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1

Giant Magnetoresistance in Melt-Spun Co-Cu Modified by Rare Earths

100%

Idzikowski B., Rössler U., Handstein A., Nenkov K., Müller K.

Acta Physica Polonica A

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2000

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vol. 97

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issue 5

791-794

EN

Samples of the composition RE_{x}Co_{20}Cu_{80-x}, RE = Sm, Gd or Dy (x = 0, 1, and 3) were produced by melt-spinning and subsequent annealing. The magnetoresistance is negative as in granular Co-Cu, but its values depend on the kind of rare earth element added and on changes in the microstructure induced by thermal annealing. An addition of 1 at.% rare earth metal to Co_{20}Cu_{80} yields a considerable increase in the magnetoresistance ratio, whereas an addition of 3 at.% causes a decrease. E.g., by addition of 1 at.% Dy to Co_{20}Cu_{80} and optimal thermal treatment, the value of magnetoresistance ratio measured at 10 K in a field of 5 T increases from -14% to -28%. The effect can be attributed to the presence of clusters of hexagonal Dy(Co,Cu)_{5}, which was ascertained from X-ray diffraction data, or other, metastable rare-earth compounds and paramagnetic rare-earth atoms in the Cu matrix.

2

Probing 3d-4f Exchange Interactions by High-Field Magnetization Measurements

100%

Skourski Y., Kuz'min M., Skokov K., Müller K., Wosnitza J.

Acta Physica Polonica A

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2009

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vol. 115

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issue 1

178-180

EN

In a 4f-3d ferrimagnet the molecular field (a net value expressing the relevant exchange interactions) can be determined from high-field magnetization measurements. If the applied field is high enough, it breaks the ferrimagnetic ground state and drives the system towards ferromagnetic order via non-collinear intermediate phases. Magnetization curves of Er_2Fe_{17} singe crystal were measured along the [100] crystallographic direction in magnetic fields up to 50 T. An unfixed sample, free to rotate, was measured as well. The magnetization measured along the easy magnetization direction shows jumps at 37.5 and 44 T. The first jump was used for the determination of the molecular field (66.4 T). This agrees with the data for the unfixed sample where a kink in the magnetization at 33.5 T yields a molecular field of 65.7 T. The obtained values are in a good agreement with literature data.

3

Electron Transport and Point Contact Spectroscopy of Cubic DyCu_{5}

86%

Nenkov K., Idzikowski B., Ilkovic S., Kačmarčiková E., Reiffers M., Müller K.

Acta Physica Polonica A

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2000

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vol. 97

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issue 5

843-846

EN

The electron transport properties and point contact spectra of melt-spun DyCu_{5} with the cubic phase (structure type AuBe_{5}, space group $F\overline{4}3m$) were investigated. It was found by ac-susceptibility measurements that below a transition temperature T_{m}=6.5 K this phase shows metamagnetism. Between T_{m} and T_{C}=14.5 K a spontaneous magnetization is found. Our measurements of electrical resistivity confirm the existence of two magnetic phase transitions in the compound. Furthermore, we present point contact spectra of DyCu_{5}-Cu heterocontacts which are directly proportional to the electron-quasiparticle interaction function. Apart from a peak at about 18 meV, which is characteristic of electron-phonon interaction in pure Cu, we observed a series of additional maxima at lower energy, which are connected with the allowed 4f-transitions from the ground state to excited crystalline electric field levels.

4

Low-Field Magnetoresistance in Manganite Thin Films

73%

Vlakhov E., Dörr K., Müller K., Handstein A., Nenkov K., Walter T., Chakalov R., Chakalova R., Spasov A.

Acta Physica Polonica A

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2000

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vol. 97

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issue 5

787-790

EN

Grain boundaries play an important role in low-field magnetoresistance of La_{0.7}Ca_{0.3}MnO_{3} and La_{0.7}Sr_{0.3}MnO_{3} thin films deposited by magnetron sputtering and pulsed laser deposition on YSZ(100) and silicon substrates buffered by YSZ. Well-pronounced low-field magnetoresistance hysteresis was observed in magnetic fields applied in in-plane and out-of-plane directions. High values of local magnetoresistance sensitivity d(MR)/dH in the vicinity of the coercive field were obtained reaching up to 0.2%/Oe for La_{0.7}Ca_{0.3}MnO_{3} samples at 5 K.

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4 Acta Physica Polonica A

1 2009

3 2000

4 Müller K.

3 Nenkov K.

2 Handstein A.

2 Idzikowski B.

1 Chakalov R.

1 Chakalova R.

1 Dörr K.

1 Ilkovic S.

1 Kačmarčiková E.

1 Kuz'min M.

1 Reiffers M.

1 Rössler U.

1 Skokov K.

1 Skourski Y.

1 Spasov A.

1 Vlakhov E.

1 Walter T.

1 Wosnitza J.

Giant Magnetoresistance in Melt-Spun Co-Cu Modified by Rare Earths

Probing 3d-4f Exchange Interactions by High-Field Magnetization Measurements

Electron Transport and Point Contact Spectroscopy of Cubic DyCu_{5}

Low-Field Magnetoresistance in Manganite Thin Films