A TRACON Controller reported they descended an aircraft to an altitude below the Minimum Vectoring Altitude.

Narrative

I was vectoring numerous aircraft of various performance characteristics for sequence to Runway 21. I attempted to create space in the sequence for slower traffic ahead by vectoring Aircraft Y off his RNAV STAR. I instructed him to turn to a heading of 210 and maintain an altitude of 12;000 feet for high terrain near him. My intention was to vector him back to the STAR and then to the RNAV Z fix for Runway 21. Once I had sufficient space in the sequence; I instructed Aircraft Y to descent to 10;000 feet. When the aircraft was nearing a 11;200 feet MVA at an altitude of 11;500 feet. I instructed the pilot to maintain that altitude and informed him of the MVA. He acknowledged my transmission but kept descending. I then instructed him to turn direct to the RNAV Z fix; but realized that would not keep the target out of the higher MVA. I instructed the pilot to turn right to a heading of 330 to keep him out of the higher MVA; but the targeted entered the 11;200 feet. MVA at about 10;800 ft. Instead of vectoring him to fly the RNAV Z approach; I should have kept the aircraft above the MVA and instructed him to expect the visual approach; made him fly further away from the airport; and commenced my sequence with ample time for him to descend in a timely fashion and to clear all higher MVAs before clearing him for any approach.