Deep inside magnetotactic bacteria, chains of tiny crystals help the microbes navigate through ocean waters, pointing them toward food or away from danger. These biological compasses have fascinated scientists for decades. Now, researchers have borrowed nature's design to build something new: microscopic magnetic "flowers" that could transform how we study the materials of tomorrow's electronics.
A team led by Dr. Sergio Valencia at the Helmholtz-Zentrum Berlin (HZB) in Germany has created these flower-shaped devices to focus magnetic fields onto samples being studied under a powerful microscope. The work, published in the journal Small, lets scientists examine materials at magnetic field strengths five times higher than was previously possible.
To understand why this matters, it helps to know how researchers currently study magnetic materials. They use a technique called PEEM — short for photoemission electron microscopy — which fires X-rays at a sample and detects the electrons that fly off. The trouble is, strong magnetic fields bend those flying electrons, blurring the image. For decades, scientists could only study materials under weak magnetic fields up to 30 millitesla (mT), about the strength of a fridge magnet.
That limit meant researchers could only see "soft" magnetic materials — the kind you find in simple applications. "Hard" and "semi-hard" magnetic materials, which are crucial for better electronics, stayed hidden from view.
Valencia's solution was to design tiny magnetic flux concentrators (MFCs) shaped like flowers with multiple petals. When scientists apply an external magnetic field, these devices squeeze and focus it into their center, much like a magnifying glass concentrates sunlight onto a single bright point. The sample sits right in that focused spot.
With this setup, the team achieved imaging at 150 mT — five times the old limit. The local field amplification reached a factor of 5, and Valencia believes the geometry could theoretically boost fields by up to 30 times with further tweaks.
The researchers tested their flower power on two remarkable samples from BESSIS II, Germany's national synchrotron facility. First, they imaged a natural chain of magnetic nanoparticles, each about 45 nanometers wide, produced by magnetotactic bacteria. Then they examined something much older: a 60-million-year-old fossilized magnetic crystal roughly 2 micrometers in size. Using polarized X-rays, they could see the magnetic patterns inside both samples in unprecedented detail. For the ancient fossil, they observed how its magnetic domain structure evolved — a first in scientific literature.
Looking ahead, these magnetic flowers could open doors to studying entirely new types of materials: artificial spin ice, antiferromagnetic spintronic devices, and 2D van der Waals magnets — ultra-thin materials that could power quantum computers and other futuristic gadgets. By expanding the accessible range of magnetic fields, researchers now have a powerful new tool to peek at the invisible magnetic secrets hiding inside materials that could one day store your data using far less energy than today's computers.