Minor 7b5 chords are also referred to as Half Diminished chords, as they nearly have the same notes. The Diminished has a bb7th whereas the m7b5 only has a b7th in the formula. Just as a Diminished chord is symbolised by a small circle , the m7b5 symbol is a small circle with a line through it, indicating that it is " Half Diminished ".
You may have noticed that these chord shapes are the same as those for Minor 6th chords. The notes are the same however you must remember that the Tonics are different. It is very useful to remember that every m7b5 chord can also be a minor 6th chord if you use the b3 note as the new Tonic for the minor 6th chord.