Sample Environment at XMaS

Index

Sample Holders and Goniometers

High and Low Temperatures

Magnetic Fields

Electric Fields

Custom Sample Environments

Sample Holders and Goniometers

Sample Goniometers

Room temperature sample holders must fit into the standard Huber range of goniometers.

Low and High Temperatures

10 K - 300 K APD / ARS DE202 G

The ARS DE202G is a closed cycle cryostat which uses high pressure helium gas to produce cooling down to 10 Kelvin. A helium compressor provides high pressure gas to the cryocooler through a flexible gas line. The expansion of the gas at different stages produces the refrigeration. Low pressure gas is then returned through another gas line where it is recycled through the compressor. This closed loop cycle can be continuously repeated and maintained as needed to produce the desired refrigeration. The DE202G cryostats on XMaS is designed to mount directly onto the phi circle of the Huber diffractometer and can be oriented in any direction at base temperature. Currently there are two of these cryostats on the beamline, one with silicon diode temperature sensors and the second has a cernox sensor installed for use in magnetic fields.

Both the vacuum shroud and radiation shield are equipped with beryllium domes for x-ray studies allowing full access to the sample. The shroud is constructed from non-magnetic stainless steel which slips over a double o-ring on the refrigerator for easy sample change. The radiation shield is constructed from nickel plated copper for effective heat transfer. The distance from the tip of the cold finger to the centre of rotation is 17.5 mm.

8 K - 800 K ARS DE202G Cryofurnace

This cryofurnace is based on the ARS DE202G. The 800 K Interface mounts on the cooler and contains an internal mechanical thermal switch which protects the cold end from excessive heat while experiments are carried out at elevated temperatures. A heater and thermocouple sensors provide a temperature range from 8 K to 800 K.

1.7 K - 300 K He 4 ILL Joule Thomson Cryostat

In addition to a commercial standard two stage displex cryostat, which operates down to ~10 K and mounts on the phi circle of the diffractometer, a specially adapted 3 stage displex capable of sample temperatures down to 1.7 K is in routine use. This novel device, which has been developed by the cryogenics Laboratory at Institut Laue Langevin, Grenoble, may be operated over a wide range of angles without degradation of base temperature. The three stage device is ~40 mm longer than a standard displex, but is installed into the same motorised phi circle mount as all of the other cryostats.

1 K - 300 K He 3 ILL Joule Thomson Cryostat

Using the above Joule Thomson cryostat with ³He gas, instead of ⁴He test experiments have been made with sample temperatures of 1 K.

Cryogenic Sample Holders

The distance from the end of the APD cryostat "cold finger" to the centre of rotation is 17.5 mm. Samples are usually mounted onto a 6 mm diameter copper stub, that can then be mounted into a standard sample holder. For larger or unusually shaped samples, mounts can be made on request. Please contact the beamline staff to discuss your requirements before arriving for the experiment.

Temperature Controllers

The standard temperature controller used on the beamline is the Lakeshore model 340. This controller supports a very wide range of temperature sensors and has four inputs. Further details of this controller can be found on the Lakeshore website.

http://www.lakeshore.com/temp/cn/340po.html

Magnetic Fields

Currently there are two large magnets which can be mounted within the Huber diffractometer.

1 Tesla Electromagnet

The 1 Tesla electromagnet magnet at the XMaS beamline, supported from the base of the Huber diffractometer, fits within the Eulerian cradle as shown below. The geometry allows the magnet to be oriented in one of three positions 90° apart, about the vertical axis. Thus both transverse and longitudinal fields may be applied, allowing the separation of spin and orbital contributions to magnetic scattering signals. Also the magnet may be rotated to allow the application of a vertical field in a horizontal scattering geometry. The geometry of the yoke allows for the maximum number of field turns within the geometrical constraints of the diffractometer. It can deliver a field of 1.0 T in an air gap of 50 mm. To achieve this with a magnet of manageable size, water cooled hollow conductors have been used for the coils. A magnetically efficient yoke configuration occupies the lower half of the vertical scattering plane, leaving the other half open for the cryostat and scattered beam. The yoke and poles have been manufactured from ARMCO grade iron. The gap set at 50 mm, the homogeneity of the field in the middle of the gap in a co-axial cylinder, a = 5 mm, r = 2.5 mm is within 2% of the central value. Conical pole tips can be mounted on the adjustable poles and, with a 25 mm gap, a field of 1.5 T is achievable at a current of 250 amps.

