Ferromagnetism and temperature: Does magnetic hysteresis persist at all temperatures in ferromagnetic materials?

Introduction / Context:
Ferromagnetic materials show domain ordering that produces remanence and coercivity — the ingredients of magnetic hysteresis. Temperature strongly influences this ordering through thermal agitation and exchange interactions.

Given Data / Assumptions:

• Ferromagnetic solid with a well-defined Curie temperature T_C.
• Quasi-static magnetization cycles measured below and above T_C.
• No external mechanical stresses or special anisotropy treatments considered.

Concept / Approach:
Below T_C, exchange coupling aligns spins into domains, yielding non-zero remanent magnetization and coercive field — a hysteresis loop appears when cycling H. Above T_C, thermal energy overcomes exchange alignment; the material becomes paramagnetic with zero remanence and negligible coercivity, so the loop collapses to a reversible line through the origin.

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