Magnetic properties of LaFe1-xCrxO3 and Fe2-2xCr2xO3 mixed oxides

Mixed oxides with formula LaFe1-xCrxO3 and Fe2-2xCr2xO3, where 0≤x≤1, are studied. The samples have been prepared using solid state reaction technique in air. The X-ray diffraction spectra indicated that the samples crystallize in a corundum phase with space group ( R3c ) for Fe2-2xCr2xO3 and in the perovskite structure for LaFe1-xCrxO3. Many techniques have been used to explore the magnetic properties of the systems. High field, ZFC and FC magnetization vs. temperature, d.c. susceptibility and Mössbauer spectroscopy were carried out. High temperature magnetic susceptibility measurements and high field magnetic magnetization (H ≤ 20 T) show that the behavior of the susceptibility and the magnetization are complex. Mössbauer spectra of the solid solutions have been measured at 4.2 K and in the temperature range 77 K to 300 K. The shapes of spectra are unusual, showing strong relaxation phenomena in a wide temperature range as recently observed for many frustrated systems. The results are discussed by establishing the existence of various magnetic structures, inducing intermediate magnetic phases between the antiferromagnetic and the paramagnetic states. Preliminary magnetic phase diagrams of the systems have been established.Mixed oxides with formula LaFe1-xCrxO3 and Fe2-2xCr2xO3, where 0≤x≤1, are studied. The samples have been prepared using solid state reaction technique in air. The X-ray diffraction spectra indicated that the samples crystallize in a corundum phase with space group ( R3c ) for Fe2-2xCr2xO3 and in the perovskite structure for LaFe1-xCrxO3. Many techniques have been used to explore the magnetic properties of the systems. High field, ZFC and FC magnetization vs. temperature, d.c. susceptibility and Mössbauer spectroscopy were carried out. High temperature magnetic susceptibility measurements and high field magnetic magnetization (H ≤ 20 T) show that the behavior of the susceptibility and the magnetization are complex. Mössbauer spectra of the solid solutions have been measured at 4.2 K and in the temperature range 77 K to 300 K. The shapes of spectra are unusual, showing strong relaxation phenomena in a wide temperature range as recently observed for many frustrated systems. The results are discussed by establishing the existence of various magnetic structures, inducing intermediate magnetic phases between the antiferromagnetic and the paramagnetic states. Preliminary magnetic phase diagrams of the systems have been established

Preparation and magnetic interactions in Cd1-x Znx Cr2 Se4 spinel

Cd1-x Znx Cr2 Se4 is a compound with spinel structure where two important frustration effects are present. The disorder in distribution of exchange interactions is due to the substitution between zinc and cadmium on tetrahedral sites. The samples in powder form were performed by the classical ceramic method. For the crystal growth, different methods were used depending on Zn and Cd concentrations. The composition was determined by X-ray measurements of the lattice constant. The direct current susceptibility measurements show that for the whole concentration range the system obey to Curie-Weiss law at high temperature. The DC magnetization, AC susceptibility and thermoremanent magnetization measurements revealed the existence of a spin-glass-like state and reentrant spin-glass behavior at low temperatures, in the middle concentration range.Cd1-x Znx Cr2 Se4 is a compound with spinel structure where two important frustration effects are present. The disorder in distribution of exchange interactions is due to the substitution between zinc and cadmium on tetrahedral sites. The samples in powder form were performed by the classical ceramic method. For the crystal growth, different methods were used depending on Zn and Cd concentrations. The composition was determined by X-ray measurements of the lattice constant. The direct current susceptibility measurements show that for the whole concentration range the system obey to Curie-Weiss law at high temperature. The DC magnetization, AC susceptibility and thermoremanent magnetization measurements revealed the existence of a spin-glass-like state and reentrant spin-glass behavior at low temperatures, in the middle concentration range