You should properly name it the Hall effect.
For more info read this Wikipedia article to understand how it should be used in sentences.
At the beginning of a sentence:
The Hall effect was discovered in 1879.
In the middle of a sentence:
One very important feature of the Hall effect is that it differentiates between positive charges moving in one direction and negative charges moving in the opposite.
At the end of a sentence:
The absence of the free transverse boundaries renders the interpretation of the Corbino effect simpler than that of the Hall effect.
Used as an adjective in a sentence:
Hall effect devices produce a very low signal level and thus require amplification.