Magnetism is the physical phenomenon mediated by magnetic fields that arises from the intrinsic spin of electrons and their orbital motion, causing materials to be attracted to or repelled by an applied magnetic field. If you are asking how many types of magnetism are there, the strict physics answer is five: diamagnetism, paramagnetism, ferromagnetism, antiferromagnetism, and ferrimagnetism. However, as an electrical builder or hobbyist, you will practically only interact with three of them when selecting components, designing filters, or troubleshooting power supplies.
The Five Types of Magnetism Explained
Every material on the periodic table responds to a magnetic field, but the mechanism and strength of that response vary wildly based on atomic structure. Here is the definitive breakdown of the five fundamental types, ranked by how often they matter on your workbench.
| Type | Magnetic Susceptibility ($\chi$) | Behavior in a Field | Common Materials | Bench Relevance |
|---|---|---|---|---|
| Ferromagnetism | Large, positive ($10^3$ to $10^5$) | Strongly attracted; retains magnetization | Iron, Cobalt, Nickel | High (Transformer cores, motors) |
| Ferrimagnetism | Large, positive ($10^1$ to $10^3$) | Strongly attracted; lower saturation than ferro | Magnetite, Ferrites (MnZn, NiZn) | Very High (SMPS inductors, RF chokes) |
| Paramagnetism | Small, positive ($10^{-5}$ to $10^{-3}$) | Weakly attracted; loses magnetization instantly | Aluminum, Platinum, Oxygen | Low (Mostly a nuisance in precision sensors) |
| Diamagnetism | Small, negative ($-10^{-5}$) | Weakly repelled by magnetic fields | Copper, Bismuth, Superconductors | Medium (Eddy current braking, shielding) |
| Antiferromagnetism | Small, positive (peaks at Néel temp) | Internal spins cancel out; no macroscopic field | Chromium, Manganese oxide | None (Relevant only in solid-state physics) |
What Magnetic Type Actually Changes in Your Circuit
The type of magnetism a material exhibits dictates its permeability ($\mu$) and its electrical resistivity ($\rho$). In a real circuit, this changes three critical parameters:
- Inductance Density: A ferrimagnetic core with a relative permeability ($\mu_r$) of 2,000 allows you to wind an inductor with 45 times fewer turns than an air core ($\mu_r = 1$) to achieve the exact same microhenry ($\mu H$) value.
- Core Saturation Limits: Ferromagnetic materials (like silicon steel) can handle massive magnetic flux densities (up to 2.0 Tesla) before saturating, whereas ferrimagnetic ferrites typically saturate around 0.3 to 0.5 Tesla.
- High-Frequency Losses: The electrical resistivity of the magnetic material determines how much energy is wasted as heat via eddy currents when the magnetic field alternates rapidly.
Common Confusions to Avoid
The most frequent mistake hobbyists make is confusing ferromagnetism with electromagnetism. Electromagnetism is the generation of a magnetic field via electrical current (like current flowing through a copper coil). Ferromagnetism is a material property that concentrates and amplifies that generated field. You use electromagnetism to create the field, and a ferromagnetic core to guide it.
A second major confusion is treating ferrimagnetism (ferrites) as identical to ferromagnetism (iron/steel). While both attract magnets, their internal atomic alignments and electrical conductivities are vastly different—a distinction that will melt your circuit board if ignored.
Bench Scenario: The 500 kHz Buck Converter Meltdown
To understand why distinguishing between these types matters, let us walk through a real-world failure scenario involving a high-frequency switch-mode power supply (SMPS).
The Setup
During a prototype build, a designer needed a 4.7 µH inductor capable of handling 10A RMS. To save money and time, they scavenged a toroidal core from a scrap 60 Hz mains transformer. This core was made of solid silicon electrical steel—a classic ferromagnetic material with a high saturation point and a relative permeability of roughly 4,000. They wound 12 turns of 16 AWG magnet wire, verified the inductance read 4.8 µH on their LCR meter at 1 kHz, and soldered it to the PCB.
