Substitution Of Co For Mn Research Articles

Structure and magnetic properties of Tb2Co17−xMnx compounds

X-ray diffraction (XRD) and magnetization measurements were employed to investigate the effects of Mn substitution for Co on the structure and magnetic properties of Tb2Co17−xMnx compounds with x=0–7. XRD patterns show that all samples are single phase except the samples with x=6 and 7 which contain a small amount of impurity. The substitution of Mn for Co leads to a monotonic increase in unit cell volume. The saturation magnetization at 5 K remains nearly unchanged upon Mn substitution, while the Curie temperature decreases monotonically. XRD measurements on magnetically aligned powders with x=0–7 exhibit an easy-plane type of magnetic anisotropy at room temperature. For x=2, 3, and 4, spin reorientation transitions above room temperature are observed in the M–T curves. The magnetic phase diagram is given.

Structure and magnetic properties of Y2Co17−xMnx (x=0–8) compounds

X-ray diffraction (XRD) and magnetization measurements were employed to investigate the effect of Mn substitution for Co on the structure and magnetic properties of Y2Co17−xMnx compounds with x=0–8. XRD patterns show that all samples are single phase with a hexagonal Th2Ni17-type structure. The substitution of Mn for Co in Y2Co17−xMnx compounds leads to a monotonic increase in unit cell volume. The saturation magnetization remains nearly constant for x⩽3, then decreases quickly with increasing Mn content; this can be explained by the change of the 3d energy band structure and an electron transfer process. The Curie temperature TC is found to decrease rapidly with increasing Mn concentrations. X-ray diffraction measurement on magnetically aligned Y2Co17−xMnx compounds exhibit an easy-plane type of magnetic anisotropy at room temperature for x=0 and an easy-axis type of magnetic anisotropy at room temperature with x=1–7. Substitution of Mn for Co leads to a change of the magnetocrystalline anisotropy of the Co sublattice from the basal plane to the c axis and strongly increases the uniaxial anisotropy of Y2Co17−xMnx. The magnetocrystalline anisotropy field HA is found first to increase and then decrease with increasing Mn concentration, attaining a maximum value of 20.6 kOe at x=3.

The effect of manganese substitution on the magnetic properties of Ce2Co17 compounds

X-ray diffraction (XRD) and magnetization measurements were employed to investigate the effect of Mn substitution for Co on the structure and magnetic properties of Ce2Co17-xMnx compounds with x = 0, 1, 2, 3, 4. XRD patterns show that all samples are single phase with the hexagonal Th2Ni17-type structure. The substitution of Mn for Co in Ce2Co17-xMnx compounds leads to a monotonic increase in unit-cell volume. The saturation magnetization at 5 K and the Curie temperature TC decrease monotonically with increasing Mn content. X-ray diffraction measurements on magnetically aligned Ce2Co17-xMnx powders with x = 0-4 exhibit an easy-axis type of magnetic anisotropy at room temperature. The substitution of Mn for Co leads to a change of the magnetocrystalline anisotropy of the Co sublattice from the basal plane to c-axis and strongly increases the uniaxial anisotropy of Ce2Co17-xMnx compounds. The magnetocrystalline anisotropy field HA is found first to increase and then decrease with increasing Mn concentration, attaining a maximum value of 30.1 kOe at x = 2.

X-ray absorption spectroscopy study of the La 0.7Ba 0.3Mn 1− xCo xO 3 system

We report the transition-metal (Mn and Co) K-edge X-ray absorption spectroscopy (XAS) study of a series of La 0.7Ba 0.3Mn 1− x Co x O 3 ( 0⩽x⩽1) samples. Systematic chemical shifts to higher energy with the Co content ( x) are observed in both Mn and Co K-edge spectra. The chemical shift to higher energy in Mn K-edge spectra is caused by the decreased Mn 3+/Mn 4+ ratio due to Co substitution of Mn. The Co K-edge spectra show that the Co valence is between 2+ and 3+, which also increases with x. The effect of electronic structures on the physical properties are briefly discussed.

Electrical conductivity and magnetic behavior of La 0.67Ca 0.33MnO 3 as influenced by substitution of Co

La 0.67Ca 0.33Mn 1− x Co x O 3 ( x=0.00, 0.05, 0.075, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40) have been investigated by AC susceptibility, DC magnetization and DC electrical resistivity measurements. Substitution of Co for Mn did not cause any change in crystal symmetry, yet electrical conductivity as well as ferromagnetism have been consistently suppressed by the dopant. The results can be explained on the basis of weakening of the double exchange process and an increase in anisotropy of the exchange interaction consequent upon Co doping.

