Magnetic Properties Changed by Electric Current Alone Without Altering Materials... Next-Generation Memory Technology Advances [Reading Science]

DGIST Lowers Ferrimagnetic Material's Compensation Temperature by Up to 110K
Spin Arrangement Controlled with Current Pulses, No Need for Chemical Processing or Thickness Adjustment

A technology has been developed that enables control of a material's magnetic properties solely with electric current, without changing the composition or thickness of the material. Since the magnetic characteristics of specific regions can be electrically modified even after device fabrication, this is expected to contribute to the development of next-generation spintronics memory.

DGIST announced on September 15 that the research team led by Professor Jeongil Hong of the Department of Chemical Physics has succeeded in lowering the 'compensation temperature' by as much as approximately 110K (kelvin, corresponding to a change of 110 degrees Celsius) by changing the spin arrangement inside a ferrimagnetic material using current pulses.

The principle of controlling the CoGd spin arrangement and compensation temperature with electric current. When current flows through Pt, the spin arrangements of IrMn₃ and CoGd change, forming a helical structure. As the current increases, the compensation temperature decreases. Provided by the research team

Ferrimagnetic materials are substances in which two types of magnetism, oriented in opposite directions, coexist. The magnitude of each magnetization varies depending on temperature, and at a certain point, the two cancel each other out—this point is called the compensation temperature. Near this temperature, magnetization can be controlled rapidly and efficiently, making it a crucial property for developing high-speed, high-density memory devices.

Traditionally, adjusting the compensation temperature required processes such as modifying alloy composition, changing the thickness of thin films, annealing, or ion implantation. For this reason, it has been difficult to selectively control the magnetic properties of certain areas after device fabrication, and these additional processes could alter the structure or composition of the material itself.

Current Alters Spin Arrangement... Compensation Temperature Shifted by Up to 110K

The research team used a multilayer thin film structured with platinum (Pt), iridium manganese (IrMn₃), and cobalt gadolinium (CoGd) stacked sequentially. When current flows through the platinum layer, spin–orbit torque is generated by electron spin, which then changes the spin arrangement of the adjacent iridium manganese.

This altered spin state in iridium manganese subsequently affects the spins within the cobalt gadolinium layer. The research team confirmed that iridium manganese forms a strong coupling with cobalt (Co) spins but almost no coupling with gadolinium (Gd) spins. As a result, within the multilayer thin film, the spin direction gradually varies depending on the thickness, leading to changes in the magnetic interaction between cobalt and gadolinium, and ultimately lowering the compensation temperature.

Experimental results showed that the compensation temperature of a film with equal ratios of cobalt and gadolinium (Co?.?Gd?.?) decreased from about 350~360K to about 280~290K—around a 70K drop—after applying current pulses. In thin films with a higher cobalt ratio (Co?.??Gd?.₃₂), the compensation temperature decreased from around 170~180K to 60~70K, resulting in a maximum shift of about 110K.

The team also confirmed that increasing the amplitude or duration of current pulses gradually reduced the compensation temperature. This means that magnetic properties can be tuned using only electrical signals applied at room temperature, without the need for external magnetic fields or additional chemical treatments.

Photo of the research team. From the left, Professor Hong Jeongil of the Department of Chemistry and Physics at DGIST, Dr. Choi Wonchang, Postdoctoral Researcher, and Sim Taebo, Integrated Program Student. Provided by DGIST

The research team expects that this technology can be used to set different magnetic properties at different locations within a single thin film or to electrically control the operating temperature of devices.

Professor Hong stated, "This result demonstrates that the magnetic properties of materials can change significantly not only depending on the types of atoms and their spatial arrangement, but also on the internal spin configuration. The ability to control the compensation temperature by adjusting the intensity and duration of current pulses presents great potential for developing next-generation spin memory technology capable of realizing different magnetic properties at specific locations."

Wanchang Choi and Taebo Shim participated as co-first authors in this research. The research results were published on July 31 in the international journal Advanced Functional Materials.

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