Quantum phase transition and non-Fermi liquid behavior in Fe_1−xCo_xSi (x⩾ 0.7)

Abstract

We report on the nature of electron correlations in Fe Co Si ([Formula: see text]) using combined results of magnetization, specific heat and transport properties. Doping driven quantum critical point is observed to occur at [Formula: see text]. The magnetically unstable regime is identified to be centered around [Formula: see text] [[Formula: see text]]. The emergence of non-Fermi liquid behaviors in x = 0.8 (near to ferromagnetic quantum critical point) and x = 0.9 (disorder-induced) compositions are discussed on the basis of the power-law dependence of susceptibility [Formula: see text] ([Formula: see text] for x = 0.8 and 0.55 for x = 0.9), specific heat [Formula: see text] ([Formula: see text] for x = 0.8 and 0.9) and resistivity [Formula: see text] ([Formula: see text] for x = 0.8 and 1.38 for x = 0.9). Further, a comprehensive classification of doping dependent physical properties of Fe Co Si is presented in the revisited temperature-composition (T-x) phase diagram.

Magnetic behavior of Ru substituted skyrmion metal MnSi

“…Ever since the discovery of Kondo-like correlated narrow gap semiconductor properties in FeSi [11][12][13][14][15][16], akin to some of the rare-earth based systems, the transition metal monosilicides have become an interesting topic of research. The unscreening of Fe magnetic moments by a substituting magnetic transition element for Fe in FeSi, has led to the chiral magnetism in Fe 1−x Co x Si [17][18][19][20][21][22][23] and Fe 1−x Mn x Si [24][25][26]. Further, QPTs in the end compounds of Fe 1−x Co x Si [22] and doped MnSi [27] have been reported.…”

Critical exponents and universal magnetic behavior of noncentrosymmetric Fe0.6Co0.4Si

“…In Fe 1−x Co x Si, the end compounds FeSi and CoSi are non-magnetic while the intermediate compositions are magnetic. Previous reports revealed the concentration (doping) dependence of the physical properties of Fe 1−x Co x Si, namely, correlated Kondo insulator behavior in FeSi [6][7][8][9], metal to insulator transition in low-doped alloys [10], dilute magnetic semiconductor behavior with localization and quantum interference effects [11,12], pressure effect [13,14], pseudogap metals with non-Fermi liquid behavior [15] and pseudogap semimetal behavior in CoSi [16,17]. On the other hand, the recent discovery of skyrmion lattice in thin samples/films of Fe 1−x Co x Si with 0.2 x 0.5 has created renewed interest in these alloys [18,19].…”

“…However, they show contrasting electrical and thermodynamic behavior in response to varying temperature and fields. Comparing the physical properties; (i) MnSi shows a pronounced peak in specific heat [20,21,23] at magnetic ordering temperature T c whereas the same is almost absent in Fe 1−x Co x Si [15], (ii) MnSi is a metal with low residual resistivity ρ 0 [24] while ρ 0 of Fe 1−x Co x Si is few hundreds of µΩcm [25], (iii) MnSi exhibits negative magnetoresistance (MR) and negative magnetic-entropy change in response to fields [26,27] whereas Fe 1−x Co x Si compounds show positive MR [11,12,25] and no significant entropy change in presence of fields [15]. The doped MnSi (Mn 1−x Fe x Si and Mn 1−x Co x Si) is reported to show quantum phase transition (QPT) [28,29].…”

“…The doped MnSi (Mn 1−x Fe x Si and Mn 1−x Co x Si) is reported to show quantum phase transition (QPT) [28,29]. Recently, Fe 1−x Co x Si is reported to exhibit doping-driven QPT [15] alongside the pressure-induced QPT [14]. On the other hand, the pressureinduced quantum criticality in MnSi is still an open question [30].…”

“…The present work throws more light onto an issue whether Fe 1−x Co x Si and MnSi together come under a single class in terms of underlying magnetic interactions. Towards this, we have carried out an in-depth critical magnetic properties analysis of a specific compound Fe 0.6 Co 0.4 Si, a representative of Fe 1−x Co x Si with the highest magnetic ordering temperature T c (∼54.0 K [15,25,34]). We show that the compound belongs to three dimensional (3D) Heisenberg type universality class associated by short range magnetic coupling.…”