Metal-Insulator Transition and Giant Negative Magnetoresistance in Amorphous Magnetic Rare Earth Silicon Alloys

Abstract

Large negative magnetoresistance and anomalous magnetic properties are found in amorphous Si doped with magnetic rare earth ions near the metal-insulator transition. The resistivity below 50 K rises orders of magnitude above that of comparable composition nonmagnetic alloys and is strongly reduced by a magnetic field. Magnetization measurements show noninteracting moments at high temperature which develop antiferromagnetic interactions below 50 K. We suggest that these results are due to formation below 50 K of a dense concentration of magnetic polarons which localize conduction electrons. [S0031-9007(96)01722-X]

Large negative magnetoresistance in thiospinel CuCrZrS4

“…[3] It is interesting to notice that large negative MR with no magnetic phase transition has been reported in some magnetic semiconductors such as Gd 3-x S 4 [4] and amorphous Gd-Si. [5,6] In these materials, the resistance increases exponentially with decreasing temperature according to variable range hopping (VRH) [7] at low temperatures. Large negative MR is observed at the same time.…”

Variation of the density of states in amorphous GdSi at the metal-insulator transition

“…Near the critical doping level, ͑T =0͒ is very sensitive to the slight variations of x. This material has been extensively studied: its structure, 18 transport conductivity, 15,19,20 tunneling conductance, 17,21 specific heat, 22 magnetization, 23 infrared absorption, 24 spin polarization, 25 and the Hall effect, 26 have been investigated in detail. It has been shown that the magnetic field increases the conductivity while raising both the concentration of the free carriers and the density of states.…”

“…14 This approach eliminates undesirable scatter in the sample parameters and thus is preferable to studying a discrete set of samples. For this reason, magnetically doped amorphous materials, such as ␣ −Gd x Si 1−x (GdSi) and Tb x Si 1−x , 15,16 are particularly suited for the studies of the MIT. In these materials besides the structural disorder, there is an additional degree of disorder associated with random orientation of the ionic magnetic moments, which can be controlled by the applied magnetic field.…”

Large magnetic entropy and electron-phonon coupling in Gd-based metallic glass

“…9,10 This has been illustrated in Ce-based BMG and GdSi amorphous alloys. [11][12][13] Ce-based BMGs with excellent glass-forming ability have been extensively studied. 11 One of the important properties is the anomalous softening acoustic behavior, which is only observed in Ce-based amorphous alloys.…”