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Facilities and Tools

  • Vector Magneto-optic Kerr Effect (MOKE)

Precise measurement of the longitudinal, transverse and polar (out of plane) components of the magnetisation in ultrathin films at room temperature in applied magnetic fields of up to 2 Tesla. (Currently the apparatus is being upgraded to allow the Kerr rotation and ellipticity to be determined.)

  • Scanning Kerr Microscope

Uses the longitudinal magneto-optic Kerr effect to collect magnetic information from micron sized area on sample surface. Can be used in scanning mode to collect domain images, in time resolved mode to collect switching information, and in a combination of the two. Laser: Laser Quantum solid state, diode pumped single mode ring laser, 532 nm, 100 mW. Sample mounted on Burleigh Inchworm XY stage, motion controllable via PC with approx. resolution of 0.1 micron (x-axis), 0.5 micron (y-axis). Laser spot size: 1.30 microns for 20x lens, 0.764 microns for 50x lens. Electromagnet: (a) soft iron core electromagnet with maximum field 1.2 kOe, suitable for producing static or slowly swept (< 1 kOe/s) fields, (b) laminated core (stack of Fe-Si layers) electromagnet suitable for production of sinusoidally swept fields in the range DC up to 5 kHz, maximum approx. 100 Oe at 5 kHz, (c) small ferrite E-core pair with 6-turn coils suitable for production of sinusoidally swept fields in the range DC up to 30 kHz. Differential photodetection with either Si avalanche photodiodes (risetime ~5 ns, bandwidth 100 MHz) for dynamic measurements or large area photodiodes for low intensity and/or quasi-static measurements. Data collection: Agilent Infiniium oscilloscope, bandwidth 500 MHz, 2 GSamples/s.

  • Low Temperature MOKE

Variable temperature (3.8 − 300 K) in plane Kerr measurements in a 1 Tesla field range.

  • Low Temperature Magnetoresistance (MR)

Angular dependent MR measurements in an applied magnetic field up to 1 Tesla and for temperatures between 3.8 K and room temperature.

  • SQUID

Quantum Design MPMS/XL.

  • Photon Excitation

Versatile experimental set-up used to determine the helicity dependent photo-current for various magnetic field orientations, strengths (max~2 Tesla), temperatures (3.8 − 300 K) and photon energies.

  • Electroluminescence

This is a set-up to investigate spin injection from a ferromagnetic metal into a semiconductor, based on the spin-LED concept.  The set-up determines the degree of circularly polarized light (and hence the spin-polarization of the injected current) for different magnetic fields, wavelengths of the emitted light and for different driving biases.

  • Quantum Conductance

"Mechanical break junction method" to investigate the conductance of nanowires. Conductance and bias measured with a digital storage oscilloscope in magnetic field of up to 10 mT.

  • Brillouin Light Scattering (BLS)

Measurement of the frequency shift of light inelastically scattered from magnons, 300 mW Ar+-laser (λ = 514nm), Tandem Fabry-Perot interferometer, 10 kOe ex situ magnet.

  • In situ MR Chamber

Base pressure: 4x10-10 mbar, 4 e-beam evaporators (various materials e.g. Fe, NiFe, Au, etc.), variable sample temperature 77 − 900 K, in situ MR apparatus (2.5 kOe magnet & multi-pin probe), Physical Electronics 04-162 Sputter Ion Gun, SPECS 4 grid ErLEED 150 LEED/AES system, thickness monitor.

  • Spin Detector Chamber

Base pressure: 1x10-10 mbar maintained by a Varian ion pump, a diffusion pump and a Varian turbo-molecular pump combined with a TSP, dual detector (Faraday cup/electron multiplier) quadrupole mass spectrometer, 3 MBE evaporators (one of them is an OMICRON EFM3), Ar+ sputter gun, ultra sensitive transverse in situ MOKE, SPECS 4 grid ErLEED 150 LEED/AES system, VG Microtech electron gun with high spatial resolution (200 nm), in situ measurement of the spin polarisation of electrons elastically or inelastically scattered from magnetic thin films by means of a retarding potential 25 kV UHV compatible Mott polarimeter with an efficiency of 1.6x10-4.

  • Spin Valve Chamber

Base pressure: 3x10-10 mbar maintained solely by means of a Varian diode ion pump, Auger electron spectrometer (AES) using a cylinder mirror energy analyser (CMA), VG Microtech reflection high energy electron diffraction (RHEED) system, four e-beam sources suitable for the growth of transition metals (such as Au, Cu, Fe, Ni, Co, NiFe, etc.), sample transfer system for quick substrate input and sample retrieval after growth.

