A magnetic filter device capable of separating contaminant material from a working fluid. The device includes an inlet to allow fluid to flow into the device and an outlet to allow fluid to flow out of the device. The filter further includes an elongate magnetic core comprising at least four columns of magnets. At least two magnetic columns include a north polarity extending over the length of the columns and at least two columns have a south polarity extending substantially the length of the columns. The four columns are positioned lengthways around a central longitudinal axis of the core in alternating north and south polarity thereby generating a magnetic field of alternating high and low field intensity in the region around the magnetic core exterior.