Low-cost, pseudo-Halbach dipole magnets for NMR

[Display omitted] •Strong, low-homogeneity magnets constructed using low-cost materials and simple engineering.•Apply in NMR experiments where field strength is a priority over uniformity, e.g. prepolarization.•Demonstrated use of the magnet in zero-field NMR spectroscopy. 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 [13C]-methanol prior to detection of its high-resolution NMR spectrum at zero field (measurement field below 10-10T), where signals appear at multiples of the carbon-hydrogen spin-spin coupling frequency 1JCH=140.7(1)Hz.