Increase memory density with nanowires

US physicists have announced a new technique that allows us to jump one step further in the use of magnetic nanowires for high-density information storage devices.

This technique involves moving magnetic domain walls - separations between two domains from one side to another - along a nanowire by using extremely small polarization current density compared to techniques. before. The researchers claim that this step could yield a new type of magnetic memory with hundreds of times more storage density than current RAM (According to Science 315 1553).

Magnetic domain walls are a narrow boundary between two consecutive magnetic domains, which have magnetized vectors that are oriented in two different directions. Domain walls can move in materials by placing an external magnetic field or injecting a spin-polarized current. Some physicists have calculated that this motion can be exploited in "racetrack" memory, which can store data with much greater density than current RAM.

In a racetrack memory, data is stored in a sequence of magnetic domains - separated by domain walls, along a nanowire (pictured). The individual bits are stored and retrieved by moving these sequences along the nanowires and cutting across the reader and recorder.

If this technology is successful, a feasible method is to use spin-polarized currents to move the domain walls in the nanowires. And the main challenge is how to reduce the current density so small that it is possible to move the domain wall when they are dampened by the defects in the wire. Currently, the required current density is too large for commercial memory.

But recently, Stuart Parkin and colleagues at IBM Almaden Research Center (USA) have found a way to reduce the polarization current density by more than 5 times by exploiting the characteristic of having oscillating frequencies own of the blocked domains. When giving a series of current pulses with appropriate pulse and pulse widths, the amplitude of oscillation increases until the domain wall overcomes the defect itself and moves along the wire.

Necessary pulses are about nanoseconds and Parkin told PhysicsWen that this pulse can easily be used in a tracetrack memory - in fact, a similar pulse has been commonly used in other memory devices.

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