If it is a localized area you need to weld there are hand held units that can demag a small area (6" square). I reccomend you contact someone like Magnaflux. They do magnetic particle inspection but part of the process is to demagnitize everything they mag, some of these items are quite...
Eddy Current tests work similar to what you are seeing. Inducing a low magneic field into a part can and will show differences in heat treat. this is one of the reject criteria for many eddy current tests. So low flux levels are different for varring heat treatments.
Check out a machine called a "gaussbuster" Do a search on the internet. I beileve they even have a service that will rent the unit, or they will come to your facility and degauss the machine. Good Luck
For the magnetic force you will need to look at amperage and curreent type. The amperage multiplied by the number of turns pretty close to a linear relation ship to the magnetic field intensity. If both coils get 5 amps there is an 85 (ampere turn) difference. The more amps ther greater the...
assuming you have made a small eletric crane with a DC source, the key is to eliminate all ferreous materials except the part you are holding. When the field turns off the part will drop. If you want the part to drop instantly... If you want to demagntize the part then the previous answer to...
Demag is black magic. If you can settle for circular magnetism (which will not have a detectable north and south pole) you may be able to reorientate the field with an electric welder. Do you know how strong the field is, and in what direction the rail is pointing? If the rail is facing...