萌妹社区

A 'sandwich' of three iron alloy layers could help to create computer hard drives that can store more data than ever before. Tiejun Zhou and co-workers at the A*STAR Data Storage Institute in Singapore expect that their development, based on a new technology called heat-assisted magnetic recording (HAMR), could boost the capacity of disks.

Conventional hard drives contain a tiny electromagnet鈥攁 write head鈥攖hat hovers over a spinning disk coated with a ferromagnetic material. The electromagnet induces the magnetic field within small regions of the disk to point either up or down, encoding one bit of data.

Heat can jumble these magnetic bits and destroy the data. The latest disks use materials with a very large coercivity鈥攁 measure of how difficult they are to demagnetize. However, write heads must exert even greater magnetic fields to encode data in such materials. The balance between bit size, coercivity and the electromagnet's strength ultimately puts an upper limit on disk density of about 1 terabit per square inch.

In HAMR systems, each recording region is briefly heated above its Curie temperature, a point when magnetic coercivity drops significantly and a much smaller field can write the bit. Once the region cools, the coercivity rises and the bit locks into place.

Zhou's team found a way to reduce both the writing temperature and the switching field in HAMR systems. The upper iron鈥損latinum layer of the sandwich stores data bits; the lower iron鈥揷obalt layer helps to channel the write-head's magnetic field, enabling data writing; and the middle iron鈥搑hodium layer acts as a switch between the two. The middle layer is antiferromagnetic at room temperature so blocks any magnetic coupling between the other layers. At about 350 kelvin, however, it becomes ferromagnetic, allowing the layers to couple.

Iron鈥損latinum normally has a Curie temperature of about 750 kelvin, but that plummets when coupled to the iron鈥揷obalt layer. Data can therefore be written to the iron鈥損latinum layer once the iron鈥搑hodium layer becomes ferromagnetic, at about 350 kelvin.

Coupling also reduces the coercivity of the iron鈥損latinum layer, so a write head would need only to generate one-third of the usual magnetic field to encode a bit. "Theoretically, the bit can occupy a space as small as 100 square nanometers," says Zhou. The team now plans to reduce the size of the nanocrystals in each data region of the iron鈥損latinum layer, while maintaining its high coercivity.