Hidetaro Abe

Paramagnetic Resonance Spectra of Some Cupric Salts (I)

The paramagnetic resonance spectra of some ammine, ethylenediammine, and pyridine derivatives of hydrated cupric salts were examined, using their single crystals and microwaves of λ=32∼5 mm. In the cases of [Cu(NH 3 ) 4 ] SO 4 ·H 2 O and [Cu(en) 2 ] Cl 2 · x H 2 O, detailed analysis of spectra was performed using the structural data from x-ray analysis given by Mazzi. In the other cases, analysis was discussed under an assumption of inequivalent magnetic units. Results thus obtained are fully explained by the treatments given by Abragam and Pryce with modified λ, the spin-orbit coupling coefficient, so the forces acting between the central copper ion and the surrounding nitrogen atmos are supposed to be mainly ionic rather than covalent, as in the cases of usual hydrates. Exchange energies between copper ions are also discussed.

Proton Nuclear Magnetic Resonance Study in Manganese Formate Dihydrate

Proton NMR in single crystals of Mn(HCOO) 2 ·2H 2 O has been observed at the temperature region from 2.5°K to 300°K. The shift of the resonance lines is explained by a dipole sum carried out by the use of atomic parameters presumed from those of the isomorphous magnesium formate. The results give a good agreement with the experimental data obtained above 4.2°K, if the magnetic moments of two kinds of manganese ions in the crystal are assumed to be \(c_{i}H/(T+\varTheta)\) for those of the one kind and to be c i H / T for the other, where c i is g 2 β 2 S ( S +1)/3 k , g =2.00, S =5/2, and \(\varTheta\) is 9.4±0.7°K. Since an abrupt shift of the NMR lines occurs at 3.70±0.05°K, a magnetic transition is thought to exist at this temperature. It is presumably due to a sort of magnetic ordering in the one set of ions which is found to have an antiferromagnetic temperature dependence. At this temperature, a change in ESR spectrum and a sharp peak in the susceptibility are also found. Below this temperature, one...

Paramagnetic Resonance Absorption in K2CuCl4·2H2O

Single crystals of K 2 CuCl 4 ·2H 2 O and (NH 4 ) 2 CuCl 4 ·2H 2 O were examined at 7 different frequencies of microwaves (from 5.4 mm to 6.2 cm wave-lengths). If there were no exchange coupling, two absorption peaks would be expected corresponding to different g -values of two dissimilar Cu ++ ions in unit cell. Experimentally, however, only one peak can be observed at, longer wave-lengths, though the line width remarkably increases with decreasing wavelengths. At the wave-length of 5.4 mm two isolated peaks can be observed. These facts can be interpreted in terms of exchange interaction between dissimilar ions. The exchange energy estimated from these data is greater than 0.1 cm -1 . On the other hand, the width for the c -axis, where the situations of two Cu ++ groups are identical, decreases with decreasing wave-lengths to aboutthe value 1/4 of that at long enough wave-length. According to the treatment by Anderson and Weiss, this result may be explained by their “10/3” effect.

Paramagnetic Resonance in Copper Acetate Monohydrate

At four microwave frequency bands (λ=78, 10, 16 and 32 mm), single crystals of copper acetate monohydrate, Cu(CH 3 COO) 2 H 2 O, were examined at room temperature by the method of paramagnetic resonance absorption, the results differing somewhat from those of usual copper salts. They can be explained by a spin-Hamiltonian with an effective spin S =1 which is considered to be originated from a pair of Cu ++ ions each in 2 D state, holding a strong interaction between them. This is consistent with the results of X-ray crystallography; this crystal consists of bimolecular units Cu 2 (CH 3 COO) 4 ·2H 2 O, in which two copper ions approach as close as 2.64 A. Exchange energy between these copper ions in the unit was estimated using the parameters determined from the resonance spectra and its temperature dependence is discussed.

