A pump unit with at least one impeller, comprising a magnetic coupling (100, 200), wherein the coupling is mechanically connected to the at least one impeller via an inner rotor and where an outer rotor is connected to an electrical machine arranged to produce a rotational torque, said pump being arranged to circulate a fluid by the impeller, the magnetic coupling comprising - an outer rotor including a plurality of permanent magnets (101,201) arranged to form a plurality of magnetic poles (105, 205); - an inner rotor (110, 210); - the outer rotor and the inner rotor being located coaxially to one another around an axis (130, 230) and spaced apart from one another by an air gap (150,250); - a rotor can (330,662) arranged in the air gap (250, 150), between the inner rotor and the outer rotor, so to make a dividing section between the inner and outer rotor; - the outer rotor has a cylindrical structure surrounding (120, 220) the plurality of magnetic poles (105, 205), the cylindrical structure being made of a magnetic susceptible material for conducting a magnetic flux between the plurality of magnetic poles (105, 205); - the inner rotor (110, 210) being made of a magnetic susceptible material and free of permanent magnetic material, wherein the inner rotor is formed with multiple radial projections (111, 211) acting as salient inner rotor poles distributed around the axis (130, 230) of the inner rotor; - each of the plurality of magnetic poles, comprising at least a section with a radial magnetic direction in respect of the axis (130, 230) and at least a section with a magnetic direction angled between a radial direction and a tangential direction in respect of the axis (130, 230); and - wherein the combined length of the sides of the plurality_of permanent magnets cover less than 75% of the circumference of the cylindrical structure. - an outer rotor including a plurality of permanent magnets (101,201) arranged to form a plurality of magnetic poles (105, 205); - an inner rotor (110, 210); - the outer rotor and the inner rotor being located coaxially to one another around an axis (130, 230) and spaced apart from one another by an air gap (150,250); - a rotor can (330,662) arranged in the air gap (250, 150), between the inner rotor and the outer rotor, so to make a dividing section between the inner and outer rotor; - the outer rotor has a cylindrical structure surrounding (120, 220) the plurality of magnetic poles (105, 205), the cylindrical structure being made of a magnetic susceptible material for conducting a magnetic flux between the plurality of magnetic poles (105, 205); - the inner rotor (110, 210) being made of a magnetic susceptible material and free of permanent magnetic material, wherein the inner rotor is formed with multiple radial projections (111, 211) acting as salient inner rotor poles distributed around the axis (130, 230) of the inner rotor; - each of the plurality of magnetic poles, comprising at least a section with a radial magnetic direction in respect of the axis (130, 230) and at least a section with a magnetic direction angled between a radial direction and a tangential direction in respect of the axis (130, 230); and - wherein the combined length of the sides of the plurality_of permanent magnets cover less than 75% of the circumference of the cylindrical structure.