Evidence for Itinerantd-Electron Ferromagnetism

Abstract

We describe here a metallic ferromagnetic system Fe1 Co S2 and Co1 &Ni S2 that appears to have a single doubly degenerate band. The electrons in the band are itinerant as manifested by metallic electrical conductivity, but the magnetic moment is that of the isolated ion.For several decades localized as opposed to itinerant-electron ferromagnetism in metals has been investigated theoretically. ' However, experimental systems on which to base theoretical models of band ferromagnetism are often complicated by the presence of composite bands as, for example, in the elemental transition metals which are comprised of overlapping broad s and narrow d bands. Such quantities as density and itinerancy of d electrons, magnetization of the & electrons, and the magnitude of +-d exchange are difficult to measure directly. The compounds to be discussed appear to avoid the complicating features introduced by the presence of such & electrons.All transition metal disulfides, FeS, through ZnS2, crystallize in a cubic pyrite structure in which the cations are in face-centered positions.The physical properties of the series' are summarized in Table I. Each successive member of the series represents the progressive addition of one d electron. In much of this series, a continuous range of solid solutions of adjacent members, e.g. , Fe1 xCoxS2 and Co1 &Ni~S2 for 0 &x~1 , can be formed. 3 The unit cell dimension increases monotonically with increasing atomic number of the cation. These solid solutions are metallic conductors' (Fig. 1) except for dilute concentrations (&0.1%) of CoS2 in either FeS, or NiS2. Since the beginning and end members of the series are both semiconducting while all other members (except near NiS, ) show metallic conductivity, it is not inconsistent to conclude that Table I. Magnetic and transport properties of pyrite compounds. FeSs Temp. independent paramagnetic -6 X = 0.31 + .04 x 10 emu/gm Semiconductor M = 0.92 + .05 ev M 0.96 + .02 ev 6 2g CoS~Ferromagnetic =0. 9~~T = 120K Metallic Plasma Edge

Highly Spin-Polarized Conducting State at the Interface between Nonmagnetic Band Insulators:LaAlO3/FeS2(001)

“…Figure 4 shows the spin density profile revealing that the magnetic moment comes mostly from the Fe sites in the FeS 2 -1 layer, whereas the magnetization in the rest of the structure is negligible. The induced moment is 0:13 B per interface Fe, which is remarkably consistent with what is found experimentally for bulk Fe 1Àx Co x S 2 with x ¼ 0:16 [22], corresponding to the charge transfer of 0:16e found in our interface calculations. Spin-polarized calculations for the FeS 2 -vacuum slab and the heterostructure with 2 u.c.…”

“…Such an interface can be realized by pairing LaAlO 3 with the diamagnetic band insulator FeS 2 , commonly known as pyrite. FeS 2 begins a series of pyrite-structure disulfides covering the late half of the 3d elements all the way to ZnS 2 , each displaying properties distinct from its neighbors [22]. In particular, CoS 2 has one more d electron per formula unit than FeS 2 , making it an itinerant ferromagnetic metal.…”

Thermodynamics of the ferromagnetic phase transition in nearly half metallic CoS2 at high pressures

“…[2] that magnetic and electric properties indicate to be itinerant in nature [2,3,4,5,6]. Upon entering the ferromagnetic state CoS 2 becomes a nearly half metal with a significant decrease in the density of states at the Fermi level that is reflected in an increase in the resistivity below T c [7,8].…”

Evidence of kinetic arrest in Se doped CoS2

“…paramagnetic semiconductor to ferromagnetic metallic behaviour [3], superconductivity [4], metal-insulator transition [5,6], quantum criticality [7], giant magnetoresistance [8,9] etc. Among these, the compound CoS 2 is of interest due to itinerant electron metamagnetism [10].…”