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1

Magnetic properties of La0.7Sr0.3Mn0.85Nb0.15-xMgxO3 system

100%

Troyanchuk I. , Tereshko N. , Bushinsky M. , Fedotova V. , Partyka J.

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tom R. 92, nr 1

148--150

EN

Structural and magnetization measurements have been performed on the La0.7Sr0.3Mn0.85Nb5+ 0.15-xMg2+ xO3 system. With rise of the Mg2+ content the formal oxidation state manganese increases from +3 (x=0) up to +3.55 (x=0.15). The substitution of Nb5+ with Mg2+ leads to a gradual weakening of the ferromagnetic component while in the x=0.15 compound A-type antiferromagnetic short-range order is stabilized in spite of macroscopic R-3c symmetry. It is suggested that ferromagnetism is originated from superexchange interactions via oxygen.

PL

Przeprowadzono pomiary strukturalne i namagnesowania układu La0.7Sr0.3Mn0.85Nb5+ 0.15-xMg2+ xO3.Wraz ze wzrostem zawartości Mg2+formalny stopień utlenienia manganu wzrasta z +3 (x=0) aż do +3.55 (x=0.15). Zastąpienie Nb5+ poprzez Mg2+prowadzi do stopniowego osłabienia składnika ferromagnetycznego podczas gdy w związku x=0.15 typu A antyferromagnetyczny porządek krótkiego zasięgu jest ustabilizowany pomimo makroskopowej symetrii R-3c. Sugeruje się, że ferromagnetyzm pochodzi z nadwymiany za pomocą tlenu.

2

Multiple electron exchange in calculations of pairwise nonadditive contribution to trimer interaction energy

72%

Lotrich V. F. , Szalewicz K. , Jeziorski B.

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tom Vol. 72, nr 7S

1826-1848

EN

The first order of the symmetry-adapted perturbation theory has been used to compute the pairwise nonadditive contribution to the exchange repulsion energy in the He3, Ne3, Ar2HF, and (H2O)3 trimers. The contributions from single and double electron exchanges, as well as from the cyclic permutations involving three electrons at a time, were calculated seprately and compared with the accurate result involving all possible electron permutations. The intramonomer electron correlation was completely neglected and the Hartree-Fock determinants were used to represent the monomer wave functions. The importance of the resulting three-body contributions, which can be quadratic (single exchanges), cubic (three-electron cycles), and quartic (double exchanges) in a typical intermolecular overlap integral S, is studied for several geomertical configurations of the investigated systems. Whereas the S(2) and S(3) terms are important for all systems, the role of the S(4) terms turns out to be very small for Ar2HF, large for the rare-gas timers at linear configurations, and appreciable for the water trimer. The higher than double exchanges (S(5) and higher terms) are negligible for all systems except for the water trimer at very small intermonomer separations where the expansion in powers of S ceases to be useful. The nonadditivity of the so-called zeroth-order exchange energy, i.e., the difference between the Heitler-London and the first-order energies, has also been investigated. The zeroth-order exchange energy contains only the S(4) and higher terms and becomes significant when the S(4) contribution to the first-order energy is important. The S(2) and S(3) contributions to the first-order exchange nonadditivity in the Ar2HF trimer agree well with the calculations of Cybulski and collaborators[J. Chem. Phys. 101, 10708 (1994), ibid., 106, 3301 (1997)] using their pseudo-dimer model.

3

Vibronic behaviour of octahedral Cu(II) complexes in Cu(2-benzoylpyridine)2(NO3)2x2H2O crystal with a weak superexchange coupling. Temperature EPR studies

72%

Hoffmann S. K. , Goslar J. , Hilczer W. , Goher M. A. S.

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2000

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tom Vol. 48, No. 4

397-409

EN

Octahedral [Cu(2-benzoylpyridine)2 (H20)2] complexes in the Cu(2-Bzpy)2-(NO3)2 .2H2O are very dynamical and Cu(II) ions are very weakly coupled as it is shown by the single crystal EPR measurements in the temperature range 4.2-300 K. Rigid lattice limit (9 K) of spin-Hamiltonian parameters are: gx = 2.137, gy = 2.014, gz = 2.306 as determined by decoupling of exchange merged EPR lines. The ground state is predominantly Ix(2) -y(2)) with 8% of the Iz(2)) state. This mixing is produced by zero-point motions in the ground vibrational state and results in g x > gy with strong lowering of the gy-value. The decoupling procedure gave superexchange coupling parameter J = 0.0040 cm(1), which unexpectedly is temperature independent in contrast to other weakly coupled Cu(II) paramagnets. The g-factors show relatively strong temperature variations with gy practically not affected by temperature and a tendency to averaging of the g x and gz with room tem-perature parameters: g x = 2.161, gy = 2.013, gz = 2.285. This is explained as the pseudo Jahn-1eller effect with dynamical transitions between two elongated octahedral axes, i.e. O-Cu-O (x-axis) and H2O-Cu-H2O (z-axis) with N-Cu-N (y-axis) direction ill the in-plane coordination with pyridine nitrogen not affected by vibronic dynamics. The vibronic effect can be described by two-well model in the temperature range 80-150 K only with energy difference between the ground vibronic state in the well being 220 cm-l. At lower temperatures Cu(II) complexes are strongly localized in the deepest potential well, whereas at higher temperatures, the vibronic g-factor averaging is dominated by the other mechanism.

4

Magnetic and magnetotransport properties of nickel-doped manganites

72%

Troyanchuk I. , Tereshko N. , Bushinsky M. , Fedotova V. , Świć A. , Koltunowicz T. N.

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tom R. 94, nr 4

126--129

EN

Structural and magnetization measurements have been performed on the La1-xSrxMn0.5Ni0.5O3 (0 ≤ x ≤ 0.2) with perovskite structure. Structural data testify a partial order of the Ni and Mn ions in all the compounds in spite of chemical substitution of the La3+ ions by Sr2+ ones and an increase of the oxidation state of the Ni ions from 2+ towards to 3+ one. Magnetic structure of the compounds changes from ferromagnetic one to antiferromagnetic (compounds with x ≥ 0.1) while the temperature of a transition into paramagnetic state remains about 270 K for all the samples.

PL

Wykonano strukturalne i magnetyzacyjne pomiary na La1-xSrxMn0.5Ni0.5O3 (0 ≤ x ≤ 0.2) ze strukturą perwoskitu. Dane strukturalne potwierdzają częściowe uporządkowanie jonów Ni i Mn we wszystkich związkach pomimo chemicznej substytucji jonów La3+przez jony Sr2+ oraz zwiększenia stanu utlenienia jonów Ni od 2+ do 3+. Struktura magnetyczna związków zmienia się ze stanu ferromagnetycznego do antyferromagnetycznego (związki o x≥ 0.1), podczas gdy temperatura przejścia w stan paramagnetyczny pozostaje w przybliżeniu stał dla wyrzyskich próbek i wynosi 270 K.