Spin correlations and colossal magnetoresistance inHgCr2Se4

Abstract

This study aims to unravel the mechanism of colossal magnetoresistance (CMR) observed in n-type HgCr2Se4, in which low-density conduction electrons are exchange-coupled to a threedimensional Heisenberg ferromagnet with a Curie temperature TC ≈ 105 K. Near room temperature the electron transport exhibits an ordinary semiconducting behavior. As temperature drops below T * ≃ 2.1 TC, the magnetic susceptibility deviates from the Curie-Weiss law, and concomitantly the transport enters an intermediate regime exhibiting a pronounced CMR effect before a transition to metallic conduction occurs at T < TC . Our results suggest an important role of spin correlations not only near the critical point, but also for a wide range of temperatures (TC < T < T * ) in the paramagnetic phase. In this intermediate temperature regime the transport undergoes a percolation type of transition from isolated magnetic polarons to a continuous network when temperature is lowered or magnetic field becomes stronger.

Unconventional Temperature Dependence of the Anomalous Hall Effect in HgCr2Se4

“…In summary, we have measured electron transport properties in n-HgCr 2 Se 4 , a half-metallic FM semiconductor with extremely low electron densities [29,34]. This unique electronic structure enabled us to measure the low temperature corrections to longitudinal, OH and AH resistivities in the same samples for the first time.…”

“…Our measurements were performed on a set of n-type HgCr 2 Se 4 single crystals, which have a spinel structure (space group Fd3m) and ferromagnetic ground state with Curie temperature T C ≈ 105 K [28,29]. At liquid helium temperatures, the electron density n is in a range of 10 15 -10 18 cm −3 , several orders of magnitude lower than the density of Cr 3+ ions.…”

Stabilization and control of Majorana bound states with elongated skyrmions

“…In this paper, we show that elongated skyrmions, which can be stabilized in ordinary chiral magnets [26,[29][30][31][32][33], can act as an effective "quantum wire", and under the right conditions realize Kitaev's toy model [34], locally hosting a pair of Majorana bound states at its ends. It is known that such effective quantum wires can be also formed using a nonuniform magnetic field generated by an array of magnetic tunnel junctions (MTJs) [12].…”

Searching for Magnetar-powered Merger-novae from Short GRBS

“…If the total mass of binary neutron star system is small enough and the equation of state of nuclear matter is stiff enough, the merger of two NSs could leave behind an indefinitely stable or a supra-massive NS (Dai et al 2006;Gao & Fan 2006;Zhang 2013;Lasky et al 2014;Fryer et al 2015;Li et al 2016). Considering that before the merger the two NSs are in the Keplerian orbits, the newborn massive NS should be rapidly spinning near the breakup limit and may also carry a strong magnetic field B 10 14 G similar to that of known Galactic "magnetars" (Zhang 2013;Metzger & Piro 2014, and reference therein).…”