Is it obligatory to pause between the words "Ar-Raheem" (the Most Merciful) and "Malik" (Sovereign) in Surat Al-Fatiha to separate the two mims, or is it permissible to join them, and the recitation still be correct?

It is permissible to connect the words (Ar-Rahim) and (Malik) without stopping, but it is better to stop, following the prophetic guidance (Sunnah) of pausing at the end of a verse. The Prophet, peace and blessings be upon him, would break his recitation, saying: "All praise is due to Allah, Lord of the worlds," then he would stop. "The Most Gracious, the Most Merciful," then he would stop. And he would recite: "Sovereign of the Day of Judgment."