The Numbers
At 1 kHz, the inductor looked perfect. But at the 500 kHz operating frequency, eddy current losses take over. Eddy current power loss ($P_e$) is inversely proportional to the material's electrical resistivity ($\rho$):
$$P_e \propto \frac{B^2 \cdot f^2 \cdot d^2}{\rho}$$
Solid silicon steel (ferromagnetic) has a resistivity of roughly $4.7 \times 10^{-7} \ \Omega\cdot m$. A proper Manganese-Zinc (MnZn) ferrite core (ferrimagnetic) has a resistivity of about $10 \ \Omega\cdot m$. The ferrite is 21 million times more resistive than the steel.
The Outcome
Upon applying full load, the massive alternating magnetic field at 500 kHz induced severe eddy currents inside the highly conductive solid steel core. The core essentially acted as a shorted secondary winding. Within 45 seconds, the core temperature exceeded 180°C. The heat transferred to the PCB, melting the 63/37 Sn/Pb solder on the through-hole pads, lifting the copper trace, and destroying the switching MOSFET.
What Went Wrong
The designer chose a material based purely on its permeability and saturation limit, ignoring its resistivity. For 60 Hz mains applications, solid ferromagnetic steel is fine (especially when laminated into thin sheets to break up eddy currents). But at 500 kHz, you must use a ferrimagnetic ferrite core. Ferrites are ceramic oxides; they are magnetic but electrically insulating, which chokes off eddy currents and keeps core loss density under $300 \ mW/cm^3$ at high frequencies. For a deep dive into material properties, the Georgia State University HyperPhysics database provides excellent baseline susceptibility charts.
Where You Meet These Materials in Practice
Knowing the five types of magnetism allows you to select the right off-the-shelf components or raw materials for specific electrical tasks.
- Power Transformers & Motors (Ferromagnetic): You will find laminated silicon steel (ferromagnetic) in 50/60 Hz grid transformers, microwave oven transformers, and heavy AC induction motors. The laminations are insulated from each other to mitigate eddy currents at low frequencies.
- Switch-Mode Power Supplies & RF (Ferrimagnetic): Look inside any laptop charger, ATX power supply, or Wi-Fi router. The high-frequency transformers and EMI chokes use MnZn or NiZn ferrites (ferrimagnetic) because their high resistivity prevents high-frequency burnout.
- Magnetic Shielding (Ferromagnetic): If you need to protect a sensitive Hall-effect sensor or an analog audio circuit from stray magnetic fields, you use Mu-metal. Mu-metal is a highly permeable nickel-iron ferromagnetic alloy that absorbs and redirects magnetic flux lines around the shielded volume.
- Eddy Current Braking & Levitation (Diamagnetic): Copper and aluminum are diamagnetic. When you drop a strong neodymium magnet through a thick copper pipe, the changing magnetic field induces currents in the copper that create an opposing magnetic field, slowing the magnet's fall. This exact principle is used in eddy current sensors and non-contact braking systems on roller coasters.
Frequently Asked Questions
Is neodymium a type of magnetism?
No. Neodymium is a chemical element (Nd). When alloyed with iron and boron (NdFeB), it creates a ferromagnetic material with an incredibly high maximum energy product (BH max), making it the strongest commercially available permanent magnet. The underlying physics is still standard ferromagnetism.
Why do we care about paramagnetism in electronics?
Mostly, we care about it as a source of error. In highly sensitive precision circuits, like those using fluxgate magnetometers or SQUIDs (Superconducting Quantum Interference Devices), the weak paramagnetic properties of nearby aluminum enclosures or oxygen in the air can introduce microscopic noise floors. For 99% of DIY and commercial PCB design, paramagnetism is negligible.
Can a material change its magnetic type?
Yes, temperature dictates magnetic behavior. If you heat a ferromagnetic material (like iron) past its specific Curie temperature ($770°C$ for pure iron), the thermal energy overcomes the atomic spin alignment, and it degrades into a paramagnetic material. It will no longer hold a magnetic field until it cools back down.
