There is no independent scientific research proving that a magnet will work as effective shark deterrents, no magnetic repellent products have been tested independently and proven as effective, and the reason for this is at a distance of 10 cm from the magnet there is no detectable magnet field for the shark to sense (see graph below).
Ocean Guardian is the world's only scientifically proven and independently tested electrical shark deterrent.
Both magnetic and electrical fields are known as the Lorentz force, and it is the Lorentz force which sharks use their ampullae of lorenzini (electro receptors) to find food at close range. All living creatures have this field with scientists stating that sharks electro receptors are sensitive to one billionth of a volt.
It is difficult to compare measurements between the two fields because magnetic fields relate to a charged particle moving through a field, and electrical fields refer to a stationary particle with a charge. Ignoring for a moment the technical conversions and lets pretend that the magnetic particle was stationary, this means that 1 V/M = 1 N/C = 1 T NOTE: We are simply aiming to compare both fields strengths, not quite correct but ok for this discussion.
at a distance of
A medium block magnet shown below of at a distance of 2 centimeters (<1") and a field strength of at a distance of 10 centimeters (3.9").
A shark will be approximately ten (10) centimeters (3.9”) from a magnet repellent before sensing the magnetic field.
A shark will be approximately six hundred (600) centimeters (19' 8") from an Ocean Guardian before sensing the electrical field.
In addition to the distance, it is extremely unlikely that a magnetic field strength would deter a shark of interest, which explains why no independent scientific research exists using a magnet as an effective shark deterrent.