Storage of digital information in conventional hard disks makes use of the spin orientation of magnetic grains made of more than one million atoms, deposited on thin films. The two possible stable orientations of the magnetic moment define the two logical states of a classical bit, “0” or “1”. To increase the storage density, it is needed to reduce the size of this grains below the few nanometers of the present technology. This has pushed forward the study of magnetism at the nanometer scale, the so call nanomagnetism, and the ultimate size limit: the atomic scale.
When the size of the magnetic grains is reduced, the stability of the two configurations used to store the classical bits is also reduced due to thermal fluctuations. This problem may be avoided in laboratory conditions by lowering the temperature. In fact, researchers at IBM Almaden (USA) have recently proved that at sub-Kelvin temperatures, small chains of up to 12 iron atoms deposited on a monolayer of insulating material, can be used as logic bits. However, the disappearance of the magnetic moment in smaller chains, of up to 4 atoms, shows that additional problems, coming from quantum effects, take place when further reducing the size of the magnetic bits.
In a paper recently published in Physical Review Letters (1), Fernando Delgado and Joaquín Fernández-Rossier (FR), researchers at the INL, have examined fundamental limits to the storage of classical bits of information in single magnetic atoms imposed by quantum mechanics. At the atomic scale, spins are quantized and they can present either integer or half-integer values, with totally different properties. In the case of integer spins, the classical picture of two different spin orientations is no longer valid and must be substituted by a quantum mechanical description in term of quantum states. In this new picture, integer spins are in a “linear combinations of the “0” and “1” states, without a classical counterpart. In other words, integer spins tend to lie in states where its magnetization orientation can be found equally in its “0” and “1” states. This is a manifestation of its quantum nature, as it happens to the Schrödinger cat, which can be in a combination of its live and death states. The INL researchers have proved that this quantum effect does not allow reading or storing logical information in the magnetization orientation of integer spins. Nevertheless, in the case of half-integer spins there are two degenerate stable states, which can be associated to the “0” and “1” logical states, which makes possible the readout and storage of the logical information.
A second quantum effect may prevent the readout: quantum objects are sensitive to the measurement process through the induced back-action. Whenever a meter interacts with a quantum system, it strongly perturbs the original state, demolishing the stored information. The FR paper discusses the conditions of voltage and temperature under which the measurement of a single atomic scale can be done through its magnetoresistance without perturbing its initial state, realizing a quantum non-demolition measurement.
Category Archives: Nano-News
Quantum limits to the magnetic storage of classical information
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INL’ers WANTED!! See the latest nanotechnology job offers
The International Iberian Nanotechnology Laboratory (INL) seeks a highly-qualified, self-motivated postdoctoral researcher to participate in the research of the MEMS and Micro Energy Harvesting Devices group.
The Group of MEMS and Micro Energy Harvesting Devices of INL welcomes applicants with previous experience in cleanroom processing of spintronic sensors/elements (spin valve sensors, magnetic tunnel junctions, permanent micromagnets, flux guides, …) combined with MEMS technology (in- and out-plane actuators, microresonators, and related) and testing of microsystems.
This project will be developed in collaboration with the Spintronics group at INL and other international research groups, which will work on the footprint optimization of MEMS accelerometers using magnetic sensors, sub-micron resolved magnetic imaging scanning platforms, and ultra-sensitive magnetic detectors enhanced by MEMS devices.
The successful candidate must hold a PhD degree in Physics, Materials Engineering, Electronics or related, possess excellent communications in English and a good track-record for disseminating results to the scientific community. Candidates with additional know-how on electronics and hands-on experience with CMOS design will be preferred.
In addition to the opportunity to access the state-of-the-art facilities and work in a multidisciplinary environment, INL will offer the successful candidate an exciting and highly competitive research environment, including salaries in line with those offered by other international research organisations, and a comprehensive fringe benefit package. Researchers at INL will benefit from the various social facilities available at INL, including the INL nursery. The position is for 2 years. Interested applicants should submit their curriculum vitae (with a full list of publications) and a cover letter describing their research experience and the contact details of two referees.
Enquires about the position should be directed to reo(at)inl.int.
INL firmly adheres to a principle of non-discrimination.
DEADLINE: 20-05-2012 (23:00 Lisbon time)
INL’ers WANTED!! See the latest nanotechnology job offers
The International Iberian Nanotechnology Laboratory (INL), based in Braga (Portugal), is the first fully international research organisation in Europe in the field of nanoscience and nanotechnology. INL is currently seeking candidates for two Research fellow positions:
• The first candidate will participate in the research of the Biophotonics group on “light modulation of protein function and cellular metabolism”. Specifically, INL is seeking a Cellular biologist with experience in biophysics/Cellular microscopy.
Click in the following link for more information:
PD4-TP-2012 – Cellular biology and biophysics/Cellular microscopy
• The second position seeks a researcher with previous laboratory experience in processing state-of-the-art PZT materials, cleanroom fabrication and testing of microsystems to participate in the research of the MEMS and Micro Energy Harvesting Devices group.
Click in the following link for more information:
PD7-JG-2012 – Energy Harvesting Micro and Nano Devices
In addition to the opportunity to access the state-of-the-art facilities and work in a multidisciplinary environment, INL will offer the successful candidate an exciting and highly competitive research environment, including salaries in line with those offered by other international research organisations, and a comprehensive fringe benefit package. Interested applicants should submit their curriculum vitae (with a full list of publications) and a cover letter describing their research experience and the contact details of two referees.
More information at: http://inl.int/job_offers
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