Insight into the rapid emergence of magnetization

Insight into the mystery of magnetism

How fast does the material generate magnetization?Credit: Lancaster University

The rate at which the material is magnetized has been discovered by an international team of scientists.

Researchers at the University of Lancaster, the University of California, San Diego, the Moscow Institute of Physical Technology, and the University of Radbaud shed light on one of the most interesting questions about magnetism.

Their research is Nature Communications..

Researchers have investigated a common magnetic alloy of iron and rhodium (FeRh) that exhibits transitions in both structure and magnetism when heated just above room temperature. At room temperature, FeRh is antiferromagnetic and therefore has no net magnetization, but when heated slightly above room temperature, the material becomes ferromagnetic.

Researchers have discovered that FeRh transitions to a ferromagnetic phase in three steps:

  • Excitation of laser pulse induces many small magnetic domains in the material
  • Magnetization of all domains aligns along one particular direction
  • It can be said that the individual domains have grown and merged into a large single domain, where the material has transitioned to its ferromagnetic phase.

Knowledge of the various stages in inducing a well-defined magnetization with optical pulses and the corresponding timescales offers the possibility of using FeRh in data storage technologies in the near future.

For example, FeRh can be used as a storage medium for heat-assisted magnetic recording (HAMR). This is a technique that uses both external heat and a local magnetic field to store information in much denser bits, which are small magnetic regions where information is stored.

Dr. Rajasekhar Medapalli, a physicist at Lancaster University, said, “Understanding the details of the various stages involved in the rapid emergence of material magnetization allows scientists to develop ultra-fast and energy-efficient magnetic data storage techniques. It helps. “

In this study, a powerful ultrashort laser pulse was used to rapidly heat FeRh with a short artificial stimulus lasting only one trillionth of a second. Due to the interaction with the material, the laser pulse raised the temperature by hundreds of degrees Celsius on a timescale less than one billionth of a second.

For a long time, it has been a fascinating goal for condensed matter physics researchers to be able to control the magnetic phase transition of FeRh using this ultrafast heat, but it has been difficult to detect this transition experimentally.

To overcome this challenge, scientists have taken advantage of the fact that time-varying magnetization creates a time-varying electric field in a medium that should act as an emitter of radiation. The emitted radiation carries sensitive information about its origin, the time-varying magnetization of the sample.

Researchers used a new double-pump time-resolved spectroscopy developed at Radboud University. They adopted two laser pulses for double pumping. The first laser pulse acts as an ultrafast heater and the second laser pulse helps generate an electric field. By detecting this field in multiple timelapses between two laser pulses, researchers were able to see how fast the magnetization appeared in the material.

The quest to provide ultra-fast, energy-efficient magnetic recording is one step closer.

For more information:
G. Li et al, Ultrafast kinetics of antiferromagnetic-ferromagnetic phase transitions in FeRh, Nature Communications (2022). DOI: 10.1038 / s41467-022-30591-2

Provided by Lancaster University

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