	B horizontal and along the incident beam	B horizontal and perpendicular to the incident beam	B vertical and perpendicular to incident beam

Specifications ( 50 mm Gap )

4 Tesla Superconducting Magnet

The XMaS/AMI superconducting magnet has been designed to fit within the Euler cradle of the Huber diffractometer and allows three field orientations. The geometry allows the magnet to be turned along the vertical axis through 90º, facilitating application of magnetic fields both along and transverse to the incident beam direction. Thus, both transverse and longitudinal fields may be applied. This allows the separation of spin and orbital contributions to magnetic scattering signal in non-resonant ferromagnetic studies [3,4,5]. It may also be mounted to provide a vertical field allowing additional contrast in resonant magnetic scattering studies. It can deliver a field of 4 T in a large 40 mm opening warm bore with a 180º scattering aperture. An efficient yoke configuration occupies the lower half of the vertical scattering plane, leaving the other half open for the cryostat and scattered beam. The geometry of the coil former has been optimized to allow for a maximum number of turns within the geometrical constraints of the diffractometer. The combination of the new 4 Tesla magnet and low temperature insert at XMaS will also enable detailed studies of complex field and low temperature (~2 Kelvin) phase diagrams. The 180º scattering aperture allows large access to reciprocal space, so that important information on wave-vector dependence can be readily obtained. As this magnet can be used in vertical or horizontal scattering geometry, which will allow the experimentalist to take advantage of either incident s-polarised or p-polarised photons from the ESRF storage ring.

The primary design requirements for this magnet were that it should be able to operate in any angular geometry, thus necessitating a cryogen free design. It was also decided that the magnet should be able to fit within the Euler cradle of the Huber diffractometer. Another important criterion for the design was a 180° open warm bore access for the scattered x-ray beam, allowing access to a very large area of reciprocal space. The three versatile geometries of operation of the magnet mounted within the Huber diffractometer are shown below:

The superconducting magnet, shown below, is wound of twisted multifilamentary Niobium-Titanium (NbTi) superconductor embedded in a copper matrix. Twisted filaments maximize magnetic stability and minimize magnetic hysteresis. The former for the magnet coil is constructed of non-magnetic titanium alloy. Quench protection diodes are mounted within the magnet. The magnet system has been optimized to allow for a maximum number of ampere-turns within the geometrical constraints of the diffractometer. One of the most demanding requirements was the provision for 180° of clear room temperature radial access to the 4 Tesla central magnetic field, while maintaining a fixed, compact outer vacuum vessel which fits within the various Huber diffractometer configurations. At 4 Tesla, the split coil magnet produces a force of approximately 68,000 N, which acts to collapse the 180° gap. The magnet former was designed to support these forces and be rigid enough to minimize coil movement, which could cause a premature quench (i.e., below 4 Tesla). The field magnitudes are shown in figure 3, with the plots in the zr plane. The z-axis is along the main axis of the split coil and the r-axis is along the radial axis of the split coil. Although the central field at z=0, r=0 is 4 Tesla, the peak fields within the windings are approximately 8.5 T. This is approaching the critical field limit of about 9 Tesla for the Nb-Ti wire used in this magnet, with some margin for conduction cooling. A commercial Sumitomo closed cycle refrigerator is used to cool the magnet system and AMI high temperature superconducting feedthroughs are installed to energise the magnet, whilst minimizing the heat load on the refrigeration system. The requirement that the refrigerator should be located remotely from the magnet, due to the need for multiple orientations within the Huber diffractometer also caused a number of design concerns. The vacuum vessel of the magnet needed to support the weight of the refrigerator and it was also to ensure a good thermal conduction path between the magnet and the cryocooler. Heat transfer between the magnet and the cryocooler is accomplished by thermal links located within the torque tube (LABEL). Differential thermal contraction is mitigated though flexible joints on both the first and second stage thermal links from the cryocooler. Another problem associated with multiple magnet orientations was locating the cold (< 4 K) magnet assembly within the radiation shield and vacuum vessel. Internal supports made from glass-fibre reinforced resin were designed to support the full weight of the magnet (some 34 Kg) in radial and axial loading conditions, whilst simultaneously limiting the heat loads to the magnet to less than 200 mW. These supports also have to tolerate the dimensional changes due to the thermal contraction of dissimilar materials whilst locating the magnet in its correct position. In some areas there is less than 4mm between the cold magnet and the vacuum vessel at room temperature, as shown in figure 2.

