A magnetic assembly for a nuclear magnetic resonance apparatus includes a number of primary permanent magnets 1 disposed in an array about a longitudinal axis, the arrangement and/or characteristics of the plurality of magnets being such so as to create a zone of homogeneous magnetic field at some location along the axis forward of the array (and into the material when provided). A secondary permanent magnet 7 may be located along the longitudinal axis within the array of primary magnets and may be moveable. The primary magnets 1 have a north pole and a south pole with an axis therebetween, and may be arranged such that the axis between the poles is at an angle to the longitudinal axis.