Rotate BLDC motor with Clark and Park transform
Your motor has a silicon steel stator core which increases the magnetic strength of the coils. Unfortunately the rotor magnets are attracted to the stator polefaces, creating a 'cogging torque' which makes the movement jerky. Here's an example of cogging torque in a 14 pole brushless motor:- 



To cancel out the cogging torque you must modify the drive current waveforms. The exact waveform required depends on the particular geometry of your motor (poleface shape, magnet size and positions, airgap etc.). In a motor with strong Neodym magnets there is a fine balance of forces, so any slight misalignments can greatly affect the cogging torque waveform. Therefore for best results you will have to customize the drive waveforms to match your particular motor. 

However without any feedback it is not possible to measure the actual cogging torque, so all you can do is try different waveforms until you get the smoothest movement. I would start by mixing in varying amplitudes and phase of 3rd and 5th harmonics.