Talks - Orbitronics 2022 - Mathias KLÄUI, University of Mainz

Summary

The speaker discusses experimental results in the field of spintronics, focusing on the challenges faced by experimentalists in advancing beyond current technology. They delve into the potential of spin-orbit torques and the role of orbital angular momentum, highlighting recent discoveries that suggest a significant increase in efficiency compared to traditional spin transfer torques. The talk emphasizes the importance of collaboration between theorists and experimentalists to understand the origins of observed effects and the potential for new materials to enhance performance in memory and logic devices.

Takeaways

• 😀 The speaker expresses excitement about seeing attendees in person after a period of virtual meetings.
• 🔬 The presentation focuses on experimental results and the practical challenges faced by experimentalists in the field of spintronics.
• 🌟 The speaker is from Mines and has a co-affiliation at NTNU, emphasizing the importance of understanding complex theories for practical applications.
• 🛠 There is a discussion on the limitations of spin transfer torque devices in the market, highlighting the efficiency limit of one Bohr magneton per electron.
• 📈 The potential of spin-orbit torques (SOTs) to overcome these limitations by allowing the transfer of more than one Bohr magneton per electron is introduced.
• 🔍 The experimental challenge of distinguishing between different types of torques (damping-like and field-like) is highlighted, as only the effective field's direction and strength can be measured.
• 🌀 The concept of orbital angular momentum and its potential to enhance torque efficiency beyond spin angular momentum alone is explored.
• 💡 The importance of collaboration between theoreticians and experimentalists to interpret experimental results and understand the origins of different torques is emphasized.
• 📚 The speaker references previous work and theoretical calculations that motivate the experimental approach to identifying and quantifying orbital effects in materials.
• 🛑 The experimental results show a significant increase in torques when certain materials like copper oxide are used, suggesting a strong orbital current generation.
• 🔧 The use of different ferromagnets in experiments reveals a unique dependence on the material, suggesting that the conversion of orbital currents to spin currents is material-specific.

Q & A

What is the main focus of the speaker's presentation?

The speaker's presentation focuses on experimental results related to spin and orbital angular momentum in materials, particularly the effects of spin-orbit torques and the potential for increasing efficiency beyond current limitations.

What is the significance of seeing 80 people 'alive in 3D' compared to 'tiles of Zoom'?

The speaker is expressing the value of in-person interactions over virtual meetings, highlighting the importance of live attendance for a more engaging and dynamic experience.

Why is the efficiency of spin transfer torque limited?

The efficiency of spin transfer torque is limited because it is fundamentally constrained by the efficiency of one Bohr magneton (h bar) per electron for spin transfer torque, which necessitates a certain amount of current to reverse the magnetization.

What is the potential advantage of orbital angular momentum over spin angular momentum in this context?

Orbital angular momentum offers the potential to transfer more than one Bohr magneton per electron, which can lead to increased efficiency in torques compared to traditional spin transfer torques.

What are the two fundamental mechanisms the speaker refers to in relation to spin-orbit torques?

The two fundamental mechanisms are the spin Hall effect, where spin-polarized electrons are scattered into a ferromagnet, and the inverse spin galvanic effect or Edelstein effect, where a non-equilibrium spin density forms and exerts a torque by exchange interaction on the magnetization.

Why is it challenging for experimentalists to identify the origin of a torque?

It is challenging because the only measurable quantities are the direction and strength of the effective field, which can have the symmetry of either a damping-like or field-like torque. The actual origin of the torque requires indirect interpretation and input from theoreticians.

What is the significance of the 16-fold increase in torques when copper oxide is added on top of platinum?

The 16-fold increase indicates a highly efficient generation of orbital currents that are converted into spin currents in the platinum layer, which then generate a significant spin-orbit torque acting on the underlying ferromagnet.

How does the speaker's research group address the experimental challenge of identifying orbital effects?

The group uses a combination of torque measurements and magneto-resistance effects, varying the thickness of different layers in their samples, and comparing results across multiple materials to infer the origins of the observed effects.

What is the importance of being able to manipulate iron cobalt boron instead of nickel in MRAM devices?

The ability to manipulate iron cobalt boron is important because it is preferred by companies for MRAM devices due to its compatibility with MgO tunnel junctions, which nickel does not offer.

What is the role of theoreticians in this field of research?

Theoreticians play a crucial role in interpreting experimental results, providing calculations and models that help experimentalists understand the underlying physics of the observed phenomena, and guiding the design of new experiments.