| |
 |
UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-23 18:24 |
 |
|
|
|
Conference: Bucharest University Faculty of Physics 2002 Meeting
Section: Atomic and Molecular Physics; Astrophysics
Title:
ESR of Cu2+ Ions in Binuclear Antiferromagnetic
Copper Acetate Monohydrate
Authors:
V. V. Grecu*, Maria Nicoleta Grecu**
Affiliation:
* Physics Faculty, University of Bucharest,
** National Institute fo Materials Physics, Bucharest
E-mail
Keywords:
Abstract:
In this work we are reporting about a new paramagnetic center in powdered copper acetate. This material has been studied long time ago[1,2]. The interest was determined by its peculiar temperature dependence of the magnetic susceptibility, which continuously decreased by lowering the temperature. This behavior and the EPR results were interpreted by assuming a clustering of two copper ions in a molecular complex [Cu(CH3OO)2.H2O]2. The ground state of this dimer is a singlet state and there is a triplet exited state at 285 cm-1. By lowering the temperature the number of dimers in triplet state decreases exponentially and the magnetization goes to zero. The ESR spectrum of these triplets can be interpreted as an S=1 center with rhombic symmetry [1]. Our data confirm the values reported in literature. One very important thing is the fast decrease of the ESR signal intensity as the temperature is lowered from 185K to 97K.
Besides this triple state center another new center is observed. It is a paramagnetic center with S=1/2 and a rhombic g-tensor. Its paramagnetic behavior is confirmed by the increase of the integrated signal according to a Curie law. The g-tensor principal values are:
g1 = 2.2075 , g2 = 2.1575 , g3 =2.0895
A strong narrowing with temperature is observed. It is discussed in terms of the dipolar interaction with the triplet state dimers randomly distributed around the paramagnetic center. A similar narrowing was observed in Zn doped copper acetate, in which paramagnetic Zn – Cu centers are formed [3]. In this case the narrowing is faster than in our case, so that we assume that the new paramagnetic center is placed in the superficial layer of the powder particles. The g-tensor values support an identification of it as a single Cu2+ ion, but the absence of a resolved hyperfine structure forbids us to give a definitive interpretation.
References.
[1] B. Bleaney, K. D. Bowers, Proc. Roy. Soc., A214 (1952) 451
[2] O. Cozar, V. V. Grecu, V. Znamirovschi, Rezonanta electronica de spin pe complecsi metalici, Edit. Academiei Romane, 2001
[3] A. Kawamori, S. Matsura, H, Abe, J. Phys. Soc. Japan, 12 (1970) 1255
|
|
|
|