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Local Magnetic and Electronic Properties of the A2FeM'O6 (A = Ba, Sr, Ca, M' = Mo, Re) Double Perovskites

100%

Zając D., Sikora M., Prochazka V., Borowiec M., Stępień J., Kapusta C., Riedi P., Marquina C., De Teresa J., Ibarra M.

Acta Physica Polonica A

2007

vol. 111

issue 6

797-820

The results of a combined NMR, X-ray absorption spectroscopy and X-ray magnetic cirrcular dichroism study of the AA'FeMoO_6 and AA'FeReO_6 double perovskites are presented. They revealed a dependence of electronic and magnetic properties, including a d-electron transfer between Fe and Mo sites, on the structural tolerance factor. The maximum value of the 4d Mo electron occupation and the corresponding Mo moment is obtained for the tolerance factor of unity. This corresponds to the maximum strength of the magnetic interaction and, respectively, to the Curie temperature. The dominant T^{5/2} type temperature dependence of the Mo hyperfine field reveals the half-metallicity of the AA'FeMoO_6 compounds. Antisite defects and antiphase boundaries have been identified in NMR measurements and the strength of their magnetic coupling have been determined. A considerable orbital contribution to the Re and Fe magnetic moments were found in the NMR and X-MCD measurements on the AA'FeReO_6 compounds. Its magnitude decreases with increasing structural tolerance factor and is correlated with their magnetic anisotropy.

A ^{55}Mn NMR Study of La_{0.33}Nd_{0.33}Ca_{0.34}Mn O_3 with ^{16}O and ^{18}O

100%

Rybicki D., Kapusta C., Riedi P., Oates C., Sikora M., Zając D., De Teresa J., Marquina C., Ibarra M.

Acta Physica Polonica A

2004

vol. 105

issue 1-2

183-188

A ^{55}Mn NMR study of ^{16}O and ^{18}O containing La_{0.33}Nd_{0.33}Ca_{0.34}Mn O_3 is reported. The spin-echo spectra measured at 4.2 K and zero field consist of a double exchange line corresponding to the ferromagnetic metallic regions. The line intensity is more than an order of magnitude lower for the ^{18}O compound, which indicates an order of magnitude lower content of the ferromagnetic metallic phase in this compound. The frequency dependence of the spin-spin relaxation time T_2 shows a pronounced minimum at the center of the double exchange line of both compounds due to the Suhl-Nakamura interaction, which indicates that the ferromagnetic metallic regions are at least 10~nm in size. The results are discussed in terms of the influence of oxygen isotopic substitution on phase segregation.

NMR Study of (Sr,Ba,La)_2Fe_{1+y}Mo_{1-y}O_6 Double Perovskites

100%

Zając D., Kapusta C., Riedi P., Sikora M., Oates C., Rybicki D., De Teresa J., Serrate D., Marquina C., Ibarra M.

Acta Physica Polonica A

2004

vol. 106

issue 5

759-765

The ^{95}Mo and ^{97}Mo NMR spin-echo study of (Sr,Ba,La)_2Fe_{1 +y}Mo_{1-y}O_6 double perovskites is reported. Powder samples of Ba_{1.44}Sr_{0.36}La_{0.2}FeMoO_6 and (Ba_{0.8}Sr_{0.2})_{2-2x}La_x#_x Fe_{1+y}Mo_{1-y}O_6, where# denotes vacancies, for: x=0, y=0; x=0.1, x=0.2 and x=0.3, y=0 and y=0.2 were measured at 4.2 K and no applied magnetic field. NMR signals are observed at 55-100 MHz for the main line and 30-55 MHz for low-frequency satellite. The main line and the satellite are attributed to the ideal and defect positions of Mo atoms. La and vacancy doping introduce more defects, however, increasing the Fe/Mo ratio decreases the amount of defect Mo sites. La doping causes a satellite pattern at the high frequency side of the spectrum, which is related to different numbers of the La next neighbours. The effect is attributed to an increase in the electron density and the corresponding magnetic moment at the adjacent Mo sites and reveals a local character of the electron doping.

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3 Acta Physica Polonica A

1 2007

2 2004

3 De Teresa J.

3 Ibarra M.

3 Kapusta C.

3 Marquina C.

3 Riedi P.

3 Sikora M.

3 Zając D.

2 Oates C.

2 Rybicki D.

1 Borowiec M.

1 Prochazka V.

1 Serrate D.

1 Stępień J.

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Local Magnetic and Electronic Properties of the A2FeM'O6 (A = Ba, Sr, Ca, M' = Mo, Re) Double Perovskites

A ^{55}Mn NMR Study of La_{0.33}Nd_{0.33}Ca_{0.34}Mn O_3 with ^{16}O and ^{18}O

NMR Study of (Sr,Ba,La)_2Fe_{1+y}Mo_{1-y}O_6 Double Perovskites