Good day

I am trying to understand what scale/mode is created by raising the fourth of a natural minor. It sounds quite dark. I understand that natural minor is the Aeolian mode of the major scales, thus, natural minor cannot have its own sets of modes, is this right?

Regardless, the piece of music center on the tonic, in this case A minor in the left hand on the piano with many diatonic chords of A minor in the right hand, all of which has no sharp or flats, thus pure A natural minor. So tonal center is kept in A and in a minor scale throughout, but then there is a F dominant 7th chord that resolves back to Am. Surely this must be a modal change? The F7 chord is F A C D#. The Mixolydian scale of F has a Bb and Eb. The piece I am playing has no B flats. I don't believe the gypsy scale nor double harmonic scale explained this case.

By all means, correct me if I'm wrong.
Thank you in advance for any explanations.