Influence of oxygen vacancies on the magnetic and electrical properties of La <InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\mathsf{_{1-x}}$</EquationSource> </InlineEquation>Sr<InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\mathsf{_{x}}$</EquationSource> </InlineEquation>MnO <InlineEquation ID="Equ3"> <EquationSource Format="TEX">$\mathsf{_{3-x/2}}$</EquationSource> ...
The crystal structure, magnetization and electrical transport depending on the temperature and magnetic field for the doped stoichiometric <InlineEquation ID="Equ4"> <EquationSource Format="TEX">${\rm La}_{1-x}^{3 + } {\rm Sr}_x^{2 + } {\rm Mn}_{1-x}^{3 + } {\rm Mn}_x^{4 + } {\rm O}_3^{2-} $</EquationSource> </InlineEquation> as well as anion-deficient <InlineEquation ID="Equ5"> <EquationSource Format="TEX">${\rm La}_{1-x}^{3 + } {\rm Sr}_x^{2 + } {\rm Mn}^{3 + }{\rm O}_{3-x/2}^{2-} $</EquationSource> </InlineEquation> (<InlineEquation ID="Equ6"> <EquationSource Format="TEX">$0\le x \le 0.30$</EquationSource> </InlineEquation>) ortomanganite systems have been experimentally studied. It is established that the stochiometric samples in the region of the <InlineEquation ID="Equ7"> <EquationSource Format="TEX">$0 \le x \le 0.125$</EquationSource> </InlineEquation> are an <InlineEquation ID="Equ8"> <EquationSource Format="TEX">${\rm O}'$</EquationSource> </InlineEquation>-orthorhombic perovskites whereas in the <InlineEquation ID="Equ9"> <EquationSource Format="TEX">$0.175 \le x \le 0.30$</EquationSource> </InlineEquation> - a rhombohedric. For the anion-deficient system the symmetry type of the unit cell is similar to the stoichiometric one. As a doping level increases the samples in the ground state undergo a number of the magnetic transitions. It is assumed that the samples with the large amount of oxygen vacancies are a cluster spin glasses (<InlineEquation ID="Equ10"> <EquationSource Format="TEX">$0.175 > x \le 0.30$</EquationSource> </InlineEquation>) and temperature of the magnetic moment freezing is ~40 K. All the anion-deficient samples are semiconductors and show considerable magnetoresistance over a wide temperature range with a peak for the x=0.175 only. Concentration dependences of the spontaneous magnetization and magnetic ordering temperature for the anion-deficient <InlineEquation ID="Equ11"> <EquationSource Format="TEX">${\rm La}_{1-x}^{3 + } {\rm Sr}_x^{2 + } {\rm Mn}^{3 + }{\rm O}_{3-x/2}^{2-} $</EquationSource> </InlineEquation> system have been established by the magnetic measurements and compared with those for the stoichiometric <InlineEquation ID="Equ12"> <EquationSource Format="TEX">${\rm La}_{1-x}^{3 + } {\rm Sr}_x^{2 + } {\rm Mn}_{1-x}^{3 + } {\rm Mn}_x^{4 + } {\rm O}_3^{2-} $</EquationSource> </InlineEquation> one. The magnetic propeprties of the anion-deficient samples may be interpreted on the base of the superexchange interaction and phase separation (chemical disorder) models. Copyright Springer-Verlag Berlin/Heidelberg 2004
