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1

Ellipsometric Studies of NdMnO_3 Single Crystals

100%

Babonas G., Reza A., Szymczak R., Baran M., Shiryaev S., Fink-Finowicki J., Szymczak H.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

197-208

EN

Ellipsometric studies of NdMnO_3 single crystals of orthorhombic symmetry were carried out in the spectral range 0.5-5.0 eV. Experimental data, which were obtained on the (001)_{pc}-type planes of pseudo-cubic system, were analyzed in the model of biaxial crystal. For the first time, three componentsε_x,ε_y,ε_z of the effective dielectric function for manganites of orthorhombic symmetry were determined. From ellipsometric data, the spectra of optical conductivity and loss function were also calculated and considered. The fine structure of the spectra and optical anisotropy was the basis for discussion of the microscopic origin of the optical transitions responsible for the optical features. The electronic excitations due to dipole-forbidden spin-allowed transitions of the d-d-type in Mn-ions, f-f-type in Nd-ions and charge-transfer 2p(O)-3d(Mn) transitions were taken into account. The data for NdMnO_3 were compared with those obtained for other related undoped and doped single crystals of perovskite-type structure, LaMnO_3, (LaBa)(MnCo)O_3 and (LaCa)CoO_3.

2

Magnetic Phase Transitions in Pure and Cobalt-Doped Geometrically Frustrated Ni_3V_2O_8 Single Crystals

100%

Szymczak H., Baran M., Szymczak R., Barilo S., Bychkov G., Shiryaev S.

Acta Physica Polonica A

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2007

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vol. 111

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issue 1

71-77

EN

The results of magnetic measurements performed on geometrically frustrated Ni_3V_2O_8 and Ni_{3(1-x)}Co_{3x}V_2O_8 single crystals with x=0.03 are presented. It was found that Co doping did not change considerably the magnetic H-T phase diagram. Although no spin-glass effects were observed, nevertheless, a strong effect of 3 at% cobalt doping was evidenced. The main effect of Co-doping concerns the direction of the antiferromagnetic vector, which for Ni_3V_2O_8 appears along the $a$ axis, while for only slightly Co doped crystals - along the $c$ axis. This switching of direction results from distinct changes of the magnetocrystalline anisotropy due to the presence of Co^{2+} ions strongly coupled to the kagome lattice. The disorder introduced by doping has practically no effect on the magnitude of the isotropic exchange interactions. At the same time the doping suppresses the Dzyaloshinskii-Moriya exchange interactions due to the change of direction of the antiferromagnetic vector.

3

Magnetic Properties of EuBaCo_2O_{5.5} Single Crystals

84%

Baran M., Barilo S., Bychkov G., Gatalskaya V., Kurochkin L., Shiryaev S., Szymczak R., Szymczak H.

Acta Physica Polonica A

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2004

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vol. 105

|

issue 1-2

209-214

EN

The static magnetization of the EuBaCo_2O_{5.5} single crystals was measured from helium to room temperatures for two configurations of the applied field: parallel and perpendicular to the c-axis. The compound is antiferromagnetic from helium temperature to about 210 K. In low temperature region (below 45 K) the antiferromagnetism coexists with a spin-glass-like state. The metamagnetic field-induced phase transition was observed in the antiferromagnetic phase for magnetic field applied perpendicular to the c-axis. The spontaneous phase transition from antiferromagnetic to weak ferromagnetic phase was established to be of the first order. This transition is accompanied by the appearance of the intermediate state. The weak ferromagnetic phase exists up to T_c=240 K.

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3 Acta Physica Polonica A

1 2007

2 2004

3 Baran M.

3 Shiryaev S.

3 Szymczak H.

3 Szymczak R.

2 Barilo S.

2 Bychkov G.

1 Babonas G.

1 Fink-Finowicki J.

1 Gatalskaya V.

1 Kurochkin L.

1 Reza A.

Ellipsometric Studies of NdMnO_3 Single Crystals

Magnetic Phase Transitions in Pure and Cobalt-Doped Geometrically Frustrated Ni_3V_2O_8 Single Crystals

Magnetic Properties of EuBaCo_2O_{5.5} Single Crystals