Magnet assembly with improved field uniformity and methods of making and using same

A magnet assembly, comprising:

• a first permanent magnet having a top surface and a bottom surface and a first magnetization direction;
• a second permanent magnet having a top surface and a bottom surface and a second magnetization direction, wherein the second permanent magnet is spaced apart from the first permanent magnet, and wherein the first and second permanent magnets are positioned and oriented such that the first and second magnetization directions are parallel;
• a first material that exhibits magnetic permeability affixed to the top surfaces of the first and second permanent magnets;
• and
• a second material that exhibits magnetic permeability affixed to the bottom surfaces of the first and second permanent magnets;
• wherein the first and second permanent magnets and the first and second materials that exhibit magnetic permeability together define a hollow field region, wherein a magnetic field direction in the hollow field region is antiparallel to the first and second magnetization directions.