A team of scientists from the Institute of Science Tokyo, led by Professor Pham Nam Hai, has developed a ferromagnetic semiconductor (FMS) that works at higher temperatures than any similar material reported so far. According to their findings, published in Applied Physics Letters (Vol. 126, Issue 16, April 24, 2025), the material reaches a Curie temperature (TC) of up to 530 K—well above room temperature.
For those not familiar, the Curie temperature is the specific temperature at which a ferromagnetic material (like iron or certain semiconductors) loses its permanent magnetism and becomes paramagnetic.
FMS materials are known for combining electrical and magnetic properties, which makes them promising for spintronic devices that use both the charge and spin of electrons. Among them, Fe-doped narrow-gap III–V semiconductors like (In,Fe)Sb and (Ga,Fe)Sb have stood out due to their potential for high TC. But bringing in a large amount of magnetic elements like iron without damaging the crystal structure has been a big challenge.
In earlier attempts, materials like (Ga,Mn)As had low TC values and couldn’t be used effectively at room temperature. While past research managed to hit a TC of 420 K, that still wasn’t enough for stable, real-world operation.
In this new study, the Tokyo team found a way around the problem. They grew thin films of (Ga,Fe)Sb using a technique called step-flow growth on GaAs (100) substrates that were slightly angled—about 10° off-axis. This method let them add up to 24% Fe without ruining the structure of the material.
Thanks to this technique, they created (Ga₀.₇₆Fe₀.₂₄)Sb films with Curie temperatures between 470 K and 530 K, the highest reported so far in FMS research.
“In the conventional (Ga,Fe)Sb samples, maintaining crystallinity at high Fe doping levels was a persistent issue. By applying the step-flow growth technique on vicinal substrates, we successfully addressed this challenge and achieved the world’s highest TC in FMSs,” said Prof. Hai.
To confirm the magnetic behavior, the team used magnetic circular dichroism spectroscopy, which checks how light interacts with spin-polarized electronic states. They also analyzed magnetization data using Arrott plots, a technique used to pinpoint the temperature where the material becomes magnetic.
The magnetic moment of each Fe atom in the sample measured around 4.5 μB, which is close to the ideal 5 μB expected for Fe³⁺ ions in a zinc blende structure. That’s about twice the magnetic moment of regular iron metal (α-Fe).
They also tested long-term durability. A thin 9.8 nm film stored in open air for 1.5 years still showed strong magnetic properties, though the TC dropped slightly to 470 K.
“Our results demonstrate the feasibility of fabricating high-TC FMSs that are compatible with room temperature operations, which is a crucial step towards the realization of spintronic devices,” Prof. Hai added. This work shows how careful control of growth methods and material design can lead to more practical and powerful semiconductors for future spin-based electronics or spintronics.
If you are wondering what makes this special, spintronics promise little-to-no standby leakage, low power consumption, amazing endurance, great read-write performances, all in a nonvolatile package, and is said to easily integrate with current CMOS-based electronic circuits. Spin-based magnetoresistive RAM (MRAM) is also a universal memory candidate.
Source: Institute of Science Tokyo, AIP Publishing