Spinhenge@home

WU Information: Workunit "Core / shell nanoparticle" from April 09, 2011

Fri, 08 Apr 2011 22:00:00 GMT

The interest of the scientific community in the magnetism of nanoparticles is strongly related to their potential application in high density data storage and spin electronics devices. Furthermore, fundamental questions are still opened to understand the static and dynamic aspects of the magnetic behavior of so-called core/shell nanoparticles.
As shown in the figure below, in such systems two different metals are arranged in a way that one metal is forming the core (red) of the nanoparticle and is seperated from the shell (yellow) which consists of a different metal. In between there is an interface layer where both kinds of metal interact. We assume an antiferromagnetic coupling within the core and a ferromagnetic coupling within the shell. Furthermore, the interfacial spins are coupled by a weak ferromagnetic coupling. We want to study a rather small nanoparticle which nevertheless consists of 32565 spins in total! For such a "monster calculation" we need the help of all spinhenge users! Core/Shell nanoparticle consisting of 32565 spins. The core spins (shown in red) are made of a different metal than the shell spins (shown in yellow).

WU Information: Workunit "Fe30_map" from January 27, 2007

Fri, 26 Jan 2007 23:00:00 GMT

In recent careful magnetic measurements of the Fe30 molecule done at the Ames Laboratory we have observed some strange features which could not have been detected before due to the sophisticated technique that one needs have at hand to perform such measurements. In order to understand these features we have proposed a new model description which takes into account small deviations from the ideal icosidodecahedron structure of the molecule and maps these onto the intra-molecular interaction scenario.
However, there is one unknown parameter which needs to be determined by subsequent comparison with the experimental data. In order to do so we need to perform a huge number of similar simulations which will be evaluated automatically and compared with the experiment! Using Spinhenge@home we distribute the whole calculation using several million work units! Our goal is to understand the reason for strange features recently detected in magnetic measurements of Fe30.

WU Information: Workunit "SC lattice" from December 22, 2006

Thu, 21 Dec 2006 23:00:00 GMT

29791 spins arranged on a three dimensional so-called SC lattice. Here, SC means "simple cubic" with the property that each spin (yellow sphere) is interacting with its 6 nearest neighbors (red spheres). The figure on the right-hand side shows the SC unit cell in detail. The whole 3D structure is build of these little unit cells. To see the relation between the 3D structure and the unit cell just look at the grey sphere which is connected to the 3 next neighboring spins of that unit cell and to the 3 neighboring spins of 3 other unit cells adjacent to it.
With this calculation we want to test the efficiency of a new Monte Carlo routine and calculate the critical temperature of a large magnetic system. To do so we have to perform 250.000 Monte Carlo steps per temperature value ranging from 1 to 1000 Kelvin. Using Spinhenge@home we can distribute the whole calculation using more than 150.000 work units.

WU Information: Workunit "BCC lattice" from December 13, 2006

Tue, 12 Dec 2006 23:00:00 GMT

9261 spins arranged on a three dimensional so-called BCC lattice. Here, BCC means "body centered cubic" with the property that each spin (yellow sphere) is interacting with its 8 nearest neighbors (red spheres).
With this calculation we want to test the efficiency new Monte Carlo routine and calculate the critical temperature of a large magnetic system. To do so we have to perform 1000000 Monte Carlo steps per temperature value ranging from 1 to 1000 Kelvin. Using "Spinhenge@home" we can distribute the whole calculation using more than 100000 work units.

WU Information: Workunit "Magnetic great rhombicosidodecahedron" from December 05, 2006

Mon, 04 Dec 2006 23:00:00 GMT

With this calculation we want to find out the magnetic properties of an artificial magnetic molecule which is composed of 120 spins located on the vertices of a so-called great rhombicosidodecahedron. This structure is the largest of all Archimedean solids! The great rhombicosidodecahedron is composed of squares, hexagons, and decagons. Here, we study the antiferromagnetic version and want to find out its magnetic properties. We have to perform some very low temperature simulation in order to find unusual behavior like phase transitions. To do so we have to do 1.0000.000 Monte Carlo steps per field value to get the necessary accuracy! There are two series with different magnetic fields. Using Spinhenge@home we distribute the whole calculation using more than 30.000 work units. Which is equal to more than 90.000 results which were sent out. We send out two different series of this with a different magnetic field. One will be calculated by T=25 and the other by T=30.
120 paramagnetic Fe3+ ions (S = 5/2) embedded on the vertices of a great rhombicosidodecahedron - The largest of all Archimedean solids!

WU Information: Workunit "Magnetic Fullerene" from November 05, 2006

Sat, 04 Nov 2006 23:00:00 GMT

With this calculation we want to find out the magnetic properties of an artificial magnetic molecule which is composed of 60 spins located on the vertices of a truncated icosahedron. Such a structure is known to almost everybody as it is the polyhedron which is the blueprint for a soccer ball! Moreover, in 1985 this structure has become very famous and it still is. Curl, Kroto, and Smalley (they later got the Nobel price for Chemistry for their findings) found that carbon can not only exist as graphite and diamond, but also exists in a stable form as the Fullerene C60! The Fullerene is perfectly symmetric and composed of just pentagons. Here, we study the antiferromagnetic version and want to find out its magnetic properties. We have to perform a very low temperature simulation in order to find unusual behavior like phase transitions. To do so we have to do 10.000.000 Monte Carlo steps per field value to get the necessary accuracy! Using Spinhenge@home we distribute the whole calculation using more than 100.000 work units.
60 paramagnetic Fe3+ ions (S = 5/2) embedded on the vertices of a truncated icosahedron - or soccer ball (also named "Fullerene" or "Buckyball" after the famous architect Richard Buckminster Fuller).

WU Information: Workunit fe30_20x20_fine from October 26, 2006

Wed, 25 Oct 2006 22:00:00 GMT

This is a similar project like the fe30_20x20. By this WUs the total monte carlo cycles increased to find better conditions. This one can be charged with the old ones. So we get a better result over all.
{Mo72Fe30}* "balls" arranged on a square lattice ball-to-ball distance shrinks during synthesis process Formation of additional oxygen bridges which connect each ball with its 4 nearest neighbors. Susceptibility measurements suggest a strong antiferromagnetic ball-to-ball interaction!

WU Information: Workunit Fe30_dip_structure from September 20, 2006

Tue, 19 Sep 2006 22:00:00 GMT

With this calculation we want to trace the fine structure of the susceptibility change in the Fe30 molecule when it is subject to an external magnetic field at very low temperatures. It has been found that at about 1/3 of the saturation field, which is the field where all spins are aligned parallel to the external field, a sharp resonance like anomaly appears. One can show that this anomaly is caused by the existence of 2 different types of spin configurations which become energetically competitive at 1/3 of the saturation field. However, it is totally unknown how the resonance looks like for very low temperatures and until now nobody has performed such calculations since they are very time consuming! One has to perform 3.000.000 Monte Carlo steps per field and temperature value to get the necessary accuracy! Using Spinhenge@home we distribute the whole calculation using more than 30000 work units. Our goal is to learn more about the "energy landscape" of that system at 1/3 of the saturation field for further investigations.
Exploring the fine structure of the "resonance" at 1/3 of the saturation field:

WU Information: Workunit kagome_2 from September 12, 2006

Mon, 11 Sep 2006 22:00:00 GMT

This project is similarly kagome_100x100. On this occasion, the same qualities become an examined at another temperature and another magnetic field.