Electronic conductivity in the Pr 1− xSr xCo 1− yMn yO 3−δ system

The effect of Mn substitution for Co and of Sr doping for Pr on the electronic conductivity of Pr 1− x Sr x Co 1− y Mn y O 3−δ ( x=0.3, 0.5, 0≤ y≤1) was investigated. All oxides have an orthorhombic GdFeO 3-type structure (space group Pbnm), as determined by XRD. The pseudo-cubic lattice constant increases with increasing Mn content. The electrical conductivity was measured in the temperature range from 100 to 800°C in air. The substitutionally-mixed compositions exhibit a semiconducting behavior, where the small polaron hopping conductivity model applies. The normalized conductivity shows a sharp decrease when y increases in the range 0< y<0.4, and it reaches a minimum in the range 0.4< y<0.6. The small polaron is trapped at the energetically lower Mn sites, and the slow transition rate to a neighboring Co site dominates the hopping process. At higher y values, the hopping proceeds among adjacent Mn sites, and as a result, an increase of conductivity is observed. The calculated activation energy values agree with the above mechanism.

Heat of formation for LiMyMn2-yO4(M=Co, Cr, Li, Mg, Ni) spinel solid solution

The enthalpy of formation for LiMyMn2−yO4 (M=Co, Cr, Li, Mg, Ni) was measured by a Tian-Calvet type high temperature isothermal microcalorimeter. The standard enthalpy of formation for LiMn2O4 at 876 K was evaluated to be ΔHf0=−1404.2±6.4 kJ mol−1. The partial substitution of Co and Ni for Mn decreased the absolute ΔHf0 value, while that of Cr and Mg for Mn increased the absolute ΔHf0 value. In the case of the partial substitution of Li for Mn, no marked change in ΔHf0 could be observed.

Structure and magnetic properties of GdMn1−xCoxSi compounds

Structural and magnetic properties of the GdMn1−xCoxSi compounds with x=0, 0.2, 0.4, 0.6, 0.8 and 1.0 have been investigated. All the compounds investigated are isotypical and crystallize in the tetragonal PbFCl-type structure. The GdMn1−xCoxSi compounds exhibit ferromagnetic coupling. Substitution of Co for Mn leads to a decrease of the unit-cell volume, of the saturation magnetization at 1.5 K and of the Curie temperature.

Investigation of Magnetic Properties of NdMn2—xCoxGe2 Compounds (x = 0 to 1.0)

The structure and the magnetic properties for the NdMn2-xCoxGe2 compounds (x = 0 to 1.0) have been investigated. All the compounds crystallize in the ThCr2Si2-type structure. Substitution of Co for Mn led to a linear decrease in the lattice constants and the unit cell volume. From the magnetic measurement we have determined two concentration regions of qualitatively different low temperature behavior. Increasing substitution of Co for Mn in NdMn2Ge2 shows a depression of ferromagnetic ordering and a gradual development of antiferromagnetic ordering. For compounds with x < 0.6 ferromagnetic ordering occurs, while for compounds with x greater than or equal to 0.6 antiferromagnetic ordering occurs. The saturation magnetization at 1.5 K for these compounds decreases monotonously with increasing Co content.

Structure and magnetic properties of compounds

compounds with x = 0, 0.05, 0.10, 0.15, 0.20 and 0.25 have been studied in this paper. All of the compounds crystallize in the -type structure (space group P6/mmm). The substitution of Co for Mn in results in a monotonic decrease in the lattice constants and the unit-cell volume. The ordering temperature decreases monotonically from 423 K at x = 0 to 267 K at x = 0.25. The reorientation of the easy-axis magnetization of disappeared on Co substitution at x = 0.10, while for Co content x exceeding 0.15 a compensation temperature was observed in the thermal magnetization curve. The reorientation temperature decreases with Co content increase, while the compensation temperature increases. The magnetization curves up to 70 kOe at 4.5 K are given and the saturation magnetization decreases from at x = 0 to at x = 0.1 and then increases to at x = 0.25.

