Giant magnetoresistance and tunnel magnetoresistance effects in FeCoGd-based spin valves and magnetic tunnel junctions

Abstract

Giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) were studied in spin valves of FeCo∕Cu∕(FeCo)1−xGdx and magnetic tunnel junctions of FeCo∕AlO∕(FeCo)1−xGdx, respectively. When the FeCoGd layer is thick enough, both GMR and TMR ratios change their signs from positive to negative at the compensation composition with 0.293⩽x0⩽0.337 as the Gd content is increased. This scenario is originated from a competition of rare-earth and transition-metal spins in FeCoGd layers with antiferromagnetic coupling. Accordingly, it is deduced that in the FeCoGd layer the spin polarizations PN of electrons at the Fermi level and tunneling spin polarization PTSP are negative and positive for x<x0, respectively, and vice versa for x>x0.

Pseudo Spin Valves Using a (1 1 2)-Textured D0$_{22}$ Mn$_{2.3-2.4}$Ga Fixed Layer

“…Finally, a high-resistance state, corresponding to parallel alignment of the CoFe and MnGa, is once again achieved at negative saturation. This situation is similar to Fe/Cu/GdCo spin valves [Yang 2006] and FeCoGd/AlO/FeCo tunnel junctions [Bai 2008], where a negative GMR is also observed. In addition to the dominant negative GMR contribution, a small peak in the resistance near zero field is also observed, and is most likely due to either anisotropic MR in the transverse measurement geometry or a small positive GMR component.…”

Magnetoresistive effects in perpendicularly magnetized Tb-Co alloy based thin films and spin valves

“…From the above information on the magnetic properties of the single ferromagnetic layer we have grown three types of spin valve structures (thicknesses in nm, concentrations in atomic percent) (Tb 12 (20) (Tb dominant alloy/Cu/Tb dominant alloy). Those structures have then been patterned using optical lithography to create devices as presented on the inset of Fig.…”

Enhanced exchange and reduced magnetization of Gd in an Fe/Gd/Fe trilayer

“…2 The alloys of RE and TM can also lead to negative mangetoresistance (MR) in a structure, as the alignment of its magnetic moment with the external magnetic field will depend on the proportion of RE and TM. Typical examples for this are the Gd 1−x Co x and Gd 1−x (CoFe) x alloys, [3][4][5] whose magnetic moment and spin polarization can be adjusted with the composition. 6 Other recent applications of REs and their alloys are the reduction of spin-transfer noise in reading heads, 7 tuning the resonance of a magnetic domain wall, 8 and the nucleation and characterization of an in-plane magnetic domain wall.…”