Impurities in Magnetic Materials Studied by PAC Spectroscopy

2011 ◽  
Vol 311 ◽  
pp. 39-61 ◽  
Author(s):  
Artur Wilson Carbonari ◽  
José Mestnik-Filho ◽  
Rajendra Narain Saxena
Keyword(s):  
Rare Earth ◽  
Transition Metal ◽  
Magnetic Fields ◽  
Rare Earth Elements ◽  
Magnetic Hyperfine Field ◽  
Heusler Alloys ◽  
Local Fields ◽  
Pac Spectroscopy ◽  
Open Issue ◽  
Local Magnetic Fields

Perturbed gamma-gamma angular correlation (PAC) spectroscopy is a precise and highly efficient tool to follow the temperature dependence of local magnetic fields in any material. Its resolution and efficiency does not depend on temperature and therefore can measure local fields at low as well as high temperature with the same accuracy. Due its versatility in using different probe nuclei it can sense the local magnetic fields at different sites in the crystalline structure of materials. In this review, important results obtained with PAC spectroscopy are shown in two classes of materials: transition metal and transition-metal based compounds and rare earth elements and rare-earth-element based compounds using mainly three different probe nuclei:111Cd,181Ta and140Ce. PAC spectroscopy has contributed to the systematic study of the magnetic hyperfine field in impurities in matrices of Fe, Co and Ni as well as in transition-metal based Heusler alloys. It has also provided important contribution to the investigation of magnetism in rare-earth elements and intermetallic compounds. An still open issue concerning the local fields in metallic magnetic compounds and elements is the exchange interaction between the magnetic ions of the host and a dilute magnetic impurity, which acts as a defect in the magnetic lattice. PAC spectroscopy has been contributing to study this problem with success. Also shown in this review is the crucial role of ab-initio first principle calculations in the interpretation of PAC results.

scholarly journals Facile Chemical Synthesis of Doped ZnO Nanocrystals Exploiting Oleic Acid

Nanomaterials ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 1150 ◽  
Author(s):  
Sugata Barui ◽  
Roberto Gerbaldo ◽  
Nadia Garino ◽  
Rosaria Brescia ◽  
Francesco Laviano ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Rare Earth ◽  
Oleic Acid ◽  
Magnetic Resonance ◽  
Transition Metal ◽  
Rare Earth Elements ◽  
Resonance Imaging ◽  
Metal Elements ◽  
Doped Zno ◽  
Transition Metal Elements

Zinc oxide nanocrystals (ZnO-NCs) doped with transition metal elements or rare earth elements can be probed for magnetic resonance imaging to be used as a molecular imaging technique for accurate diagnosis of various diseases. Herein, we use Mn as a candidate of transition metal elements and Gd as a presenter of rare earth elements. We report an easy and fast coprecipitation method exploiting oleic acid to synthesize spherical-shaped, small-sized doped ZnO-NCs. We show the improved colloidal stability of oleate-stabilized doped ZnO-NCs compared to the doped ZnO-NCs synthesized by conventional sol–gel synthesis method, i.e., without a stabilizing agent, especially for the Mn dopant. We also analyze their structural, morphological, optical, and magnetic properties. We are able to characterize the persistence of the crystalline properties (wurtzite structure) of ZnO in the doped structure and exclude the formation of undesired oxides by doping elements. Importantly, we determine the room-temperature ferromagnetism of the doped ZnO-NCs. This oleate-stabilized coprecipitation method can be subjected as a standard procedure to synthesize doped and also co-doped ZnO-NCs with any transition metal elements or rare earth elements. In the future, oleate-stabilized Gd/Mn-doped ZnO-NCs can be exploited as magnetic resonance imaging (MRI) contrast agents and possibly increase the signal intensity on T1-weighted images or reduce the signal intensity on T2-weighted images.

scholarly journals Measurements of local magnetic fields in a solar flare by splitting of emissive peaks in cores of spectral lines

2018 ◽  
pp. 47-52 ◽  
Author(s):  
V. Lozitsky
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Flare ◽  
Filling Factor ◽  
Spectral Lines ◽  
Local Fields ◽  
Strong Component ◽  
Component Structure ◽  
Local Magnetic Fields ◽  
The Magnetic Field

We present study of solar flare of 19 July 2000 which arose in active region NOAA 9087 and had M 5.6 / 3N importance. Observational material was obtained with the Echelle spectrograph of the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National University of Kyiv. The local magnetic fields in this flare were measured by the splitting of emissive peaks of the FeI 5269.54, FeII 4923.93, Нα, Нβ, Нγand D3 HeI lines. The basic idea of the method is based on the fact that the flare emission in some spectral lines is clearly divided into two components: (1) wider and unpolarized, and (2) more narrow and polarized, with significant Zeeman splitting. This is indication to the two-component structure of the magnetic field, with substantially different magnetic fields and thermodynamical conditions in these two components. Due to the fact that the polarized emission is quite confidently separated from the unpolarized, it is possible to measure the local magnetic fields directly in the second (strong) component regardless of the filling factor. It was found that in the bright place of this flare, which was projected on the sunspot penumbra, the effective magnetic field Beff in the FeI 6301.5 i 6302.5 lines measured by splitting of the Fraunhofer profiles, was 900 G. However, the splitting of emissive peaks in Нα, Нβ, Нγ and D3 lines corresponds to 1000 G, 1400 G, 1450 G and about zero, respectively, with errors of 30-50 G for abovenamed FeI lines and about 100–150 G for other lines. This difference in the results is probably due to the fact that in the case of FeI 6301.5 i 6302.5 lines, the Beff value represents several parameters, including the value of the background field, the filling factor, and the intensity of the local fields in the strong component. In contrast, data on the Нα, Нβ, Нγ, and D3 lines mainly reflect local fields in the strong component and indicate the nonmonotonous distribution of the magnetic field with height in solar atmosphere, with its maximum at the chromospheric level. Earlier in this flare, when constructing its semi-empirical model, local amplification of the magnetic field at the photospheric level was discovered, and its value reached 1500 G. These data are confirmed by direct measurements of splitting of emissive peaks in FeI 5269.54 and FeII 4923.93 lines, according to which the magnetic field in the flare was 1250 ± 100 G. Thus, in this flare there were at least two regions (possibly two flat layers) of local amplification of the magnetic field.

Tri-axial magnetic alignment and rare-earth-dependent tri-axial magnetic anisotropies in REBa2Cu4O8 cuprate superconductors

2013 ◽  
Vol 1654 ◽  
Author(s):  
M. Yamaki ◽  
M. Furuta ◽  
T. Doi ◽  
J. Shimoyama ◽  
S. Horii
Keyword(s):  
Magnetic Field ◽  
Rare Earth ◽  
Magnetic Fields ◽  
Rare Earth Elements ◽  
Single Crystals ◽  
Cuprate Superconductors ◽  
Ambient Pressure ◽  
Axial Orientation ◽  
Magnetic Alignment ◽  
Flux Method

ABSTRACTWe report the growth of single crystals by a flux method in ambient pressure and tri-axial orientation under modulated rotation magnetic fields (MRFs) on REBa2Cu4O8 (RE124, RE; rare earth elements) compounds. RE124 crystals were grown for RE = Y, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb through appropriate choice of source compounds. All the obtained RE124 powders were tri-axially aligned in MRF of 10T, whereas magnetization axes depended on the type of RE. Moreover, it was found from the changes in the degrees of c-axis and inplane orientation that tri-axial magnetic anisotropies of RE124 also depended on the type of RE. This indicates that it appropriate choice of RE is important for the fabrication of tri-axial oriented ceramics in lower magnetic field conditions.

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