Physicists have long believed that it is impossible to alter the magnetic properties of rare earth elements. However, for the first time, a new study shows that laser pulses have the power to excite electrons that govern the magnetism of rare earth materials. 

These findings can lead to the development of better, faster, and more energy-efficient data storage devices in the future. 

The study authors achieved this feat using two powerful X-ray lasers, EuXFEL (European X-ray Free-Electron Laser) and FLASH (Free-Electron Laser in Hamburg). Both lasers are located in Hamburg, Germany, and are capable of producing ultrashort X-ray pulses.

“These X-ray sources allow us to observe elementary processes in magnetic materials on time scales of a few femtoseconds. A femtosecond (10-15 s) is one-millionth of a billionth of a second,” the study authors said.

X-ray lasers make electrons switch their orbital state

The magnetic properties of rare-earth elements are decided by the activity of their 4f electrons (electrons located in the 4f orbital of an atom). However, “Excitations of 4f electronic states in rare-earth (RE) metals have not been considered to contribute to magnetization dynamics so far,” the researchers note.

This is because until now, scientists haven’t yet figured out a way to influence the activity of these electrons. The study authors performed an interesting experiment to target the 4f electrons. 

They collected some samples of terbium (Tb), a rare-earth metal with eight electrons in its 4f orbitals. Next, they exposed the samples to X-ray laser pulses from FLASH and EuXFEL and studied the metal’s electronic structure using X-ray spectroscopy.

The laser pulses triggered the redistribution of 4f electrons and caused a change in terbium’s magnetic properties for a brief duration. “We reported an ultrafast change of 4f orbital states, based on inelastic electron-electron scattering between itinerant 5d and localized 4f electrons,” the study authors said.

The ability to control the magnetic properties of rare-earth metals opens new avenues related to their use. For instance, these materials can now be considered for use in HAMR (heat-assisted magnetic recording) storage devices. 

HAMR is an advanced data storage technology that enhances the storage density of hard drives and allows them to store information in a faster, and more efficient way. The current generation of HAMR devices employs metal alloys containing platinum, iron, cobalt, etc. 

Replacing these alloys with rare-earth metals can further improve the storage density, thermal stability, and energy efficiency of HAMR hard drives.

“With the much stronger rare-earth magnets, an ultrashort laser pulse could now excite the 4f electrons and enable switching—an electronic effect that would be even faster and more efficient than the heating mechanism in HAMR memory,” the study authors note.

However, the current study reveals a way to briefly alter the magnetic properties of rare-earth metals. Whether this method can also cause long-term changes is yet to be seen. 

Hopefully, further research will provide answers to many such questions and reveal more exciting applications of rare-earth metals with excited 4f electrons. 

The study is published in the journal Science Advances.