On Line Widths of Paramagnetic Resonance Absorption

Paramagnetic resonance absorption of microwave (9970 MC) by thirteen salts containing manganese or copper ions was observed with special attention to obtain correct line shapes. The widths obtained were plotted against 1/ a 3 , a being the lattice constant when the arrangement of ions are considered as simple cubic lattice. For smaller values of 1/ a 3 , line shapes are near to gaussian type and the widths coincide with those by dipolar coupling calculated by Van Vleck. When 1/ a 3 is larger, that is, when ions come nearer, line shapes are near to resonance types and widths are in general smaller than those expected by dipolar coupling. This narrowing is caused by the existence of exchange coupling between magnetic ions. It is shown that the narrowing in salts of Mn ++ , Fe +++ (S-state) and C ++ can be related to the value of θ in the Curie-Weiss law of static susceptibility \(\chi_{s}{\backsim}C/(T+\theta)\).

Magnetic Properties of Manganese Formate Dihydrate below 1°K

The magnetic susceptibility of powder and single crystal manganese formate has been measured in the temperature region between 0.1°K and 1.5°K. Powder susceptibility between 1.5° and 0.7°K gives a Curie-Weiss law, 0.6 C /( T +0.2), where C is N g 2 β 2 S ( S +1)/3 k . Single crystal susceptibilities show a small anisotropy at this temperature region. These facts can be regarded as an evidence for the remaining of paramagnetic spins after the previously reported two transitions at 3.7°K and at 1.7°K. At about 0.6°K another transition has been observed in addition to the above mentioned ones. This newly observed transition indicates the ordering of the residual free spins.

Paramagnetic Resonance Absorption in Copper Formate

Paramagnetic resonance in single crystals of copper formate tetrahydrate and its dehydrate was investigated at room temperature with microwaves of λ=11∼5 mm. Either crystal has only one absorption peak at any direction of static magnetic field. The line width of the tetrahydrate is 400 oer. in order and that of dehydrate is 200 oer. The shape of these lines is Lorentzian.

Paramagnetic Resonance in Copper Propionate Monohydrate

Paramagnetic resonance absorption was investigated at centimeter wavelength region in single crystals of copper propionate monohydrate Cu(CH 3 CH 2 COO) 2 ·H 2 O. The spectrum obtained is not a normal one expected for a 2 D state of Cu ++ ions in crystals but similar to that observed in copper acetate monohydrate Cu(CH 3 COO) 2 ·H 2 O and more complicated. This spectrum can be explained by an effective spin Hamiltonian with an equivalent spin value S =1. This may lead us to a conclusion that each of the magnetic complexes in this crystal consists of a pair of copper ions under a strong interaction and may be created from a bimolecular structure, Cu 2 (CH 3 CH 2 COO) 4 ·2H 2 O as in the case of the acetate. The unit cell of this crystal contains six spatially inequivalent pairs, of which three can be derived from the others by a reflection in its ac-plane. Each pair of ions in this crystal is considered to be under a very similar environment, except the direction of the pairs. The rhombicity in its crystal...

Temperature Dependence of an NH4Cl:Cu++ System Studied by ESR

Centre I of Cu 2+ in NH 4 Cl single crystals has been studied at 9 and 35 GHz in a temperature range from 4.2 to 420 K. The centre gives a rhombic spectrum at 4.2 K explainable by a |3 z 2 - r 2 > function with 20% admixture of | x 2 - y 2 > and a tetragonal one above 60 K, both of which disappear at 160 K. Another tetragonal spectrum appears above 330 K, though the lines corresponding to H // z can be observed independent of temperature. The model presented for the centre is a Cu 2+ ion placed at the face-centre of four Cl - ions which make a rhomb at 4.2 K and associated with a vacancy at one of two adjoining NH 4 + sites. The motion of ligands, four Cl - ions and one NH 4 + , is used to explain the temperature dependent spectra, including a disappearance of Cl shfs around 16 K, and their abrupt change at the lambda temperature of NH 4 Cl.

ESR Measurements at Temperatures around 0.1 K

An ESR system is described which operates at 9 GHz in the temperature range from 4.2 K down to 37 mK realized by the method of adiabatic demagnetization, while a specimen is exposed to a magnetic field of 3000 gauss. The process to give the resonance absorption, together with some results obtained as a check of the process, is also reported.