Scientists Decode Heat Flow Mystery in Magnetic Semiconductors

Researchers have uncovered how heat moves inside magnetic semiconductors—materials crucial for spintronics, magnetic memory, and quantum technologies—solving a long-standing puzzle in condensed matter physics and opening new pathways for managing heat in next-generation electronic devices.

The breakthrough study, led by Prof. Bivas Saha at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru, provides the first direct experimental evidence linking magnetic spin fluctuations with unusual heat conduction behavior in these materials.

The findings were recently published in the journal Science Advances.

Decade-Old Physics Puzzle Explained

In most conventional semiconductors, thermal conductivity decreases as temperature rises because heat-carrying lattice vibrations—called phonons—scatter more frequently.

However, several magnetic semiconductors behave differently, displaying an unexpected increase in thermal conductivity at higher temperatures, especially above their magnetic transition temperature.

One prominent example is chromium nitride (CrN), a magnetic semiconductor widely used in protective coatings and electronic applications.

Until now, scientists had struggled to explain the microscopic mechanism behind this unusual behaviour.

Spin–Phonon Interaction Drives Heat Flow

The research team discovered that strong coupling between phonons and magnetic spin fluctuations governs heat transport in magnetic semiconductors.

Using temperature-dependent inelastic X-ray scattering experiments, the scientists directly measured phonon lifetimes in high-quality CrN thin films as the material passed through its magnetic phase transition.

These experiments revealed that:

• Acoustic phonons, which carry most of the heat, interact strongly with magnetic spin fluctuations near the Néel temperature

• This interaction causes strong damping of phonons when magnetic order is present

• As temperature increases further and magnetic order weakens, phonon lifetimes unexpectedly increase

This phenomenon results in higher thermal conductivity at elevated temperatures, contrary to normal semiconductor behaviour.

Interestingly, optical phonons followed standard temperature-dependent patterns, confirming that spin fluctuations are the key driver of the anomalous heat transport.

Advanced Simulations Confirm the Mechanism

The experimental results were reinforced through atomistic spin-dynamics simulations and first-principles theoretical calculations.

Together, the experimental and computational approaches established a clear microscopic framework explaining how magnetic fluctuations influence heat conduction in magnetically ordered materials.

"This work provides the first direct experimental evidence connecting spin fluctuations with enhanced thermal conductivity in magnetic semiconductors," said Prof. Bivas Saha.

Implications for Spintronics and Quantum Devices

The discovery could have significant implications for future electronics and quantum technologies, where heat management is a major engineering challenge.

Efficient thermal control is essential for:

• Spintronic devices

• Magnetic memory technologies

• Quantum computing components

• High-performance electronic systems

Understanding how spin–lattice interactions regulate heat flow may allow researchers to design materials where thermal transport can be actively controlled through magnetic properties.

This could lead to faster, more energy-efficient devices with improved reliability.

Global Collaboration Behind the Breakthrough

The research involved an international collaboration between several leading institutions, including:

• JNCASR, Bengaluru

• Indian Institute of Science Education and Research (IISER), Thiruvananthapuram

• Linköping University, Sweden

The experiments were conducted at major international synchrotron facilities such as:

• SPring-8, Japan

• DESY, Germany

The study underscores India's growing presence in advanced materials science and condensed matter research.

Toward Smarter Thermal Materials

Scientists say the ability to control heat flow through magnetic interactions could enable a new generation of materials designed for precision thermal management.

Such materials may play a crucial role in future quantum technologies, spin-based computing systems, and high-power electronics, where maintaining optimal temperature is essential for performance and longevity.