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Multi State Memory in Artificial Multiferroics

Periodic Reporting for period 1 - MuStMAM (Multi State Memory in Artificial Multiferroics)

Reporting period: 2018-03-01 to 2020-02-29

In this project, the present challenge to increase the areal density of computer memory storage was addressed by multiferroic tunnel junction (MFTJ) based multi-state memory device. The fellow was able to create a heterostructure with possible multi-state switching originating from magnetic switching, ferroelectric switching, and exchange bias switching at the same memory cell. The fellow also investigated the possibility of room temperature ferromagnetic multiferroic material by vertically aligned nanocomposite film for next-generation multistate memory and electric control of magnetism.

Electricity use by ICT could exceed ~21% (expected) to 50% (worst-case) of the global total electricity in 2030 compared to 2018. Only the data centres will use one-third of that which is more than the national energy consumption of many countries. That puts ICT’s carbon footprint to go up to almost 10 times by 2030. With the spectre of energy-hungry data-driven alarming future looming, new technology is very much essential to keep the industry’s environmental impact low while fulfilling the consumer demand for high-speed and high-density data. The results achieved in this project are very important for the society as the society is facing the mammoth challenges to create energy-efficient high-density memory.

The overall objectives of this project were to understand the strongly correlated oxide materials and their nanostructures for spintronics based multi-state non-volatile memory. Spintronics is promising for device applications but complicated by materials science aspects such as growth, characterisation and materials physics which is required to be properly investigated in order to perform with low power and higher efficiency. The project addressed these as proposed.
The fellow investigated different materials systems to investigate possible multi-state memory in a single memory cell. Two different approaches were taken. In the first approach, the fellow investigated heterostructure of strongly correlated oxide materials such as La0.7Sr0.3MnO3 (LSMO) and BaTiO3 (BTO) for independent magnetic and electrical switching from ferromagnetic LSMO and ferroelectric BTO respectively. An exchange bias (EB) coupling was also observed at the interface of LSMO and BTO which could also be switched. In the second approach, the fellow investigated room temperature ferromagnetic multiferroic materials. By using the concept of 3D strain engineering in vertically aligned nanocomposite thin film the magnetic structure of the materials in multiferroic perovskite was changed. Room-temperature ferroelectricity and high-temperature ferromagnetism (TC~90K) was observed in o-RMnO3 material: SmMnO3.
Exploitation and dissemination: The results obtained in the project have been published in reputed peer-reviewed journals like Nature Communications and ACS Applied Materials and Interfaces. The fellow has attended international conferences and workshops such as IWAM-2019, presented the results, and meet both young and renounced experienced researchers. The fellow also presents the results in the department of the University of Cambridge every semester.
The fellow received outstanding results from the project. The exchange bias coupling was created at the interface of ultra-thin (<5 unit cell) ferroelectric BTO and ferromagnetic LSMO without any conventional antiferromagnetic material, which is very novel. By XMCD measurement at the Diamond Light Source, UK it was confirmed that the Ti of BTO possesses magnetism at such a fully strained interface of LSMO and BTO. Further, by vertically aligned nanocomposite film the fellow was able to increase ferromagnetic and ferroelectric transition temperature, which is a novel way to manipulate functionalities of multiferroic materials and create room-temperature ferromagnetic multiferroics film. The results achieved and knowledge gained during the project is important steps forward to use these materials systems for energy-efficient ICT applications such as non-volatile memory. The fellow presented the results in front of young and established researchers at the University of Cambridge and other world renounced institute/conferences. This will increase the awareness of the need for energy-efficient ICT thus create a socio-economic impact.
Exchange bias at LSMO-BTO interface
Room temperature ferroelectricity in SMO VAN film