Most materials we use in everyday life expand when they are heated.
Metals, plastics, and many other materials grow slightly larger as the temperature rises and shrink back again when they cool.
But scientists have now developed a new material with a surprising property: it actually becomes smaller when heated.
The discovery could help scientists design new types of computer memory that use far less energy than current technologies.
The research focuses on a special class of materials called multiferroics.
These unusual materials combine different physical properties—such as electrical and magnetic behavior—inside a single substance.
Because they can respond to both electricity and magnetism, they are considered promising candidates for future electronic devices.
One of the best-known multiferroic materials is bismuth ferrite (BiFeO₃). This material can store electric charge like a capacitor, but it also has magnetic properties similar to those found in magnets.
Scientists have long been interested in it because electrical signals can change its internal electric polarization, and this change can also affect its magnetism.
This combination could be extremely useful for memory technology. Electricity can switch the stored information using very little energy, while magnetism makes it easy to read that information.
In theory, this could allow computers to store data more efficiently while using much less power.
However, there has been a major obstacle. Inside bismuth ferrite, iron atoms behave like tiny magnets. But instead of pointing in the same direction, these microscopic magnets rotate gradually in a wave-like pattern.
Because of this unusual arrangement, their magnetic effects cancel each other out, meaning the material appears to have almost no overall magnetism.
Scientists previously tried solving this problem by replacing some of the iron atoms with cobalt. This changed the arrangement of the tiny magnets and created weak magnetism at room temperature. Unfortunately, the magnetic signal remained fragile and could easily be disrupted.
A research team led by Professor Masaki Azuma at the Institute of Science Tokyo decided to try a different approach. Using theoretical calculations and experimental work, they redesigned the material by replacing some of the iron atoms with heavier elements such as ruthenium and iridium.
This chemical adjustment was not simple. Because these elements carry a different electrical charge, the team also replaced some of the bismuth atoms with calcium to keep the material electrically balanced.
The result was a major improvement. The tiny magnetic moments inside the material began aligning more consistently, creating a stable magnetic state that could be detected from outside the material. In fact, the new material showed magnetic stability about four times stronger than earlier versions that used cobalt.
During further experiments, the researchers noticed something unexpected. When the material was heated, it shrank slightly instead of expanding. This rare effect, called negative thermal expansion, occurred within normal temperature ranges.
This unusual behavior could be useful in precision devices. If a material that shrinks with heat is combined with materials that expand, the two effects could balance each other out and reduce mechanical stress caused by temperature changes.
The discovery highlights how carefully designing the elements inside a material can dramatically change its properties. According to Azuma, the team achieved the magnetic behavior they were aiming for—and also uncovered an unexpected phenomenon that could lead to new technological applications.
In the future, materials like this could play an important role in next-generation memory devices that store information reliably while using far less electricity than today’s technologies.
