| Posted: Jul 26, 2017 |
Hard drive boost comes in layers of iron and cobalt
(Nanowerk News) A*STAR researchers have created a promising new material from thin layers of iron and cobalt that could enable magnetic recording technologies such as hard drives to be boosted with microwaves (Applied Physics Letters, "Co/Fe mulitlayers with ultra-low damping and large negative anisotropy as the free layer for spin torque oscillator").
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Zhou Tiejun, Chung Hong Jing and colleagues at the A*STAR Data Storage Institute fine-tuned both the magnetic properties and the microwave response in their thin layers, creating an ideal material to drive a tiny quantum-powered microwave generator called a spin torque oscillator.
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| Microwaves could boost the speed and energy efficiency of hard drive memory. (Image: egortupikov/RooM/Getty)
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The team had previously studied layers of cobalt and iridium and found a surprising magnetic irregularity — the material strongly preferred having its magnetic field aligned in one particular direction, a property known as magnetic anisotropy (Nanotechnology, "Reduction of magnetic damping and isotropic coercivity and increase of saturation magnetization in Rh-incorporated CoIr system"). With careful alignment of the material, its anisotropy would make it easier to magnetize and demagnetize.
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In this new work, the team found that sandwiching cobalt with iron, instead of iridium, produced stronger magnetic anisotropy and had superior microwave performance.
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Microwaves generated by a spin torque oscillator embedded in the read-write head of a hard drive would make writing the data more energy efficient, Chung said.
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“The microwaves effectively lower the energy barrier for flipping the direction of the magnetic domains,” says Chung.
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The microwave signal would aid the switching of magnetization required to write data to a hard drive by setting the magnetic fields of the atoms in the hard drive weaving in circles, in the same way that a spinning top wobbles in circles, an effect known as precession. The cobalt-iridium stack lost the microwave energy quickly, like a top spinning on a thick carpet, an effect known as damping. However, in the cobalt-iron stack, the damping was much lower, like a top spinning on a hard polished floor.
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The breakthrough came from the team’s work in separately engineering the magnetic and microwave properties of the stack, said Chung.
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“We take a lot of care to achieve the desired interfacial quality of the layers. Control at the nanometer level is utterly important,” he said.
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The team tested more than 30 combinations of materials, first exploring the effect of layer thickness, annealing temperature and sputtering rate and temperature. Finally, they tested them in a full stack configuration, concluding cobalt and iron in equal layers of 0.625 nanometers thickness was optimal.
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Chung says there is much work still to be done to bring this technology to fruition.
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“It’s difficult, because of the complexity of the material design and the challenges of integrating the spin torque oscillator into the magnetic read-write head.”
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The A*STAR-affiliated researchers contributing to this research are from the Data Storage Institute.
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