Traditional memory devices have limitations, especially as technology gets smaller and faster. Magnetoresistive random-access memory (MRAM) is a game-changer in data storage. Unlike traditional memory, MRAM retains data even when powered off (non-volatile). However, writing data to MRAM usually requires significant power. In this case, scientists are constantly searching for more efficient ways to do this. Surprisingly, the area of research involves using electric fields to control data storage, drastically reducing the energy needed.
The Challenge of Efficient Data Writing
Early MRAM used Oersted fields to switch the magnetization vectors in magnetic tunnel junctions (MTJs) – the tiny switches that store data. However, this method became less efficient as MRAM devices shrunk. Subsequently, spin-transfer torque (STT) and spin-orbit torque (SOT) methods emerged, but they still require considerable energy. Indeed, this is where the exciting advancements in electric field control come in.
Multiferroic Heterostructures: The Key to Efficiency
Researchers have explored multiferroic heterostructures, combining ferromagnetic (FM) and piezoelectric materials. These structures allow for magnetoelectric (ME) coupling, meaning an electric field can directly influence the magnetization, enabling the switching of data without requiring large currents. Secondly, this approach promises to reduce energy consumption significantly in Magnetoresistive random-access memory.
A Breakthrough in Magnetoelectric Coupling
Recently, scientists achieved a remarkable breakthrough. By inserting a thin layer of vanadium (V) between Co2FeSi (a ferromagnetic Heusler alloy) and a piezoelectric substrate (PMN-PT), they created a multiferroic heterostructure exhibiting a giant converse magnetoelectric (CME) coupling coefficient. This means a small electric field can induce a large change in magnetization.
Highly Oriented Co2FeSi: The Secret Ingredient
The key to this success lies in the highly oriented growth of the Co2FeSi layer. The vanadium layer acts as a crucial catalyst promoting the growth of the (422) crystal plane of Co2FeSi. This specific orientation enhances the CME effect, resulting in efficient magnetization switching with electricity. This is a significant advancement compared to previous methods using iron (Fe) layers, which resulted in less-efficient magnetization switching.
Non-volatile Binary States: Enabling Practical Applications
Importantly, this new approach achieves a non-volatile binary state at zero electric field. This is essential for practical Magnetoresistive random-access memory, MRAM, applications, as it ensures data is retained even when the electric field is off. The strength of the magnetic anisotropy can be controlled by adjusting the thicknesses of the vanadium and Co2FeSi layers, offering further customizability and optimisation for applications.
The Future of MRAM: Smaller, Faster, More Efficient
Magnetoresistive Random-Access Memory, MRAM, signifies a major step towards highly efficient and energy-saving MRAM. The ability to control magnetization using electric fields opens exciting possibilities for smaller, faster, and more energy-efficient memory devices. Furthermore, this breakthrough opens up a new frontier in the field of spintronics, where both charge and spin are crucial, with potential applications across various fields.
References
Usami, T., Sanada, Y., Fujii, S., Yamada, S., Shiratsuchi, Y., Nakatani, R., & Hamaya, K. (2024). Artificial control of giant converse magnetoelectric effect in spintronic multiferroic heterostructure. Advanced Science. https://doi.org/10.1002/advs.202413566
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