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We report on the nature of electron correlations in Fe1-xCoxSi (0.7

The critical magnetic properties of a non-centrosymmetric B20 cubic helimagnet Fe0.6Co0.4Si are investigated using magnetization isotherms. It belongs to the 3D-Heisenberg universality class with short range magnetic coupling as inferred from the self-consistent critical exponents beta = 0.411 +/- 0.003, gamma = 1.325 +/- 0.062, delta = 4.223 +/- 0.004 and alpha = -0.115 +/- 0.007 in combination with exchange interaction J(r) approximate to r-(4.88). Itinerant magnetic nature of the compound is realized by the Rhodes-Wholfarth analysis. Field-induced weak first (para?helical) to second (para?field-polarized) order transition is reported to occur at low critical field due to the weak spin-orbit coupling arising from the weak Dzyaloshinksii-Moriya interactions. Our study suggests the distinct phenomenological magnetic structures for Fe-based cubic magnets (Fe1-xCoxSi and FeGe) and MnSi which cause contrasting physical properties.

We report on the combined results of the structural, magnetic, transport and calorimetric properties of Mn5Si3-type hexagonal Gd5Sb3, together with ab initio calculations. It exhibits a ferromagnetic (FM)-like transition at 265 K, antiferromagnetic (AFM) Noel transition at 95.5 K followed by a spin-orientation transition at 62 K. The system is found to be in AFM state down to 2 K in a field of 70 kOe. The FM-AFM phase coexistence is not noticeable despite large positive Curie-Weiss temperature (theta(CW) = 223.5 +/- 0.2 K). Instead, low-temperature AFM and high-temperature FM-like phases are separated in large temperatures. Temperature-magnetic field (H-T) phase diagram reveals field-driven complex magnetic phases. Within the AFM phase, the system is observed to undergo field-driven spin-orientation transitions. Field-induced tricritical and quantum critical points appear to be absent due to the strong AFM nature and by the intervention of FM-like state between paramagnetic and AFM states, respectively. The metallic behavior of the compound is inferred from resistivity along with large Sommerfeld parameter. However, no sign of strong electron-correlations is reasoned from the Kadowaki-Wood's ratio A/gamma(2) similar to 1.9 x 10(-6) mu Omega . cm . (mol . K)(2) (mJ)(-2), despite heavy gamma. Essentially, ab initio calculations accounting for electronic correlations confirm AFM nature of low-temperature magnetic state in Gd5Sb3 and attainable FM ordering in agreement with experimental data.

Microstructure and magnetocaloric effect were investigated in Gd1-x(Si0.5Ge0.5)(x) alloys with x = 0.38, 0.41, 0.45, 0.47 and 0.50. The phase identification and compositional analysis were carried out by a combination of x-ray powder diffraction, scanning electron microscopy and electron probe microanalysis. The Gd-5(Si,Ge)(4) phase was found to have an orthorhombic Gd5Si4-type structure when the coexisting phase was Gd-rich (Gd5Si3-type) and a monoclinic Gd5Si2Ge2-type structure when the coexisting phase was Gd-depleted (Gd5Ge5-type). The magnetocaloric effect was found to depend on the volume fraction and the Si/Ge ratio of the ferromagnetic 5 : 4 phase in the above series of alloys. A maximum magnetocaloric effect ( Delta S) M of 14.3 J kg(-1) K-1 for a magnetic field change from 0 to 5 T was obtained for the x = 0.45 alloy.