Magnets are common in everyday life, from holding notes on a refrigerator to powering various technologies. They possess an invisible field that exerts force on certain materials. Not all materials, even metals, respond to this magnetic force in the same way. Some exhibit a strong pull, while others show little to no interaction.
Metals with Strong Magnetic Attraction
The metals most strongly attracted to magnets are iron, nickel, and cobalt. These elements are known as ferromagnetic materials, a term derived from the Latin word ‘ferrum’ for iron. Ferromagnetism arises from the unique arrangement of electrons within the atoms of these metals. Each atom acts like a tiny magnet due to the spin of its electrons, and these atomic magnets spontaneously align within small regions called magnetic domains.
In an unmagnetized ferromagnetic material, these domains are randomly oriented, canceling out their collective magnetic effects. When an external magnetic field is applied, the domains that are already aligned with the field grow larger, and the misaligned domains rotate to align with the external field. This alignment of domains creates a strong internal magnetic field within the material, resulting in the powerful attraction observed. Once the external field is removed, some of this alignment remains, which is why these metals can become permanent magnets themselves.
Metals Not Attracted to Magnets
Many common metals, unlike iron, nickel, and cobalt, do not exhibit a noticeable attraction to magnets. Examples include aluminum, copper, brass, gold, silver, zinc, and lead. These metals display different magnetic behaviors, primarily paramagnetism or diamagnetism, which are much weaker than ferromagnetism.
Paramagnetic metals, such as aluminum and platinum, are very weakly attracted to strong magnetic fields. Their atoms possess individual magnetic moments, but these moments do not align spontaneously to form domains. Instead, they only align temporarily and very slightly when an external magnetic field is present, losing their magnetic properties as soon as the field is removed. Diamagnetic metals, including copper, gold, and silver, exhibit a slight repulsion from magnetic fields. This occurs because the electrons within these materials adjust their orbits when exposed to a magnetic field, creating a tiny, opposing magnetic field that pushes against the external one.
Factors Affecting Magnetic Behavior
A metal’s magnetic behavior can be influenced by several factors. Purity matters, as impurities or non-magnetic elements can disrupt magnetic domains, reducing attraction. Alloys, mixtures of two or more metals, often have different magnetic properties than their components.
For instance, stainless steel, an iron alloy, can be magnetic or non-magnetic depending on its composition and crystal structure. Austenitic stainless steels, with nickel and chromium, often have a non-magnetic structure. Ferritic and martensitic stainless steels, with different compositions, retain their magnetic properties because their iron atoms support ferromagnetism. Temperature also affects magnetism; ferromagnetic materials lose strong magnetic properties if heated above the Curie temperature, as thermal energy disrupts domain alignment.
Real-World Uses of Magnetic Metals
The magnetic properties of certain metals are used in many applications. Electromagnets, relying on iron cores, lift heavy metallic objects in scrapyards. Compasses, navigation tools, use a small, permanently magnetized needle, often iron or an iron alloy, to align with Earth’s magnetic field, indicating direction.
Magnetic metals are also used in data storage. Hard disk drives store information by magnetizing tiny regions on a platter coated with ferromagnetic material. Refrigerator magnets, a common household item, are made from iron oxides or other composite materials that exhibit strong permanent magnetism.