This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Despite being known for more mundane uses such as sticking notes to refrigerators or keeping bags shut, magnetization is one of the most fundamental and useful properties of a material. Indeed, it forms the physical basis for storing most of our digital information, encoding the bits used in hard drives, computer memories and credit cards.
In a new study published in the journal Nature Communications, Illinois researchers have found a noninvasive way to control magnetization on the order of trillionths of a second in the ferromagnetic semiconductor chromium germanium telluride (Cr₂Ge₂Te₆, or CGT). Their technique uses ultrafast laser pulses to steer CGT's magnetization around in time, taking advantage of an effect that couples its conduction electrons to its magnetic states. A material's magnetism arises when subatomic "arrows" called magnetic dipoles combine to form a net quantity called the magnetization, which points in the average dipole direction like a macroscopic compass needle.
In digital storage media, different magnetization orientations are used to encode information as bits. Of course, not only must these bits be stored, but they also must be switched in a controlled way, such as when modifying a computer file. A conventional way to change a material's magnetization is to apply an external magnetic field, which can reorient the magnetization much like a compass aligns with Earth's field to point north.
But former Illinois physics graduate student Yinchuan Lv said that these conventional approaches face practical limitations in switching speed, motivating researchers to explore alternatives. Now a postdoctoral research associate at SLAC National Accelerator Laboratory, Lv explained, "Using light to control magnetization is one of the frontier topics in applied physics today. Ultrafast laser pulses can excite electrons on femtosecond timescales, opening up the possibility of manipulating magnetic states much faster than conventional approaches." Illinois physics professor Fahad Mahmood noted, however, that despite their speed advantage, "many of these optical techniques rely on heating the material or on specific requirements, such as using circularly polarized light." Plus, light's electric field primarily interacts with a material's electrons through their charge rather than directly with the material's magnetization.
In certain materials such as CGT, however, spin-orbit interactions—which link an electron's intrinsic magnetic dipole, or spin, to its orbital motion—provide a pathway for light to influence magnetic order effectively. Illinois physics postdoctoral research associate Joe Meese described, "CGT's magnetization is particularly sensitive to perturbations and displays strong spin-orbit coupling. Some experiments have shown that one can detect CGT's magnetic behaviors with circularly polarized light, with hints that nonthermal optical processes are at play." However, CGT is centrosymmetric, meaning that its atoms are symmetrically arranged around a common center point.
This symmetry forbids certain types of direct coupling between light's electric field and magnetization, making it challenging to control magnetization using linearly polarized light. Nevertheless, spin-orbit interactions remain present in CGT, opening the door to alternative mechanisms through which light can influence its magnetism. Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. d research that matter—daily or weekly.
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