Electronics/Strongest Magnetic element.
Which of the four elements have the strongest Magnetic field viz Iron, Nickel, Cobalt and Manganese?
See below link for good discussion on rare earth materials for making very strong magnets:
Of the materials you listed in your question, Iron and Cobalt are the strongest. Their magnetic strength depends greatly on the geometry of a magnet and how it is used or employed in a magnetic circuit.
Iron is very inexpensive as a material and would be best suited for low cost toys, for example, whereas Cobalt may be superior in usage but cost is much higher than iron based metals.
And usage or purpose of the magnetic material makes lots of difference. If it is being used as an insulator for magnetic fields the selection of material criteria is quite different for being a magnetic force material.
Hope this will help you.