What makes a material ferromagnetic

Ferromagnetism being the most common the average person recollects. That is because most people have encountered permanent magnets sometime in their life, and they are made of ferromagnetic material.

This is really similar to paramagnetic material but with one important difference that separates them. Paramagnetism has no net magnetic field because the spins of the electrons are pointing in all different direction. This means that when a strong magnet of either positive or negative attraction is placed near the paramagnetic material a partial alignment of the spins will result in a weak attraction. Where as in ferromagnetism the spins of the electrons are all pointing in the same direction.

This is what causes permanent magnets to attract through opposite poles, south to north and vise versa, as well as repel when the same poles are facing each other. The most common ferromagnetic materials are cobalt, iron, nickel, along with Lodestone a naturally magnetized mineral and other rare earth metal compounds. A common usages of ferromagnetic materials affecting our everyday lives is through magnetic storage in the form of data.

Otherwise considered non-volatile storage since data cannot be lost when the device it is not powered. An advantage of this storage method is that it is one of the cheaper forms of storing data, as well as having the ability to be re-used.

This is all possible because of Hysteresis. Once ferromagnetic materials are magnetized toward a specific direction it loses the ability to lose its magnetization Hysteresis. Meaning it will not be able to go back to its original state without any magnetization. But another opposite magnetic field can be applied which would result in the creation of a hysteresis loop, as seen in figure 1. This ultimately is the unique effect that allows these materials to retain data, after the ma gnetizing field is dropped to zero.

If the electrons have the same spin then they will occupy different orbitals and therefore have less Coulomb repulsion as they will be further apart. In this way, the exchange energy the energy due to the repulsion between the two electrons is minimsed. Therefore the Coulomb repulsion force favours the parallel alignment of all the electron spins as the exchange energy is minimised.

The above rules help to explain the strong ferromagnetic order seen in iron, cobalt and nickel. Maybe is there an explaination with the Ising model or do I have to consider more advanced models for describing how ferromganetism depends on the composition of metals?

This is a really difficult question that a lot of people are trying to answer, because the ability to predict strong magnetic materials would be really useful for device applications.

Ferromagnetism comes from the atoms having multiple valence electrons with parallel spins. Metals typically have valences on multiple shells, which increases the electrical interactions. Neodymium has an absurdly high amount, 7 to be exact, of unpaired electrons, which gives it it's magnetic properties. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Learn more. Why are some materials more ferromagnetic than others? Ask Question. Electromagnets are employed for everything from a wrecking yard crane that lifts scrapped cars to controlling the beam of a km-circumference particle accelerator to the magnets in medical imaging machines See Figure 3.

Figure 3. Instrument for magnetic resonance imaging MRI. The device uses a superconducting cylindrical coil for the main magnetic field. Figure 4 shows that the response of iron filings to a current-carrying coil and to a permanent bar magnet. The patterns are similar. In fact, electromagnets and ferromagnets have the same basic characteristics—for example, they have north and south poles that cannot be separated and for which like poles repel and unlike poles attract.

Figure 4. Iron filings near a a current-carrying coil and b a magnet act like tiny compass needles, showing the shape of their fields. Their response to a current-carrying coil and a permanent magnet is seen to be very similar, especially near the ends of the coil and the magnet.

Combining a ferromagnet with an electromagnet can produce particularly strong magnetic effects. See Figure 5. Whenever strong magnetic effects are needed, such as lifting scrap metal, or in particle accelerators, electromagnets are enhanced by ferromagnetic materials.

Limits to how strong the magnets can be made are imposed by coil resistance it will overheat and melt at sufficiently high current , and so superconducting magnets may be employed.

These are still limited, because superconducting properties are destroyed by too great a magnetic field. Figure 5. An electromagnet with a ferromagnetic core can produce very strong magnetic effects. Alignment of domains in the core produces a magnet, the poles of which are aligned with the electromagnet.

Figure 6 shows a few uses of combinations of electromagnets and ferromagnets. Ferromagnetic materials can act as memory devices, because the orientation of the magnetic fields of small domains can be reversed or erased. Magnetic information storage on videotapes and computer hard drives are among the most common applications. This property is vital in our digital world.