Magnetic properties of Ni2In type (Co1–xMnx)65Ge35 compounds

The high temperature phase of (Co1–xMnx) 65Ge35 is found to be of the hexagonal Ni2In type in the range of 0≤x≤0.6. Co2Ge is Pauli paramagnetic, and ferromagnetism is induced with substitution of Mn for Co. Magnetization measurement and x-ray diffraction experiments for these compounds have been performed. The x dependences of the Curie temperature Tc and magnetization show a maximum near composition x=0.25. X-ray studies show that the lattice constants c are minimum at x=0.25. The x dependence of the relative intensities of x-ray lines suggests that the Mn and Co atoms at 2(a) sites in the compound x=0.25 align alternately in the c direction. The Co atoms at 2(d) site and the Ge atoms at 2(c) site shift along the c direction are found. The neutron diffraction experiment of x=0.25 also support such crystal structure. Maximum of Curie temperature and magnetization of compounds near x=0.25 are discussed with the ordering of Mn and Co atoms in the crystal lattice.

Effect of Mn-substitution for Co on the crystal structure and acid delithiation of LiMn yCo 1− yO 2 solid solutions

Lithium-manganese-cobalt oxides, LiMn y Co 1− y O 2, where Li/(Mn+Co)≈1and 0< y<1, have been obtained by a solid state reaction between lithium hydroxide and manganese-cobalt spinels in air (0< y<0.2) or under nitrogen (0.2< y<1). The crystal structure of the ternary oxides depends on the Mn/(Mn+Co) ratio: up to y<0.2, oxides with a trigonal structure (s.g. R 3 m) are formed; at 0.2<y<0.7, oxides with a rock-salt type structure (s.g. Fm 3 m) appear; finally, at y<0.7, the oxides obtained have a tetragonal spinel structure (I4 1/amd). Acid delithiation of the lithium-manganese-cobalt oxides proceeds differently depending on their composition and crystal structure. With cobalt-rich oxides, the acid extraction of lithium proceeds within the initial trigonal structure, while with rock-salt and tetragonal oxides acid delithiation yields Li x (Mn y Co 1− y )O 2 oxides with a cubic spinel structure (s.g. Fd3m). Among LiMn y Co 1− y O 2 oxides, lithium is removed more easily and to a higher extent from the tetragonal oxides. Due to the high oxidation degree of the manganese and cobalt ions in delithiated samples, the electrochemical cell consisting of Li/Li x (Mn y Co 1− y )O 2 displays a high discharge voltage (4.1–4.2 V), which allows its direct discharge. The highest reversibility and capacity per formula unit (about 0.75 Li) are observed on manganese-rich spinel oxides with y<0.7.

Features of hydrogen-induced amorphization of the Er(Co, Mn) 2 pseudo-binary Laves compound

Hydrogen-induced amorphization behavior of Er(Co 1− x Mn x ) 2 pseudo-binary Laves compound is investigated by means of X-ray diffractometry and transmission electron microscopy. The substitution of Mn for Co results in a homogenous single phase within the whole composition range. Up to x = 0.8, C15 cubic phase is obtained, but C14 structure is found at higher Mn composition. At all compositions except for the binary ErMn 2, the amorphization phenomena are observed. Thus it is suggested that amorphization of the Laves phases by the hydrogen absorption is not concerned with the crystal structure but the chemical bonding between the unlike atoms causing the kinetic constraints of the motion of the metal atoms. By the Mn addition into ErCo 2, the amorphization temperature, which is defined as the temperature amenable to the full amorphization reaction in a fixed times of 24 h, gradually decreases from 350°C for ErCo 2 to 230°C for Er(Co 0.2Mn 0.8) 2 within the C15 region. This behavior is explained by the variation of the formation enthalpy ( ΔH f) and the bulk modulus of the compound with the Mn content. A compound with a high negative ΔH f and high modulus is amorphized at higher temperature range due to the larger activation energy barrier for the motion of the metal atoms than other compounds with relatively lower heat of mixing and modulus values.

Magnetic phase transitions in the Gd(Mn 1 − xCo x) 2 system

Measurements of magnetization, ac susceptibility, thermal expansion, specific heat and NMR have been carried out on the cubic Laves-phase compounds Gd(Mn 1 - x Co x ) 2. The substitution of Co for Mn makes the antiferromagnetic coupling between Mn moments unstable and results in the ferromagnetic arrangement of 3d moments above x = 0.35. The results are discussed on the basis of the itinerant 3d-electron model. On the other hand, the Gd moments in the ground state are in a freezing state with a random configuration for 0 ≤ x ≤ 0.025, in a canted state for 0.05 ≤ x < 0.3 and in a ferromagnetic state for x ≥ 0.35. The freezing state of Gd moments for x ≤ 0.025 may be realized by slight but intrinsic randomness in the arrangement of atoms in addition to the competing state of the exchange interactions.