Low-cost, pseudo-Halbach dipole magnets for NMR.

We present designs for compact, inexpensive and strong dipole permanent magnets aimed primarily at magnetic resonance applications where prepolarization and detection occur at different locations. Low-homogeneity magnets with a 7.5mm bore size and field up to nearly 2T are constructed using low-cost starting materials, standard workshop tools and only few hours of labor - an achievable project for a student or postdoc with spare time. As an application example we show how our magnet was used to polarize the nuclear spins in approximately 1mL of pure [13 C]-methanol prior to detection of its high-resolution NMR spectrum at zero field (measurement field below 10-10 T), where signals appear at multiples of the carbon-hydrogen spin-spin coupling frequency 1 JCH =140.7(1)Hz.