Final Activity Report Summary - EPRMCDSHPANDSIMSOFT (Determination of spin-Hamiltonian parameters of transition metal cages by EPR and MCD and development of associated simulation software)
The fundamental objectives of this research project is the development of a theoretical methodology for the interpretation of the magnetic and magneto-optical properties of polymetallic transition metal cages in which the constitutive paramagnetic ions present magnetic interactions. Such molecular systems have been shown to display superparamagnetic behaviour at low temperatures, meaning that they can be used as the physical support for the development of materials for information storage at the molecular level in form of spin polarisation. Such molecules have been termed Single Molecule Magnets.
The development of such materials requires the detailed understanding, at the molecular level, of the relationship between structure and magnetic properties. The phenomenological interpretation of the magnetic properties of such systems is most commonly done by use of a spin-Hamiltonian model. The relevant spin-Hamiltonian parameters are determined by numerical matrix diagonalisation of the spin-Hamiltonian of the studied system. However in many cases the spin-Hamiltonian matrix of the studied system is of too big dimension to be treated by conventional matrix diagonalisation algorithms with realistic computational time and memory storage requirements.
We have developed a numerical diagonalisation algorithm that allows to numerically diagonalise spin-Hamiltonian matrices of dimensions of the order of 105 to 106 within just few hours the computation being performed on a performant but nevertheless ordinary modern workstation. Then the spin-Hamiltonian terms are transformed by a unitary transformation to the eigen-basis of a given number of low-lying eigenvectors of the system.
We have applied the above theoretical methodology for the interpretation of thermodynamic and spectroscopic properties of various polymetallic transition metal cages. We have shown that in the case that the single-ion second order anisotropy is of the same order of magnitude as the isotropic exchange in the system, a breakdown of the strong exchange limit approximation is observed.
Finally we have observed by 'magneto-circular dichroism' (MCD) the slow relaxation of the magnetisation on a frozen solution of an hexanuclear Mn(III) cage. This observation proves that the observed slow relaxation of the magnetisation is of molecular origin. Such an effect has only once been previously observed by MCD studies on a dodecanuclear mixed valence Mn cage, widely known as Mn12.
The development of such materials requires the detailed understanding, at the molecular level, of the relationship between structure and magnetic properties. The phenomenological interpretation of the magnetic properties of such systems is most commonly done by use of a spin-Hamiltonian model. The relevant spin-Hamiltonian parameters are determined by numerical matrix diagonalisation of the spin-Hamiltonian of the studied system. However in many cases the spin-Hamiltonian matrix of the studied system is of too big dimension to be treated by conventional matrix diagonalisation algorithms with realistic computational time and memory storage requirements.
We have developed a numerical diagonalisation algorithm that allows to numerically diagonalise spin-Hamiltonian matrices of dimensions of the order of 105 to 106 within just few hours the computation being performed on a performant but nevertheless ordinary modern workstation. Then the spin-Hamiltonian terms are transformed by a unitary transformation to the eigen-basis of a given number of low-lying eigenvectors of the system.
We have applied the above theoretical methodology for the interpretation of thermodynamic and spectroscopic properties of various polymetallic transition metal cages. We have shown that in the case that the single-ion second order anisotropy is of the same order of magnitude as the isotropic exchange in the system, a breakdown of the strong exchange limit approximation is observed.
Finally we have observed by 'magneto-circular dichroism' (MCD) the slow relaxation of the magnetisation on a frozen solution of an hexanuclear Mn(III) cage. This observation proves that the observed slow relaxation of the magnetisation is of molecular origin. Such an effect has only once been previously observed by MCD studies on a dodecanuclear mixed valence Mn cage, widely known as Mn12.