This chordal sequence (min, min/maj7, min7, min6) is commonly known as a minor “line cliche.” This progression is usually voiced so that there is a descending chromatic line starting from the tonic moving down to the minor 6 (i.e. in D minor the line goes D, C#, C, B). This device was used regularly by Django and has become even more common among contemporary Gypsy jazz guitarists. See my transcriptions of Improvisation #1, J’Attendrai, Just Relax, and Gypsy Etude #3 to see how Django and other Gypsies use major and minor line cliches to create harmonic movement.
This example of a line cliche places the chromatic line in the top voice. Its a great way to make a minor chord more interesting. Especially when you have to sit on one chord for 2 bars or more. In the audio example I play the line cliche twice: First time as written and then the second time I play a common rhythmic variation. This particular line cliche is commonly used by Dutch Gypsies such as Stochelo Rosenberg, Jimmy Rosenberg, Paulus Schafer, and Martin Limberger.