Question

what are unidirectional magnetic moments? and what is the principle behind them.

Answer 1

Magnetic anisotropy describes how an object's magnetic p​​​​​​roperties can be different depending on direction. In the simplest case, their is no preferential direction for an object's magnetic moment. It will respond to an applied magnetic field in the same way regardless of which direction the field is applied. This is known as magnetic isotropy.

Magnetically anisotropic materials will be easier or harder to magnetise depending on which way the object is rotated.

For most magnetically anisotropic materials, there are two easiest direction to magnetise the material, which are a 180° rotation apart. The line parallel to these directions is called the easy axis. In other words, the easy axis is an energetically favourable direction of spontaneous magnetisation. Because the two opposite directions along an easy axis are usually equivalently easy to magnetise along, and the actual direction of magnetisation can just as easily settle into either direction, which is an example of spontaneous symmetry breaking.

# Magneto crystalline anisotropy : The atomic structure of a crystal introduces preferential direction for magnetisation.

# Shape anisotropy : When a particle is not perfectly spherical, the de magnetising field will not be equal for all directions, creating one or more easy axis.

# Exchange anisotropy : Occurs when antiferromagnetic material and ferromagnetic material interact.