A method of manufacturing a data storage device may include forming a magnetic tunnel junction layer on a substrate, irradiating a first ion beam on the magnetic tunnel junction layer to form magnetic tunnel junction patterns separated from each other, irradiating a second ion beam on the magnetic tunnel junction layer, and irradiating a third ion beam on the magnetic tunnel junction layer. The first ion beam may be irradiated at a first incident angle. The second ion beam may be irradiated at a second incident angle that may be smaller than the first incident angle. The third ion beam may be irradiated to form sidewall insulating patterns on sidewalls of the magnetic tunnel junction patterns based on re-depositing materials separated by the third ion beam on the sidewalls of the magnetic tunnel junction patterns.