min7 chords are constructed with the 1st, b3rd, 5th, and b7th notes of the major scale.
m(maj7) (minor major seventh) chords are constructed with the 1st, b3rd, 5th, and 7th notes of the major scale.
m(maj7) is an uncommon and strange-sounding chord, but helpful to study for theoretical purposes, and a nice specialty tool for your harmonic tool belt.
Amin7
This common Amin7 chord shape is constructed of 1 (R for root), b3, 5, and b7.