The new partition is mounted to a different folder, which thus uses the default permissions. See: [HowTo] Use multiple partitions / drives in your Manjaro installation
An issue i have with your output is that the “partition” seems configured on the drive – see the missing digit at the end of the name. 
If you can’t manage in the terminal, there are graphical tools available as @straycat suggested. See here for a long read: Partitioning - ArchWiki