Paramagnetic and diamagnetic describe two opposite ways materials respond to a magnetic field. Paramagnetic materials are weakly attracted toward a magnet, while diamagnetic materials are weakly repelled. The difference comes down to one thing at the atomic level: whether a material has unpaired electrons.
The Core Difference: Unpaired vs. Paired Electrons
Every electron behaves like a tiny magnet because of a property called spin. In most atoms, electrons pair up in orbitals, and when two electrons share an orbital, their spins point in opposite directions and cancel each other out magnetically. An atom where all electrons are paired has no permanent magnetic moment. That makes it diamagnetic.
An atom with one or more unpaired electrons, however, retains a small net magnetic moment. That makes it paramagnetic. The simple rule of thumb used in chemistry: if every electron in an atom, ion, or molecule is paired, the substance is diamagnetic. If any electrons are unpaired, it’s paramagnetic.
How Paramagnetic Materials Behave
In a paramagnetic material, the unpaired electrons act like tiny bar magnets oriented randomly in every direction. Without an external magnetic field, these random orientations cancel out, so the material shows no magnetism on its own. Apply a magnetic field, though, and those tiny magnets partially line up with it, creating a weak attraction toward the field’s source.
The alignment is never total. Heat energy constantly jostles the atoms and randomizes their orientations, which is why paramagnetic effects get stronger at lower temperatures. This relationship is described by Curie’s Law: as temperature drops, the magnetic susceptibility of a paramagnetic material increases because thermal energy has less power to scramble the alignment.
Common paramagnetic materials include aluminum, platinum, titanium, lithium, magnesium, sodium, and oxygen gas. Molecular oxygen is a particularly interesting example because it remains paramagnetic even as a frozen solid, since its molecules contain unpaired electrons regardless of phase. Iron oxide (FeO) has one of the stronger paramagnetic responses among common materials, with a magnetic susceptibility roughly 3,000 times greater than that of aluminum.
How Diamagnetic Materials Behave
Diamagnetic materials have no permanent magnetic moment at all. When you place them in a magnetic field, the field slightly alters the motion of their electrons in a way that creates a tiny induced magnetic moment pointing in the opposite direction. This is a consequence of electromagnetic induction: the response always opposes whatever caused it. The result is that diamagnetic materials are very weakly pushed away from magnets.
Every material is diamagnetic to some extent. It’s a universal property. But in materials with unpaired electrons, the much stronger paramagnetic effect overshadows the diamagnetic contribution entirely. Diamagnetism only shows up as the dominant behavior when all electrons are paired and there’s nothing stronger to mask it.
Common diamagnetic materials include water, copper, silver, gold, bismuth, lead, mercury, diamond, and table salt. Bismuth has the strongest diamagnetic response of any naturally occurring element, with a magnetic susceptibility of about -16.6 × 10⁻⁵, roughly 18 times stronger than that of copper.
Magnetic Susceptibility: Measuring the Response
Scientists quantify how strongly a material responds to a magnetic field using a number called magnetic susceptibility. A material with zero susceptibility doesn’t respond at all. Paramagnetic materials have small positive values (they magnetize in the same direction as the field), and diamagnetic materials have small negative values (they magnetize opposite to the field).
Both effects are extremely weak compared to what you’d see with a refrigerator magnet. For ordinary solids and liquids at room temperature, the relative permeability (a closely related measure) typically falls between 1.00001 and 1.003. To put that in perspective, the magnetic response of aluminum, one of the more responsive paramagnetic metals, is only about 2.2 × 10⁻⁵, a tiny fraction above zero. Water comes in at -0.91 × 10⁻⁵, a tiny fraction below. Neither will noticeably stick to or jump away from a magnet under everyday conditions.
This is what separates both paramagnetism and diamagnetism from ferromagnetism, the powerful permanent magnetism of materials like iron and nickel. Ferromagnetic materials have susceptibility values thousands of times larger.
Where This Matters in Real Life
The most familiar application of paramagnetism is in MRI scans. When doctors need better contrast in an MRI image, they often inject a contrast agent based on the element gadolinium. Gadolinium is strongly paramagnetic, and its unpaired electrons interact with nearby water molecules in your body, altering the magnetic signal those molecules produce. This makes certain tissues, tumors, blood vessels, or areas of inflammation show up more clearly on the scan. Different formulations target different parts of the body, from general tissue imaging to detailed views of the liver or blood vessels.
Diamagnetism has a striking demonstration in physics: levitation. Because diamagnetic materials are repelled by magnetic fields, a strongly diamagnetic material placed above a powerful magnet can hover in stable equilibrium. Researchers have achieved this with pyrolytic graphite (a specially structured form of carbon with an exceptionally strong diamagnetic response), levitating pieces weighing over a gram using only permanent magnets with no power source at all. It’s one of the only ways to achieve completely passive, stable levitation.
Superconductors take diamagnetism to its extreme. A superconductor is a perfect diamagnet: it completely expels magnetic fields from its interior rather than just weakly opposing them. This is known as the Meissner effect, and it’s what makes those famous demonstrations possible where a magnet floats above a superconducting disk cooled with liquid nitrogen.
How to Tell if an Element Is Paramagnetic or Diamagnetic
If you’re working through a chemistry problem, the process is straightforward. Write out the electron configuration of the atom or ion, filling orbitals according to the standard rules. Hund’s rule is the key one here: electrons fill orbitals of equal energy one at a time, each with the same spin direction, before any orbital gets a second electron. Once you’ve mapped out the configuration, check whether any orbitals contain just one electron. If yes, the atom is paramagnetic. If every orbital has a pair, it’s diamagnetic.
Most transition metals are paramagnetic because their d orbitals are partially filled, leaving unpaired electrons. Elements with completely filled electron shells, like the noble gases, or elements whose bonding results in full pairing, like many main-group metals in their common oxidation states, tend to be diamagnetic. Copper is a notable exception: despite being a transition metal, metallic copper is diamagnetic because of the specific way its electrons are arranged in the solid state.