A glimpse into the mystery of magnetism

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June 13, 2022

(News from Nanowerk) The magnetization rate of a material was discovered by an international team of scientists. Researchers from Lancaster University, University of California San Diego, Moscow Institute of Physics and Technology, and Radboud University have shed light on one of the most intriguing questions in magnetism : how fast can magnetization be created in a material?

Their research is published in Nature Communication (“Ultrafast kinetics of the antiferromagnetic-ferromagnetic phase transition in FeRh”).

The researchers examined the common magnetic alloy of iron and rhodium (FeRh) which exhibits a transition in both structure and magnetism when heated to just above room temperature. At room temperature, FeRh has no net magnetization due to its antiferromagnetic nature, but when heated just above room temperature, the material becomes a ferromagnetic. The researchers found that FeRh undergoes a transition to its ferromagnetic phase in three steps:-

  • the excitation of the laser pulse induces a large number of tiny magnetic domains in the material
  • the magnetization of all domains aligns along a particular direction
  • the individual domains grow to merge into a single large domain where the material can be said to have undergone a transition to its ferromagnetic phase.
  • Knowledge of the different steps involved and their corresponding time scales to induce a well-defined magnetization with a light pulse opens the possibility of using FeRh in a near future data storage technology.

    For example, FeRh can be used as a storage medium in heat-assisted magnetic recording (HAMR), a technology that uses both external heat and local magnetic fields to store information with much higher bit density. elevated – tiny magnetic regions where information is stored.

    Physicist Dr Rajasekhar Medapalli from Lancaster University said: “Understanding the details of the different steps involved in the rapid emergence of magnetization in a material helps scientists to develop ultra-fast and energy-efficient magnetic data storage technologies. in energy.”

    The research involved the use of intense ultrashort laser pulses to rapidly heat FeRh in a brief artificial stimulus lasting only one quadrillionth of a second. Upon interacting with the material, the laser pulse increased the temperature by a few hundred degrees Celsius at time scales of less than a billionth of a second.

    For a long time it has been a fascinating goal for condensed matter physics researchers to use this ultrafast heat and be able to control the magnetic phase transition in FeRh, but experimentally detecting this transition has been a challenge.

    To overcome the challenge, the scientists used the fact that time-varying magnetization produces a time-varying electric field in a medium that should act as an emitter of radiation. The emitted radiation contains sensitive information about its origin, i.e. time-varying magnetization in the sample.

    The researchers used the new dual-pump time-resolved spectroscopy technique developed at Radboud University. They used two laser pulses for double pumping: while the first laser pulse serves as an ultrafast heater, the second helps generate an electric field. By detecting this field at several time intervals between the two laser pulses, the researchers were able to observe how quickly the magnetization emerges in the material.

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