Fig 4.1 Argon pressure optimization
4.1.2 Deposition
rate calibration
In order to determine the deposition rate of the different targets
in use, single layer samples were deposited onto slide glass substrates
at different powers during a predetermined period of time. The base
pressure was better than 5*10-8 Torr and the Ar pressure 5 mTorr.
Prior to the deposition, the time needed to give an approximate thickness
of 1000Å of the films was roughly estimated. When the depositions
were finished, the thickness of each sample was measured using a surface
profilometer, Surfcorder ET-30. With the results from these measurements
(Fig 4.2) the relation between sputter power and deposition rate could
be determined (Table 4.1).
Fig 4.2 Deposition rate measurements
Any influence of the coercivity by possible Pd contamination of the TbFeCo target during deposition was examined, but no change in coercivity could be found. It was assumed that the distance between the Pd and TbFeCo target was sufficiently large enough to avoid any contamination of Pd.
4.1.3 Multilayer Structures
In order to measure both magnetic and magneto-optical properties two
different types of multilayers were deposited. For magnetic properties
500-550Å thick multilayers were deposited onto cover glass substrates.
To avoid oxidation of the multilayers, primary the Tb atoms, a protective
layer of 30 Å Pd was deposited on top of the multilayers (Fig 4.3a).
When fabricating samples for magneto-optical examinations, slide glass
substrates were used. To obtain maximum reflectivity a reflective layer
of 750Å Pd was first deposited on each substrate. Then the multilayers
with a thickness of 250-300Å (Fig 4.3b) were deposited. To be able
to measure the intrinsic magneto-optical properties no protective layer
was grown.
Fig 4.3 multilayer structures
The multilayers were grown with the thicknesses presented in table 4.2.
TbFeCo single layers were also deposited.
4.2 Measurements
Due to the lack of protective layer on top of the magneto-optical samples
they could very easily be oxidized and therefor the magneto-optical properties
had to be measured right after the samples were taken out of the deposition
chamber. Magneto-optical measurements were made using polar Kerr looper[3.5]
at ?=830nm and Kerr spectrometer[3.4] in a photon energy range of 1.4eV-6.8eV(?=180-900nm).
The magnetic properties were measured using polar Kerr looper[3.5], VSM[3.2], Torque magnetometer[3.3], AGFM[3.6] and MFM[3.8].
In order to investigate the sharpness of the interfaces in the multilayers
and existence of any crystal structure within the Pd layers x-ray diffraction
analysis[3.7], ?-2? mode with Co-K? ?=1.79Å, was performed.
4.3 Disc Fabrication
To test the recording performance of TbFeCo/Pd as MO recording media,
some discs were fabricated onto pregrooved 128 MB (? 0.4 Gbits per square
inch) plastic 3.5? diameter substrates. TbFeCo single layer, TbFeCo 30Å/Pd
3Å and TbFeCo 50Å/Pd 6Å were used as MO-layers in the
different discs. The disc structure is shown in Fig 4.4.
Fig 4.4 Disc structure
The discs were tested in a disc tester, Nakamichi OMS-2000, at a wavelength of 780nm. The recorded bits were also examined using MFM and surface analysis was performed with AFM[3.8].