Category Archives: Nano-Electronics

Quantum limits to the magnetic storage of classical information


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 In the case of integer spins, the classical picture of two different spin orientations is no longer valid and must be substituted by a quantum mechanical description in term of quantum states.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.

The “Rule-of-Three”. Admatechs Company Limited (Japan)

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Within this section, Nanobugle will test the 3 main key success factors for the development of new nanotechnology/nanoscience companies.



This week: Japan



1) How was the company born?

Admatechs Company Limited was established in February 1990, jointly by Toyota Motor Corporation and Shin-Etsu Chemical Corporation Limited.

The company name “Admatechs”, is created by combining the initial characters from the company concept “Advanced Material Technologies.”

Admatechs develops advanced materials. The company’s R&D Division is developing several technologies based on VMC combustion technology, for example, coarse particle removal from spherical metal oxide particles, particle surface treatment, and high dispersion of particles.

2) Added value of the products/services

ADMAFINE is the main product developed by Admatechs. It consists of microscopic spherical oxide particles produced by oxidizing metal powders using an original technique known as the VMC method.

The highly specific functionality of spherical particles is used in various fields, including computers, electrical and electronic products, automobiles, foods, and medical equipment. Product examples include, adhesive that optimizes heat conductivity and heat resistance, liquid resin featuring high fluidity and rigidity, and functional paints where heat and weather resistance is required. Each of the ADMAFINE particles maximizes the function of these products and improves the characteristics of the product.

3) Business Strategy

Future business strategy at Admatechs is based in Research and Development. The R&D Division of Admatechs is developing several technologies based on VMC combustion technology, for example, coarse particle removal from spherical metal oxide particles, particle surface treatment, and high dispersion of particles. The company is engaged in a variety of research and development, including basic research to evaluate the rheologic properties of ADMAFINE, applied research, and other research for production engineering.

More information:

Takeshy Yanagihara

Sales and Marketing Development

Admatechs Company Limited

Aichi, Japan



Reading information from the smallest magnetic objects

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Digital information can be stored in tiny magnets known as nanomagnets. Miniaturization increases the density of stored information, but also makes it harder to read.  The smallest magnet that can be conceived is that of the nuclear spin of a single atom.

In an article recently published in “Physical Review Letters”, scientists at the INL (International Nanotechnology Laboratory) have presented computational simulations that show how a single nuclear spin can be detected by passing a small electrical current through it.   According to Joaquin Fernandez Rossier, leader of the project: “we find that the indirect coupling between the current electron and the nucleus leads to extra features in the current that can be resolved with state of the art experimental set-ups. This method is completely different from conventional magnetic resonance techniques that can only access the information from ensembles of at least trillions of atoms.”

For the experimental confirmation, they are considering two different systems; a Manganese atom absorbed on an atomically thin insulating surface probed with an atomic-resolution tip (scanning tunneling microscopy), and a single Bismuth dopant in a Silicon nanotransistor. “Our simulations demonstrate that this technique yields information about the occupations of the nuclear spin states, paving the way towards transport-detected single nuclear spin resonance” Dr. Fernández said.

The image represents one of the systems described in the paper:  the atom whose nuclear spin is probed (shown in magneta) sits on a surface (the blue atoms). The reading tool is a Scanning Tunneling Microscope (grey atoms in the figure)