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1

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

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2004

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vol. 105

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issue 1-2

183-188

EN

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.

2

An NMR study of Pr_{0.5}Ca_{0.5}Mn_{1-x}Ga_xO_3 (x=0 and 0.03)

100%

Oates C., Kapusta C., Riedi P., Sikora M., Zając D., Rybicki D., Martin C., Yaicle C., Maignan A.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

189-195

EN

An NMR study of polycrystalline Pr_{0.5}Ca_{0.5}Mn_{1-x}Ga_xO_3 (x=0 and 0.03) at 3 K is presented. Zero field spin-echo spectra of the Ga doped compound consist of an overlapping ^{69,71}Ga signal at 74~MHz (hyperfine field of 5.3 T), a ^{55}Mn double exchange line at 375 MHz (35.5 T) and a weak Mn^{3+} signal between 400 and 550 MHz. Measurements in an applied field show a step-like increase in the double exchange line intensity, which corresponds to an increase in the amount of the ferromagnetic metallic phase. This coincides with a step-like feature in the bulk magnetization measurements. The effect is similar to that in the previous field dependent ^{55}Mn NMR measurements of Pr_{0.67}Ca _{0.33}MnO_3. At the demagnetized and remanent state, a variation of spin- spin relaxation time, T_2, across the ^{55}Mn line, due to the Suhl-Nakamura interaction is observed, which suggests that the ferromagnetic metallic double exchange regions, at liquid helium temperatures, are at least 4 nm in size.

3

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

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2004

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vol. 106

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issue 5

759-765

EN

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

3 2004

3 Kapusta C.

3 Oates C.

3 Riedi P.

3 Rybicki D.

3 Sikora M.

3 Zając D.

2 De Teresa J.

2 Ibarra M.

2 Marquina C.

1 Maignan A.

1 Martin C.

1 Serrate D.

1 Yaicle C.

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

An NMR study of Pr_{0.5}Ca_{0.5}Mn_{1-x}Ga_xO_3 (x=0 and 0.03)

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