What is meant by 'antiferro-magnetism'?

Explanation

### Step-by-Step Text Solution:

1. **Definition of Antiferromagnetism**:
Antiferromagnetism is a type of magnetism observed in certain materials where adjacent ions or atoms that behave like tiny magnets (due to their unpaired electrons) align themselves in opposite directions. This means that their magnetic moments are oriented anti-parallel to each other.

2. **Alignment of Magnetic Moments**:
In antiferromagnetic materials, at relatively low temperatures, the magnetic moments of the adjacent ions align in such a way that they cancel each other out. This results in a net magnetic moment of zero for the entire material, meaning it does not exhibit gross external magnetism.

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