Magnetic materials – defining temperature for antiferromagnetism The temperature below which a material exhibits antiferromagnetic ordering and above which it becomes paramagnetic is called:

Introduction / Context:
Magnetic ordering in solids depends strongly on temperature. Different magnetic materials lose their ordered spin arrangements at characteristic temperatures due to thermal agitation. Identifying the correct term for antiferromagnets is essential in solid-state physics and materials engineering.

Given Data / Assumptions:

• Material of interest exhibits antiparallel spin alignment at low temperature (antiferromagnetism).
• Upon heating, long-range order disappears and the material becomes paramagnetic.
• No external magnetic field is required to define the transition temperature.

Concept / Approach:

The critical temperature where antiferromagnetic long-range order collapses is called the Néel temperature (T_N), named after Louis Néel. For ferromagnets, the analogous critical temperature is the Curie temperature (T_C). The Weiss temperature is a parameter from mean-field theory often used in Curie–Weiss law fits but is not the universal name of the transition itself. Blocking temperature applies to superparamagnetism in nanoparticles and is not the same as the antiferromagnetic transition temperature.

Step-by-Step Solution:

Verification / Alternative check:

Textbook phase diagrams and susceptibility curves show a cusp or change in slope at T_N for antiferromagnets, consistent with the definition used here.

Why Other Options Are Wrong:

Weiss temperature is a theoretical parameter. Curie temperature applies to ferromagnets. Blocking temperature concerns superparamagnetic relaxation in small particles rather than bulk antiferromagnetic order.

Common Pitfalls:

Confusing Curie and Néel temperatures, or assuming all magnetic transitions share the same terminology.

Final Answer:

Néel temperature