R. Guerrero

High bias voltage effect on spin-dependent conductivity and shot noise in carbon-doped Fe(001)∕MgO(001)∕Fe(001) magnetic tunnel junctions

Low temperature (10K) high voltage bias dynamic conductivity (up to 2.7V) and shot noise (up to 1V) were studied in epitaxial Fe(100)∕Fe–C∕MgO(100)∕Fe(100) magnetic tunnel junctions as a function of the magnetic state. The junctions show large tunnel magnetoresistance (185% at 300K and 330% at 4K). Multiple sign inversion of the magnetoresistance is observed for bias polarity when the electrons scan the electronic structure of the bottom Fe–C interface. The shot noise shows a Poissonian character. This demonstrates a pure spin-dependent direct tunneling mechanism and validates the high structural quality of the MgO barrier.

Very low 1/f noise at room temperature in fully epitaxial Fe/MgO/Fe magnetic tunnel junctions

We report on room temperature 1∕f noise in fully epitaxial Fe (45nm)∕MgO (2.6nm)∕Fe (10nm) magnetic tunnel junctions (MTJs) with and without carbon doping of the Fe∕MgO bottom interface. We have found that the normalized noise (Hooge factor) asymmetry between parallel and antiparallel states may strongly depend on the applied bias and its polarity. Both types of MTJs exhibit record of low Hooge factors being at least one order of magnitude smaller than previously reported.

Unusual magnetic susceptibility and magnetoresistance in [Fe∕Cr(001)]10 multilayers at low temperatures

Transport and magnetic properties near a field-induced orientation phase transition (OPT) from the easy to the hard axis in the magnetization of antiferromagnetically coupled epitaxial [Fe∕Cr(100)]10 multilayers have been studied. It was found that in the vicinity of the OPT both the amplitude of the magnetic susceptibility anomaly and the relaxation rate of the magnetoresistance change dramatically below a few Kelvin. These observations, together with the previously observed strong reduction of zero-field magnetic losses at temperatures below 5–7 K, indicate a qualitative transformation of the magnetic dynamics in Fe∕Cr multilayers at very low temperatures.

Complex magnetic response in magnetic tunnel junctions determined via magnetic and transport measurements

Abstract : We have studied the low frequency complex magnetization dynamics in Co/Al2O3/Ni80Fe20 magnetic tunnel junctions (MTJs) at temperatures between 4.2K and 300K. The measurements were carried out by using two different experimental techniques. The first method probes directly magnetic properties via DC magnetization and AC susceptibility while the second one measures AC magnetization dynamics of the ferromagnetic electrodes near the cross area which is related to the tunnelling resistance.

Low frequency magnetic noise in epitaxial antiferromagnetically coupled Fe/Cr multilayers

Abstract For antiferromagnetically coupled epitaxial [Fe/Cr(0 0 1)] 10 multilayers we detected a strong enhancement of the magnetism-related electrical noise in the vicinity of the orientation transition between the easy and hard axes. Our measurements are performed at different temperatures and we also identified the noise caused by depinning of domain walls (DWs). We are able to detect and follow in real time the motion of rather extended (of the order of 100 μm ) DWs by comparing the magnetic noise in the presence and absence of a DC transport current, respectively. The presence of large and small ( μm ) DWs is confirmed by magnetic force microscopy images obtained at room temperature.