Formation of correlated spin systems in one- and two-dimensional copper and lanthanide compounds.

Autor: Yablokov, Yu., Voronkova, V., Legendziewicz, J., Huskowska, E., Oczko, G., Borzechowska, M.
Zdroj: Applied Magnetic Resonance; Jan2000, Vol. 18 Issue 1, p165-176, 12p
Abstrakt: Electron paramagnetic resonance (EPR) of the systems of exchange-coupled ions differing strongly by spin-lattice relaxation times are discussed. The physical description of a rapid process which modulates and averages out the other, more slow one, is extended to the situations when paramagnetic ions participate in several exchange processes. The layered copper-neodymium squarate, [CuNd2(C4O4)4H2O16] · 2H2O (I), and the one-dimensional copper-lanthanide Cl3-acetates, CuLn2× (Cl3CCOO)8 · 6H2O (Ln = Nd3+ (II), Pr3+ (III)), were investigated by X-band EPR in the temperature range 4.2–300 K. These compounds were shown to consist of subunits admitting exchange interaction between Cu ions, Cu-Nd ions and Nd-Nd ions. At high temperatures the short spin-lattice relaxation time of Nd3+ averages out the Cu-Nd exchange interaction. The manifestation of this interaction should be temperature dependent when governed by the spin-lattice relaxation of one of the partners. The collective Cu spin-system exists in I at T > 250 K ( J Cu-Cu≈ 0.1 cm−1) and gradually transforms into Cu-Nd spin-system which dominates at T < 20–30 K ( J Cu-Nd ≈ 0.4 cm−1) with J Cu-Nd > J Cu-Cu > J Nd-Nd ⋅ Polymer chains in II may be considered as weakly interacting asymmetrical triads −Nd1−Cu-Nd2 − (with the largest components of J ij tensor ≈ 0.3 cm−1). For III the lowest state of Pr3+ was proved to be a nonmagnetic singlet with J Cu-Pr equal to zero. Very weak, temperature-dependent exchange interaction between Cu2+ ions via two Pr3+ ions ( J Cu-Cu ≈ 0.015 cm−1 at T = 4.2 K) was observed. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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