Electronic band effects on the spin disorder resistivity of Gd 4 (Co 1− x Cu x ) 3 compounds

J. Phys.: Condens. Matter

Lima

et al. 2010

Self Cite

The specific heat (C(T)) of Gd₄Co₃ was measured in the temperature range 2-300 K and its magnetic contribution (C(m)(T)) was determined using a new method that fits the electronic specific heat coefficient (γ) and the Debye temperature (θ(D)) by constraining the resulting magnetic entropy (S(m)(T)) to saturate at temperatures far above the Curie temperature (T(C)). C(m)(T) exhibits a low-temperature bump originating from thermal excitation of gapped spin waves, which is responsible for pronounced peaks, at ≈35 K, in both C(m)/T and the temperature derivative of the magnetic contribution to electrical resistivity (dρ(m)/dT). Apart from in the vicinity of T(C), an excellent global correlation was found between C(m)/T and dρ(m)/dT. Our results provide strong support for the consistency of the new method proposed for the determination of C(m)(T) and rule out any major role of short-range order on Gd moments or d-electron spin fluctuation effects in the paramagnetic phase. A comparative analysis with other methods used in similar compounds points to the need for a better evaluation of C(m)(T) in such compounds, especially in the magnetically ordered phase, where a deficient evaluation of C(m)/T has a larger impact on the S(m)(T) curve.

Section: Methods Model Fixed Parametersmentioning

confidence: 94%

Specific heat of Gd₄Co₃

J. Phys.: Condens. Matter

Lima

et al. 2010

Self Cite

“…The decreasing role of Co 3d electrons with the progressive substitution of Co for Cu, evidenced by a strong reduction in the spin disorder resistivity and the Co magnetic moment, is seen to be crucial for the existence of such a low temperature maximum in S(T) for In Gd-Co compounds, as the Co: Gd concentration ratio increases, the itinerant character of the magnetism is reinforced, whereas compounds with a low Co: Gd concentration ratio are expected to exhibit a magnetic behavior much closer to the 4f localized magnetism typical of rare earths. 7 This stresses the important role played by 3d-band electrons in both the magnetic state and in the strong s-d electron scattering. It orders ferrimagnetically below T C % 220 K 2-5 with the Co magnetic moments antiparallelly coupled to those of Gd and exhibits a large magnetocaloric effect with negligible hysteretic loss.…”

mentioning

confidence: 71%

“…The resulting ingots were then encapsulated in quartz tubes, under an argon atmosphere, and annealed at 600 C for 2 h, then at 635 C for 24 h and at 650 C for 48 h. X-ray diffraction on the annealed materials revealed a single phase with the Ho 4 Co 3 crystal structure. 7 Besides, in the isostructural nonmagnetic Y 4 Co 3 compound where these effects would be free of any type of suppression by an internal magnetic field, no maximum in S(T) is observed in the same low temperature range. Figure 1 shows the temperature dependence of the thermoelectric power of all of the studied compounds.…”

Section: Methodsmentioning

confidence: 93%

“…7 The changes in electron band structure may explain why no maximum is observed in the thermoelectric power of Gd 4 Co 3 . 7 The changes in electron band structure may explain why no maximum is observed in the thermoelectric power of Gd 4 Co 3 .…”

Section: ð þmentioning

confidence: 99%

“…It orders ferrimagnetically below T C % 220 K 2-5 with the Co magnetic moments antiparallelly coupled to those of Gd and exhibits a large magnetocaloric effect with negligible hysteretic loss. 7 This motivated us to study the effects on the thermoelectric power of such band structure changes. 7 This stresses the important role played by 3d-band electrons in both the magnetic state and in the strong s-d electron scattering.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Thermoelectric power of Gd4(Co1-xCux)3 compounds

Journal of Applied Physics

Braun

et al. 2011

We report results of thermoelectric power measurements (S(T)) in ferrimagnetic Gd 4 (Co 1-x Cu x ) 3 compounds with x ¼ 0.05, 0.1, 0.2, and 0.3, in the temperature range 8-300 K. Whereas in Gd 4 Co 3, S(T) is always negative, for x > 0 the substitution of Co for Cu gives rise to the appearance of a low temperature positive maximum in S(T) at around 30 K. Based on our previous study of these compounds, we argue that this maximum in S(T) originates from electron-magnon scattering and is sensitive to electron band structure changes resulting from the substitution of Co for Cu and the accompanying reduction in the ratio between the electron-magnon and the electron-phonon scattering strengths. The decreasing role of Co 3d electrons with the progressive substitution of Co for Cu, evidenced by a strong reduction in the spin disorder resistivity and the Co magnetic moment, is seen to be crucial for the existence of such a low temperature maximum in S(T) for x > 0.

Thermoelectric Power of Gd4(Co-A)3 Compounds (A = Cu, Pt)

Braun

et al. 2012

MSF

We report on a comparative study of thermoelectric power measurements (S(T)) in ferrimagnetic Gd4(Co1-xAx)3 compounds with A = Cu, Pt, in the temperature range 8 K – 300 K. Whereas in Gd4Co3S(T) is always negative, for x > 0 the substitution of Co for Cu/Pt gives rise to the appearance of a low temperature positive maximum in S(T) at around 30 K. Based on our previous study of Gd4(Co1-xCux)3 compounds, we argue that this maximum in S(T) originates from electron-magnon scattering and is sensitive to electron band structure changes resulting from the substitution of Co for Cu/Pt and the accompanying reduction in the ratio between the electron-magnon and the electron-phonon scattering strengths. The decreasing role of Co 3d electrons with the progressive substitution of Co for Cu/Pt, evidenced by a strong reduction in the spin disorder resistivity and the Co magnetic moment, is seen to be crucial for the existence of such low temperature maximum in S(T) for x > 0. It is seen that the substitution of Co for Pt leads to higher values of the amplitude and temperature of the positive maximum in S(T) than the substitution of Co for Cu.