Cu For Mn Research Articles

Magnetic Phase Diagram of the Intermetallic LaMn2‐xCuxSi2 Silicides.

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Magnetic ordering of the Pr sublattice with the substitution of Cu for Mn inPrMn2Si2 intermetallics

The magnetic properties of PrMn2−xCuxSi2 () were studied by field-cooled and zero-field-cooled magnetization measurements in thetemperature range 5 K K in low external fields (5 mT) and by magnetic-field-dependent magnetization measurementsin fields up to 5.5 T. Substitution of Cu for Mn leads to a linear decrease in the lattice constantc and the unitcell volume V and a linear increase in the lattice constanta. Earlier neutron diffraction experiments showed that Pr does not order down to 1.6 K inPrMn2Si2 while the ferromagnetic Mn planes are ordered antiparallel along thec axis. With the increasing Cu content, the magnetization increases rapidly at lowtemperatures for the samples with . Cu substitution strongly changes the magnetic properties and leads to the magneticordering of the Pr sublattice. This is mainly deduced from the discussion of the valuesof the magnetic moments at low temperatures. Below the Curie temperaturesTC, the spins in the Mn sublattice are arranged parallel to the Pr sublattice. With increasing Cu,TC(x) has a maximumvalue of 155 K at x = 0.6 and decreases for samples with .

Sol–gel synthesis and magnetization study of Mn 1− xCu xFe 2O 4 ( x=0, 0.2) nanocrystallites

The magnetic nanoparticles of Mn 1− x Cu x Fe 2O 4 ( x=0, 0.2) were prepared by using a sol–gel method. It is proved that both the MnFe 2O 4 and Mn 0.8Cu 0.2Fe 2O 4 nanoparticle samples have superparamagnetic feature. Although the particle sizes are the same, substitution of a small fraction Cu for Mn results in the increase of magnetocrystallite anisotropy energy, thus enhances the blocking temperature from 130 K for MnFe 2O 4 to 260 K for Mn 0.8Cu 0.2Fe 2O 4. Mössbauer spectroscopy confirms that the anisotropy constant K of the Mn 0.8Cu 0.2Fe 2O 4 material is distinctly higher than that of the MnFe 2O 4 compound. Increase of the blocking temperature suggests that the approach we employed is effective to tackle the ‘superparamagnetic limit’ problem.

Magnetic phase diagram of the intermetallic LaMn2−xCuxSi2 silicides

X-ray diffraction (XRD), differential scanning calorimetry (DSC) techniques and AC magnetic susceptibility measurements have been carried out on polycrystalline LaMn2−xCuxSi2 (0.0≤x≤1.0) silicides to investigate how the ferromagnetic and antiferromagnetic regions in LaMn2Si2 are affected by Cu substitution. All compounds crystallize in the ThCr2Si2-type structure with the space group I4/mmm. Substitution of Cu for Mn leads to a linear decrease in the lattice constant c and the unit-cell volume V and a linear increase in the lattice constant a. In all the samples, ferromagnetic interactions within the Mn sublattice take place below the Curie temperature TC(Mn). The onset of ferromagnetism at TC(Mn) decreases with the copper content from 308 (x=0) to 82K (x=1). The temperature dependence of the AC susceptibility shows a distinct feature for x≤0.6 at temperatures below TC(Mn). These samples have a mixed state composed of ferromagnetic and antiferromagnetic phases. The samples with x≤0.2 have a Néel temperature associated with antiferromagnetic behavior above room temperature. A magnetic phase diagram as a function of Cu concentration in LaMn2−xCuxSi2 has been constructed.

Magnetic Properties of NdMn2‐xCuxGe2 Compounds.

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Magnetic properties of NdMn 2− xCu xGe 2 compounds

The structure and magnetic properties of NdMn 2− x Cu x Ge 2 (0.0≤ x≤1.0) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr 2Si 2-type structure with space group I4/ mmm. Substitution of Cu for Mn leads to a linear decrease in the lattice constant c and the unit cell volume V and a linear increase in the lattice constant a. Increasing substitution of Cu for Mn shows a depression of ferromagnetic ordering. The observed phase transitions are summarized in a magnetic x− T phase diagram and compared with previous neutron diffraction results for x=0.0.

Oxygen Stoichiometry in LaMn1‐xCuxO3+y by Thermogravimetry

Thermogravimetry in reducing atmospheres was used to study the oxygen Stoichiometry of several Cu‐substituted lanthanum manganates. The oxygen content of the samples at various levels of reduction (to La2O3, MnO, and Cu) was calculated from the gravimetric data. Freeze‐dried samples prepared by firing at 1100°C in O2 and cooling in O2 had the following composition: LaMnO3.13, LaMn0.7Cuo.3O2.96, LaMn0.5Cu0.5O2.93, and LaMn0.3Cu0.762.71. Single‐phase perovskite structure was obtained in all but the last. The lanthanum manganate LaMnO3.13 was reduced to LaMnO3.00, which shows considerable stability. A 50% substitution of Cu for Mn gave LaMn0.5 Cu0.5O2.93, indicating that the ions involved were mostly Mn4+ and Cu2+. This compound could be reduced to LaMng0.5Cu0.5 O2.26 (largely Mn2+ and Cu1+) without destroying the perovskite structure. This reduced phase could be reoxidized to the original oxygen level but subsequent reduction required considerably higher temperatures and was accompanied by the precipitation of Cu‐rich phases. Samples with a Cu:Mn ratio 30:70 and 70:30 were O‐deficient. The compound LaMn0.7 Cuo.3O2.96 reduced to LaMn0.7Cu0.3O2.54, a relatively stable composition. The highly Cu‐rich sample LaMn0.3Cu0.7O2.71 was easily reduced.