  • Dynamic Kerr Chamber

Base pressure 5x10-10 mbar. Currently under development. Will operate as two separate sub-chambers: (1) scanning tunnelling microscopy chamber with 150 l/s ion pump and 50 l/s turbo-molecular pump, (2) thin film growth chamber with two e-beam evaporators (Fe and Cr), variable sample temperature (77 − 900 K), Physical Electronics 04-162 sputter ion gun, LEED and MOKE characterisation tools, 500 l/s ion pump, 140 l/s turbo-molecular pump and Ti sublimation pump. Full load lock and sample transfer system.

  • Multiple Technique Chamber

Base pressure: 2x10-10 mbar, 7 e-beam evaporators (Au, Co, Fe, Cr, Si, Cu, NiFe), variable sample temperature up to 900 K, Physical Electronics 11-085 Ar+ sputter gun, Spectra Vacscan, VG Microtech LEG 110 e--gun RHEED, VG Microtech RVL 900 LEED/AES system, Burleigh STM, in-situ MOKE, in-situ BLS, in-situ 2.5 kOe magnet.

  • Focused MOKE (FMOKE)

MOKE measurements with high sensitivity and resolution, enable to measure sigle magnetic structures with down to 4um beam spot size at room temperature. 30mW HeNe laser, AC fields of up to 600Oe at a frequencies of ~10Hz, 0.1um accuracy of XY stage.

  • DC/Rf Magnetron Sputtering Chamber

sputter

Figure 1: DC/Rf Magnetron Sputtering Chamber (left) with adjunct Oxidation/Ion milling Chamber.

 

 

 

 

 

 

 

 

Sputtering, discovered apparently in the 1850's, is an older deposition technique but with the advent of modern ultra high vacuum (UHV) technology it is now possible to sputter deposit films of extremely high quality and purity.

The system is a CEVP (now Surrey Nanosystems) magnetron sputtering chamber along with a load lock and an oxidation/ ion milling chamber. The load lock is capable of holding four 3" sample holders and is used to both speed up pump down times and to keep the main chamber under UHV condition. The load lock also contains a heat gun for degassing the samples and the lock itself, again reducing pump down times. The load lock is pumped by an ATP150 turbo pump backed by a dry pump and can reach an ultimate pressure of 5 x 10e-8 mbar.

The manipulators at either end of the system can move the sample holders between the three chambers when the gate valves are open.

The sputtering chamber has six interchangeable targets which are capable of depositing from both DC sputtering and by radio frequency (Rf) enabling both conducting and non conducting materials to be deposited respectively. The sample stage can be rotated and magnetic fields up to 450 Oe are able to be applied during deposition to align magnetic grains inducing thereby an uniaxial magnetic anisotropy. The chamber has a base pressure of ~1 e-9 mbar and deposition occurs at an Ar+ partial pressure of around 1e-3 mbar. The sample stage can be rotated during growth to ensure even deposition of the films; this is needed mainly for fast growth as the targets are slightly angled to the substrate causing otherwise preferential deposition on one side. The sample stage can be heated to temperatures in excess of 600 °C either during growth or in vacuum to anneal or de-cap substrates. Reverse sputtering for surface cleaning is also possible. The chamber is able to grow around 100 nm in an hour. The main chamber is pumped by a cryo-pump which operates at 10 K and is able to reach ultimate pressures of 1 e-9 mbar.

The oxidation chamber has two uses, it is used for oxidizing films, i.e. for growing oxides, and for milling materials. The ion miller works in almost exactly the same way as the sputtering chamber except with the sample replacing the target material. The plasma is usually comprised of argon, although oxygen or nitrogen are also possible, and is created at the top of the chamber where there is a Rf gun. For oxidizing films an oxygen plasma is used and a choice of accelerator grids can either accelerate ionised oxygen at the sample or allows only neutral oxygen to bombard it, thus eliminating any unwanted reactive ion etching. The milling chamber is pumped by an ATP400 turbo pump backed by a dry pump and is able to reach ultimate pressures of ~5 e-8 mbar.

The system is designed to grow complex multilayers, consisting of magnetic and non-magnetic metals as well as insulators (oxides) either by single evaporation or co-evaporation for alloys. The deposition targets are at the top, facing downwards (Fig. 1). The substrate is positioned at the bottom on a rotating stage and between an electro-magnet. The deposition rates are calibrated and computer controlled to almost 0.1 nm accuracy. Thin films and devices in conjunction with patterning techniques, such as e-beam and photo lithography, are strictly grown for subsequent ex-situ measurements or other purposes. In addition, the oxidation/ion milling chamber makes use of different gases for oxidation and/or ion/atom source milling of heterostructures for device production.