Abstract:~ 7K. The Fe doping quickly depresses Tc, completely destroying the superconducting state for x
0.04. The establishment of an ordered magnetic state is only observed for Fe concentration (x > or = 0.3) far above the concentration for which the superconducting state has completely disappeared. An expansion of the lattice with the increase of the Fe content was observed.]]>
“…[13][14][15][16][17][18][19][20][21][22] In none of the above cases, a definite magnetic solution was found feasible. For Co substitutions the experimental results are unambiguous over the fact that T C decreases as Co at.…”
First-principles, density-functional based electronic structure calculations are carried out for MgC͑Ni 1−x Co x ͒ 3 alloys over the concentration range 0 ഛ x ഛ 1, using Korringa-Kohn-Rostoker coherentpotential approximation method in the atomic sphere approximation. The self-consistent calculations are used to study the changes as a function of x in the equation of state parameters, total and partial densities of states, magnetic moment and the on-site exchange interaction parameter. To study the magnetic properties as well as its volume dependence, fixed-spin moment calculations in conjunction with the phenomenological Landau theory are employed. The salient features that emerge from these calculations are ͑i͒ a concentration independent variation in the lattice parameter and bulk modulus at x ϳ 0.75 with an anomaly in the variation of the pressure derivative of bulk modulus, ͑ii͒ the fixed-spin moment based corrections to the overestimated magnetic ground state for 0.0ഛ x ഛ 0.3 alloys, making the results consistent with the experiments, and ͑iii͒ the possibility of multiple magnetic states at x ϳ 0.75, which, however, requires further improvements in the calculations.
“…[13][14][15][16][17][18][19][20][21][22] In none of the above cases, a definite magnetic solution was found feasible. For Co substitutions the experimental results are unambiguous over the fact that T C decreases as Co at.…”
First-principles, density-functional based electronic structure calculations are carried out for MgC͑Ni 1−x Co x ͒ 3 alloys over the concentration range 0 ഛ x ഛ 1, using Korringa-Kohn-Rostoker coherentpotential approximation method in the atomic sphere approximation. The self-consistent calculations are used to study the changes as a function of x in the equation of state parameters, total and partial densities of states, magnetic moment and the on-site exchange interaction parameter. To study the magnetic properties as well as its volume dependence, fixed-spin moment calculations in conjunction with the phenomenological Landau theory are employed. The salient features that emerge from these calculations are ͑i͒ a concentration independent variation in the lattice parameter and bulk modulus at x ϳ 0.75 with an anomaly in the variation of the pressure derivative of bulk modulus, ͑ii͒ the fixed-spin moment based corrections to the overestimated magnetic ground state for 0.0ഛ x ഛ 0.3 alloys, making the results consistent with the experiments, and ͑iii͒ the possibility of multiple magnetic states at x ϳ 0.75, which, however, requires further improvements in the calculations.
“…A small amount of unreacted graphite was found for the samples MgC(Ni 1jx Fe x ) 3 due to the excess of C utilized for its synthesis [1,4].…”
Section: Resultsmentioning
confidence: 99%
“…The preparation of the MgC y (Ni 1jx Fe x ) 3 (x = 0.01, 0.02, 0.1 and y = 0.8, 1.0) samples is described elsewhere [1,4]. We used 57 Fe to prepare the samples MgC y (Ni 0.99 Fe 0.01 ) 3 (y = 0.8, 1.0).…”
Section: Methodsmentioning
confidence: 99%
“…Early band structure calculations suggested the involving of magnetic interaction in the suppression of superconductivity in hole-doped MgCNi 3 [3]. In fact, hole doping quickly destroy the superconductivity in MgCNi 3 [1,4,5]. Some calculations [5][6][7] showed that hole doping of MgCNi 3 is accompanied by a reduction of the density of states at the Fermi level, which seems to be responsible for the reduced superconductivity, but magnetic ground states are only expected for high hole dopants (Fe, Co) [6] or absolute absence of C [8].…”
Low temperature Mössbauer experiments were performed in Fe-doped and in Cdeficiency MgCNi 3 . No magnetic moment was found for Fe in MgC(Ni 0.99 Fe 0.01 ) 3 sample and no magnetic hf field was observed at any temperature for all the samples. These results shown no evidence of magnetic fluctuation or magnetic ordering influencing the depress of superconductivity in hole-doped MgCNi 3 .
“…Based on a rigid-band picture, it is estimated that approximately 0.5 holes would make MgCNi 3 magnetic [4,6]. However, in experiments, where the required hole doping is accomplished via Fe or Co substitution in Ni sub-lattice of MgCNi 3 , the substituted alloy remains non-magnetic [7][8][9][10][11].…”
The effects of disorder and incipient magnetism in MgCðNi 1Àx T x Þ 3 (T Fe, Co or Cu) alloys are studied using coherent-potential approximation and Ginzburg-Landau coefficients. The first-principles, local-density-functional-based calculations for substitutionally disordered Fe and Co impurities in the Ni sub-lattice of MgCNi 3 , in low concentrations, show that incipient magnetism resides in these materials. The overestimation of the calculated magnetic properties points to the limitations of the local-density approximation. However, using a phenomenological approach based on Ginzburg-Landau coefficients and the fixed-spin moment method, we show that MgCðNi 1Àx T x Þ 3 alloys remain paramagnetic. At expanded volumes, we also find the possibility of a ferromagnetic state for MgCðNi 0:95 Fe 0:05 Þ 3 and MgCðNi 0:90 Co 0:10 Þ 3 alloys. r
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