Magnetoresistance from quantum interference effects in ferromagnets

Abstract

The desire to maximize the sensitivity of read/write heads (and thus the information density) of magnetic storage devices has stimulated interest in the discovery and design of new magnetic materials exhibiting magnetoresistance. Recent discoveries include the 'colossal' magnetoresistance in the manganites and the enhanced magnetoresistance in low-carrier-density ferromagnets. An important feature of these systems is that the electrons involved in electrical conduction are different from those responsible for the magnetism. The latter are localized and act as scattering sites for the mobile electrons, and it is the field tuning of the scattering strength that ultimately gives rise to the observed magnetoresistance. Here we argue that magnetoresistance can arise by a different mechanism in certain ferromagnets--quantum interference effects rather than simple scattering. The ferromagnets in question are disordered, low-carrier-density magnets where the same electrons are responsible for both the magnetic properties and electrical conduction. The resulting magnetoresistance is positive (that is, the resistance increases in response to an applied magnetic field) and only weakly temperature-dependent below the Curie point.

Spin-glass ground state inMn1−xCoxSi

“…Despite different trends in the two experimental curves (λ = f (P ) and λ = f (x)) (maybe due to disorder, electron doping in Mn 1−x Co x Si , uncertainty of the applied pressure or intrinsic error bars) the shortening of the helix is the signature of a smooth transition of magnetic exchange from a positive to a negative MnCoSi [14] FeCoSi [10] MnNiSi this work MnFeSi [13] MnCoSi [20] CrMnSi this work CrMnSi [20] MnFeSi [20] T value that progressively drives the system in a more antiferromagnetic configuration. Because of the very low symmetry of the Mn site and its high coordination (3 different distances of the 7 first neighbors), the exchange is very sensitive to displacive and chemical disorder.…”

“…Fe x Co (1−x) Si exhibits itinerant helimagnetic metallic behavior like MnSi for 0.4 < x < 0.9 (T c = 60K for x = 0.6) although the two end-compounds FeSi and CoSi do not exhibit any magnetic order [9][10][11][12]. Doping FeSi with Mn has revealed that the unscreened Kondo effect was at the origin of non-Fermi liquid behavior [13].…”

Magnetic field effect on quantum corrections to the low-temperature conductivity in metallic perovskite oxides

“…For instance, recently Manyala et al have reported a positive MR at low temperature for the Fe 1−y Co y Si system, and they attributed it to the effect of the applied field on the REEI contribution. 3 Several analyses of the low-temperature transport properties through QCC have also been performed in ferromagnetic oxide compounds. In particular, there are recent reports on the La 2/3 Sr 1/3 MnO 3 system 4,5 suggesting the presence of these quantum effects.…”

Large anomalous Hall effect in a silicon-based magnetic semiconductor

“…This means that by examining the transport and magnetic behavior across the Fe 1−x,y Mn x Co y Si series, we can study the continuous evolution from a classic weak itinerant magnet, to a metallic paramagnet, to a Kondo (or strongly correlated) insulator, and finally a fully polarized itinerant magnetic metal 7,9,12 all without a change in crystal structure (see Fig. 1).…”