Ioan Burda

X-ray K edge absorption and magnetic behaviour of chromium in stoichiometric and nonstoichiometric α-Cr2O3

Abstract The chemical shift in stoichiometric and nonstoichiometric α-Cr 2 O 3 was determined from the X-ray absorption Cr K edge spectra. The difference in the chemical shifts is produced by the decrease in the valence charge of chromium in the nonstoichiometric compound. Measurements of the temperature dependence of the reciprocal susceptibility between 100 and 1200 K show an antiferromagnetic behaviour for both compounds, with the Neel temperature at 318 K. A big difference in the paramagnetic region was revealed for the compounds investigated. For both compounds, between 318 and 530 K the magnetic susceptibility obeys the Curie-Weiss law, with an effective magnetic moment per chromium ion of 4.86 μ B , very close to the calculated value of 4.9 μ B /Cr 2+ ). For the stoichiometric compound, over 530 K, the slope of the Curie-Weiss line increases and the effective magnetic moment is 3.83 μ B , very close to the calculated value of 3.8 μ B /Cr 3+ .

STRUCTURAL AND MAGNETIC BEHAVIOR OF HIGH TcY1−xGaxBa2Cu3O7−δ SUPERCONDUCTORS

Four samples of high Tc superconductors Y1−xGaxBa2Cu3O7−δ, with x=0.2; 0.3 and x=1 were synthesized. The resulted samples were analysed from a structural and magnetic view point. The X ray spectrum relieved the existence of the orthorhomhic structure and some of unreacted BaCO3 and CuO lines. The temperature dependence of the magnetic susceptibility pointed out the diamagnetic transmission with the critical temperature at 79 K for x=0.2 and 0.3. For the samples x=1 sintered at 1,223 and at 1,273 K the critical temperatures were 77, 5 and 78 K.

Structural and magnetic characteristic of the intermetallic compounds Ho2Al17 and Ho2Ni17

Abstract It is for the first time that the intermetallic compound Ho2Al17 was prepared. The compound is paramagnetic and obeys the Curie-Weiss law with Θp = 18 K and μeff/fu = 14.89 μB and crystallizes in the hexagonal structure with the lattice parameters a = 9.80 A and c = 8.76 A . The intermetallic compound Ho2Ni17 crystallizes in the hexagonal structure with a = 8.32 A and c = 8.03 A . The compound is ferrimagnetic with TC = 612 K and the effective magnetic moment per formula unit determined from the paramagnetic region is μeff/fu = 16.51 μB, very close to the theoretical value 16.44 μB. The Curie temperature for the once melted samples is 462 K and shifts up to 612 K for the samples heated in the magnetic field (0.95 T) at 1150 K during 1 h.

Structural and magnetic properties of the intermetallic compounds Er2Ni17 and Er2Al17

The intermetallic compound Er2Ni17 has a hexagonal lattice of the Th2Ni17 type, with the lattice parameters a = 8.287 A and c = 8.039 A. We have also prepared the compound Er2Al17 which is isotypic with Er2Ni17 and has the lattice parameters a = 9.720 A and c = 8.707 A. The magnetic characteristics of these intermetallic compounds have been investigated in the paramagnetic region. The compound Er2Ni17 is ferrimagnetic, while Er2Al17 is paramagnetic with a Curie temperature Θp = 6 K.

Itinerant ferromagnetism in Mn4N

Abstract This paper reports the temperature dependence of the specific intensity of magnetization and of the magnetic susceptibility of Mn4N between 100 and 1300 K. Mn4N is ferromagnetic below 784 K and in the paramagnetic region presents a Pauli quadratic temperature dependence of the magnetic susceptibility. This means that Mn4N is an itinerant ferromagnet. The existence of the Mn4N compound was confirmed by X-ray analysis.

Calculation of the crystal field and paramagnetic susceptibility of single-crystal rare-earth intermetallic compounds RCu2

Abstract The crystal-field parameters Vmnof PrCu2, NdCu2, TbCu2, DyCu2, HoCu2 and ErCu2 were calculated from the point-charge model and a least-squares fit to the reciprocal susceptibilities along the principal axes. The results of calculation are in good agreement with the experimental values estimated from the anisotropic paramagnetic Curie temperatures on the basis of the molecular field approximation. The influence of the orthorhombic crystal field of RCu2 compounds on their paramagnetic susceptibility along the principal axes was calculated. At the higher temperature range, the anisotropic Curie-Weiss law is valid. At moderate temperatures, for all intermetallic compounds, a deviation of the reciprocal paramagnetic susceptibility from the Curie-Weiss law was found. Its magnitude is in good agreement with experiment.

Magnetic behavior of the pseudobinary intermetallic compounds Er2Ni17−xAlx

Abstract The intermetallic compounds Er 2 Ni 17 and Er 2 Al 17 are isostructural and exhibit limited solid solutions with general formula Er 2 Ni 17− x Al x (0 ⩽ x ⩽ 10), having a hexagonal structure of the Th 2 Ni 17 type. The pseudobinary intermetallic system was investigated in the magnetically ordered and paramagnetic states. The system is ferrimagnetic and the thermal variation of the specific intensity of magnetization drops in two stages. A high critical Curie temperature, T C , is characteristic for this system. The temperature dependence of the reciprocal magnetic susceptibility obeys the Neel law.

Magnetic High Tc Superconducting like Behavior of β-, β″- and γ-Alumina

β, β″ and γ-Al2O3 samples were synthesized. The temperature dependence of the magnetic susceptibility has anomalous diamagnetic-paramagnetic transitions, like Meissner effect, around 80 K, and consequently high Tc superconducting like magnetic behavior.

Magnetic Behavior and Chemical Shift of Amorphous Cr2O3

The chemical shift in cristalline and amorphous Cr2O3 was determined from the X-ray absorption Cr K edge spectra. The measurements of the temperature dependence of the reciprocal susceptibility between 100 and 1200 K show an antiferromagnetic behavior for the cristalline sample, with the Neel temperature at 318 K, and a linear dependence (Curie-Weiss law) with θp<0, for the amorphous oxide.

Magnetic and Structural Characteristics of Amorphous and Crystalline α-Al2O3 High TC Superconductors

The amorphous and crystalline α-Al2O3 oxides were investigated from magnetic and structural point of view. The temperature dependence of the magnetic susceptibility experiences double diamagnetic transition. First diamagnetic-paramagnetic transition is connected with the superconductor-paramagnetic transition, and the second is connected with the diamagnetic-normal state transition of α-Al2O3-amorphous and crystalline phase. The crystalline α-Al2O3 phase has the critical temperature Tc(χ = 0) = 78 K and amorphous phase has the critical temperature much higher temperature Tc(χ = 0)= 144 K.