Competing localization and quantum interference effects in Fe_0.9Co_0.1Si

Abstract

Unusual magnetoresistance observed in weak itinerant ferromagnetic metal Fe0.9Co0.1Si is addressed. We invoke localization effects significantly contributing to the positive magnetoresistance apart from quantum interference effects (QIE), a new mechanism for magnetoresistance at low temperatures. QIE are dominant only at very low temperatures while localization effects are progressive out of the sub‐Kelvin domain. Dominance of localization effects in Kelvin range with increasing applied magnetic field is demonstrated. An unconventional effect of magnetic field on resistivity, favors a least dominant role of ferromagnetic correlations. The H–T phase diagram explore the regions of H3/2 (paramagnetic region) and QIE (Δσ ∝ H1/2) and its extension into the paramagnetic region. A new region of linear field dependence of MC (Δσ ∝ H) is also found and reported. Qualitative analysis of thermopower and its correspondence with electrical resistivity strengthens the concept that the same electrons are responsible for both electrical and magnetic properties. It is also reported that the onset of magnetic and QIE effects is well above TC.

Thermoelectricity in correlated narrow-gap semiconductors

“…While the size of the charge gap is insensitive to, e.g. dopings with up to 3% cobalt[70], dopings (T = Co, Rh) and also isoelectronic substitutions (T = Ru) of 10%, Fe 0.9 T 0.1 Si, induce itinerant ferromagnetism[98], concomitant with a large positive MR[98,101,171]. 9 The low-T upturn in the susceptibility of Ce 3 Bi 4 Pt 3 is not a property intrinsic to the bulk, as shown by neutron scattering measurement[63].…”

Quantum phase transition and non-Fermi liquid behavior in Fe1−xCoxSi (x⩾ 0.7)

“…Summarizing, the combined results of magnetization, specific heat, resistivity and thermoelectric power of Fe [20,41] and literature [12,[14][15][16][17][18]40]. Further, to throw more light on to the observed non-Fermi liquid behaviors in Fe 0.2 Co 0.8 Si and Fe 0.1 Co 0.9 Si, muon spin relaxation and physical properties measurements down to ultra low-temperatures are highly desirable.…”

Thermoelectricity in correlated narrow-gap semiconductors

“…The MR reported by Otha et al [169] for FeSi is positive up to 16T for all temperatures, but samples with lower RRR show a less positive MR; Lisunov et al [170] found a positive signal up to 35T; more recently, Sun et al [123] reported for 8T a sign change from MR> 0 at low temperatures to MR< 0 above 70K that interestingly correlates with a maximum (minimum) in the Nernst (Hall) coefficient, while the absolute value of the magnetoresistance is much smaller than in older experiments. While the size of the charge gap is insensitive to, e.g., dopings with up to 3% cobalt [70], dopings (T=Co, Rh) and also isoelectronic substitutions (T=Ru) of 10%, Fe 0.9 T 0.1 Si, induce itinerant ferromagnetism [98], concomitant with a large positive MR [98,101,171].…”