagnetism emerges from the quantum mechanical property of electron spin. Within ferromagnetic materials, unpaired electrons in atomic orbitals create tiny magnetic moments. Through a phenomenon known as exchange interaction, these magnetic moments tend to align parallel to each other within regions called magnetic domains.

Key Properties

Spontaneous Magnetization

Occurs below the Curie temperature
Results in net magnetic moment even without external fields
Driven by quantum mechanical exchange energy

Magnetic Hysteresis

Ferromagnetic materials display a distinctive behavior called hysteresis, characterized by:

Remanent magnetization after field removal
Coercivity requiring reverse field for demagnetization
magnetic saturation at high field strengths

Common Ferromagnetic Materials

Pure Elements:
- Iron
- Nickel
- Cobalt
Alloys and Compounds:
- Steel
- Permalloy
- Various rare-earth magnets

Applications

Ferromagnetism's unique properties enable numerous technological applications:

Temperature Dependence

The strength of ferromagnetic ordering depends critically on temperature:

Below Curie temperature:
- Magnetic moments maintain alignment
- Strong magnetic properties present
Above Curie temperature:
- Thermal energy overcomes exchange interaction
- Material becomes paramagnetic

Modern Research Directions

Current research focuses on:

The understanding and manipulation of ferromagnetic properties continues to drive innovations in technology and fundamental physics research.