This document discusses different types of magnetism exhibited by solids, including antiferromagnetism, ferrimagnetism, and how temperature affects magnetic behavior. It defines antiferromagnetism as opposite alignment of magnetic ions that results in no net magnetism. Ferrimagnetism occurs when magnetic moments are opposed but unequal, leaving a spontaneous magnetization. The document also explains that increasing temperature causes thermal vibrations that randomize atomic magnetic moments, decreasing saturation magnetization and destroying magnetic order at the Curie or Néel temperature, above which materials become paramagnetic.

1. Machine Design & Equipment
Training
Lecture No. 8
Anti-ferromagnetism,
ferrimagnetism and Effect of
temperature
6th Term B.E (Electrical)
Engr. Fida Hussain

2. Antiferromagnetism
• Type of magnetism in solids such as manganese
oxide (MnO) in which adjacent ions that behave as
tiny magnets (in this case manganese ions, Mn2+)
spontaneously align themselves at relatively low
temperatures into opposite, or antiparallel,
arrangements throughout the material so that it
exhibits almost no gross external magnetism.

3. • In antiferromagnetic materials, which include certain
metals and alloys in addition to some ionic solids, the
magnetism from magnetic atoms or ions oriented in one
direction is canceled out by the set of magnetic atoms
ions that are aligned in the reverse direction.
• The magnetic susceptibility of an antiferromagnetic
material typically shows a maximum at the Néel
temperature.

4. • This spontaneous antiparallel coupling of atomic
magnets is disrupted by heating and disappears
entirely above a certain temperature, called the Néel
temperature.
• Antiferromagnetic solids exhibit special behaviour in
an applied magnetic field depending upon the
temperature.
• At very low temperatures, the solid exhibits no
response to the external field, because the antiparallel
ordering of atomic magnets is rigidly maintained. At
higher temperatures, some atoms break free of the
orderly arrangement and align with the external field.

5. Ferrimagnetism
• Type of permanent magnetism that occurs in solids in
which the magnetic fields associated with individual
atoms spontaneously align themselves, some parallel,
or in the same direction (as in ferromagnetism), and
others generally antiparallel, or paired off in opposite
directions (as in antiferromagnetism).
• A ferrimagnetic material is one in which
the magnetic moments of the atoms on
different sublattices are opposed, as
in antiferromagnetism; however, in ferrimagnetic
materials, the opposing moments are unequal and a
spontaneous magnetization remains.

6. • Ferrimagnetic materials ar like ferromagnets in that they
hold a spontaneous magnetization below the curie
temperature, and show no magnetic order above this
temperature.
• Ferrimagnetism occurs chiefly in magnetic oxides known
as ferrites.

7. The Influence Of Temperature
On Magnetic Behavior
• Temperature can also influence the magnetic
characteristics of materials.
• Recall that raising the temperature of a solid results in an
increase in the magnitude of the thermal vibrations of
atoms.
• The atomic magnetic moments are free to rotate; hence,
with rising temperature, the increased thermal motion of
the atoms tends to randomize the directions of any
moments that may be aligned.

8. • For ferromagnetic, antiferromagnetic, and ferrimagnetic
materials, the atomic thermal motions counteract the
coupling forces between the adjacent atomic dipole
moments, causing some dipole misalignment, regardless
of whether an external field is present.
• This results in a decrease in the saturation magnetization
for both ferro-and ferrimagnets.
• The saturation magnetization is a maximum at 0 K, at
which tem-perature the thermal vibrations are a
minimum.With increasing temperature, the saturation
magnetization diminishes gradually and then abruptly
drops to zero at what is called the “Curie temperature TC”

9. • At TC curie temperature the mutual spin coupling
forces are completely destroyed, such that for
temperatures above TC both ferro-magnetic and
ferrimagnetic materials are paramagnetic.
• The magnitude of the Curie temperature varies from
material to material.
• Antiferromagnetism is also affected by temperature;
this behavior vanishes at what is called the Néel
temperature. At temperatures above this point,
antiferromagnetic materials also become
paramagnetic.