The nature of the ferromagnetic ground state in the Mn4 molecular magnet

Using ab initio band structure and model calculations we studied magnetic properties of one of the Mn$_4$ molecular magnets (Mn4(hmp)6), where two types of the Mn ions exist: Mn3+ and Mn2+. The direct calculation of the exchange constants in the GGA+U approximation shows that in contrast to a common belief the strongest exchange coupling is not between two Mn3+ ions (J_{bb}), but along two out of four exchange paths connecting Mn3+ and Mn2+ ions (J_{wb}). The microscopic analysis performed within the perturbation theory allowed to establish the mechanism for this largest ferromagnetic exchange constant. The charge ordering of the Mn ions results in the situation when the energy of the excited state in the exchange process is defined not by the large on-site Coulomb repulsion U, but by much smaller energy V, which stabilizes the charge ordered state. Together with strong Hund's rule coupling and specific orbital order this leads to a large ferromagnetic exchange interaction for two out of four Mn2+ --Mn3+ pairs.Comment: 12 pages, 10 figure

Calculation of the behaviour of hydrogen in arc discharge

Translated from Russian (Report of the E.O. Paton Electric Welding Inst., Kiev, 1998)Available from British Library Document Supply Centre-DSC:9023.190(VR-Trans--9084)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Role of temperature in hydrogen-induced cracking of structural steels and welded joints

Translated from Ukrainian (Avtom. Svarka 2000 (1) p. 2-7)Available from British Library Document Supply Centre-DSC:9023.190(10438)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Ovarian sarcomas: a review of literature

The review describes the etiology and clinical features of ovarian sarcomas and current approaches applied to their diagnosis and treatment

The Conducting Spin-Crossover Compound Combining Fe(II) Cation Complex with TCNQ in a Fractional Reduction State

The radical anion salt [Fe­{HC­(pz)₃}₂]­(TCNQ)₃ demonstrates conductivity and spin-crossover (SCO) transition associated with Fe­(II) complex cation subsystem. It was synthesized and structurally characterized at temperatures 100, 300, 400, and 450 K. The compound demonstrates unusual for 7,7,8,8,-tetracyanoquinodimethane (TCNQ)-based salts quasi-two-dimensional conductivity. Pronounced changes of the in-plane direct-current resistivity and intensity of the electron paramagnetic resonance (EPR) signal, originated from TCNQ subsystem, precede the SCO transition at the midpoint <i>T</i>* = 445 K. The boltzmannian growth of the total magnetic response and structural changes in the vicinity of <i>T</i>* uniquely show that half [Fe­{HC­(pz)₃}₂] cations exist in high-spin state. Robust broadening of the EPR signal triggered by the SCO transition is interpreted in terms of cross relaxation between the TCNQ and Fe­(II) spin subsystems