Association

3.3. Experimental developments at the Oxide-MBE setup 43
Figure 3.8.: Geometrical arrangement of oxygen nozzles inside the Oxide-MBE. Drawing (a) illustrates
the bisection of gas supply with respect to the sample manipulator and the mass spectrometer.
A top view in drawing (b) illustrates the position of oxide reaction on the manipulator.
hanced magnetoresistance” 1 which established as the giant magnetoresistance (GMR) effect.
This discovery was awarded with the Nobel Prize for P. Grünberg and A. Fert in 2007. 219
In the Peter Grünberg Institut (PGI-6 “Electronic Properties”), the MBE system comprises
three UHV chambers and a drive-through fast load lock system (Fig. 3.7 I), which are connected
by a fully rotatable and heatable sample manipulator. First, a pre-chamber (II) allows
for a fast deposition of metallic layers (e. g. Al) and contains gas nozzles, by which the in situ
silicon oxidation or hydrogen termination with partial pressures up to the 10 -2 mbar regime
are conducted. Second, providing best vacuum conditions of ∼10 -11 mbar, the main deposition
chamber (III) is equipped with three electron beam evaporation guns which permits
one to evaporate up to five different target materials. The atomic flux rate can be monitored
parallel by two quartz crystal microbalance systems. Here, the magnetic oxide deposition
takes place under a meticulous control of Eu flux and oxygen partial pressure. Controlling
the crystalline surface structure during deposition is feasible by a RHEED system. Finally,
the analysis chamber (VI) contains the surface analysis tools, i. e. LEED for imaging the surface
reciprocal lattice and Auger electron spectroscopy for chemical surface investigations. In
order to match the special needs for the synthesis and investigation of ultrathin oxide films,
three special developments have been introduced into the system. Therefore we refer to it as
a specialized Oxide-MBE.
First, to allow for a meticulous control of the oxygen supply necessary for the magnetic oxide
synthesis, two nozzles of a symmetric circular shape (Fig. 3.7b) distribute the process O 2 gas
equally to a quadrupole mass spectrometer as well as to the surface of the sample. This local
gas supply provides the advantage that the remaining chamber is spared from gas adsorption:
the highly reactive Eu reservoir as well as filaments benefit from this.
The GMR uses the inter-layer exchange interaction between the adjacent magnetic layers separated by a
thin nonmagnetic spacer which favors an anti-ferromagnetic configuration of the magnetic layers. Due to spindependent
scattering in the three-layer system, the resistance of the antiparallel magnetic configuration in remanent
state is much larger than in a parallel configuration under external H field. Nowadays, this is the basis for
hard disk read heads or miniaturized H field sensors.