One of the most promising new memory technologies is magnetic random access memory (MRAM). Their ability to attain exceptionally fast speeds and their non-volatility are their main advantages over traditional computer memories and other upcoming memory architectures. Engineers must be able to thoroughly research the switching trajectories in ferromagnet/antiferromagnet exchange-biased systems in order to enhance the speed and performance of MRAMs. However, there are currently just a few tools available to track these processes across time.
The time-resolved detection of a spin-orbit torque switching of magnetization and exchange bias has recently been performed by researchers from the Technical University of Munich and Tsinghua University. They used an approach described in Nature Electronics that relies on cutting-edge magnetic microscopy equipment. According to Christian Back, one of the study’s authors, “in-depth understanding of the magnetization switching process between “0” and “1” is vital to approaching the greatest writing rates with MRAMs.”
“However, up to now, only quasi-static studies have been able to detect magnetization switching, and neither the timeframes nor the precise writing process have been understood. It was only natural for us to investigate this mechanism in depth since our group specialises in time-resolved magnetic microscopy with high temporal resolution (1 picosecond temporal and about 300 nm spatial resolution).”
Back, Yuyan Wang, and their colleagues’ most recent study expands on a number of earlier investigations where they looked at simpler structures using time-resolved magnetic microscopy methods. They particularly employed a stroboscopic pump-probe in their most recent investigation to track the switching path of a magnetic element. Using this method, they were able to capture a switching process “magnetic movie” with great temporal and spatial resolutions.
Back said, “In our situation, the probing pulse is a laser pulse that allows measurement of the magnetic state, and the pump pulse is a current pulse passed through one of the layers of the prototype MRAM element. “Thus, switching trajectories or whole movies are recorded and contrasted with accurate models of the entire magnetic element. We may now make a definitive claim about the switching process as a whole and ultimately extract the pertinent switching process characteristics.”
The researchers eventually achieved multilevel switching of the magnetization and antiferromagnetic exchange bias on a sub-nanosecond timescale by experimenting with the current pulse’s parameters. These two processes were found to be connected with the formation of multiple domain structures at the antiferromagnetic interface. Additionally, they demonstrated how the multi-level magnetization switching during the brief current pulse could be stabilised by the spin-orbit torque caused switching of exchange bias in their MRAM prototype, boosting the device’s stability.
The examination of the spin dynamics of spin-orbit torque (SOT)-based memory systems with a temporal resolution substantially greater than 100 ps saw tremendous development, according to Back. The scientists “found a multi-level switching mechanism of the magnetization and exchange bias in SOT devices on sub-nanosecond timescales by applying time-resolved magneto-optical Kerr microscopy coupled with micromagnetic simulations.”
The information acquired by Back, Wang, and their colleagues highlights prospective approaches that might provide engineers flexible control over the critical functions underlying MRAM device operation, eventually enhancing their stability. Their work might eventually lead to the creation of SOT-MRAM with multi-bits that can function at ever-increasing speeds, which holds great promise for applications such as neuromorphic computing and in-memory computing.
To further increase their operating speed and lower their power consumption, Back said, “We now want to continue exploring the spin dynamics of the SOT-MRAM devices incorporating new materials (e.g., 2D materials) and unique topologies.”
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