Figure 3: The 3D-magnetic field profile when the system is energized to 4.0 Tesla. Peak fields of ~8.5 Tesla can be seen within the windings at ~±7cm along the z axis.

The variable temperature insert is based around a RICOR 2/9 two-stage displex, capable of reaching 10 K. However, a third stage has been developed by the cryogenics group at the I.L.L. in Grenoble [7]. This novel device is capable of operating down to 1.7 K using 4He gas to within a few mK stability. It may also be operated over a wide range of angles without degradation of the base temperature.

Electric Fields

The classic demonstration that a sample is ferroelectric is to measure a spontaneous polarisation that is switchable by the application of an electric field – namely a P-E hysteresis loop (Figures 1-2). In collaboration with the NPL Functional Materials Group, the XMaS team has developed an in-situ system where P-E loops and x-ray diffraction data are collected simultaneously (Figure 3). This development aims to help users to carry out studies of ferroelectrics and multiferroics in complex conditions such as magnetic and electric fields. Currently XMaS offers an electric field sample environment with potentials of ± 2 kV with temperatures down to 2 K in a 4 T magnetic field. A separate sample environment provides ± 10 kV down to 10 K in a 1 T field. Samples must be coated with e.g. gold and electrically isolated by a sapphire support. The HV wires that are connected to the cryostat, are soldered on the gold (Figure 4).

Figure 1: Polarisation Field (P-E) measurement of poled soft PZT composition taken at 1 Hz, five consecutive loops overlaid.	Figure 2: Polarisation Field (P-E) measurement of a 1 μF ceramic multilayer capacitor taken at 1 Hz. The sample is a composite multiferroic with a sandwich of piezoelectric dielectric with magnetostrictive nickel electrodes.

The electrical response and the diffraction data can be measured simultaneously by means of a fast acquisition card (Figure 3) under the application of either a constant or oscillating field. The MUSST (Multipurpose Unit for Synchronisation Sequencing and Triggering) card developed by the ESRF can collect data in each separate channel at rates up to 20 MHz.

Figure 3: Schematic of in-situ PE loop measurement system used at XMaS.	Figure 4: Sample gold coated on two sides and mounted on a sapphire plate for electric isolation. The two HV wires soldered on the gold are connected to the cryostat.

More information can be found on the Multiferroics wiki development by NPL.  http://interactive.npl.co.uk/multiferroics/index.php/Instrumentation

For more details on the P-E measurement system contact Mark Stewart at NPL, e-mail:   mark.stewart@npl.co.uk

Custom Sample Environments at XMaS

If any custom sample environments are required, please contact a member of beamline staff as soon as possible and we will try to accomodate you. Previous examples have included equipment for performing in-situ studies of surfaces in the electrochemical environment. Electrochemical cells have been developed to allow control of the solution and sample temperature over the region of -5C to 80C and to permit studies of electrochemistry in a magnetic field. Preliminary experiments on the surface reconstructions of Au(111) and Au(001) in electrolyte have been performed.