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--- ppms [2006/01/09 14:38] – (old revision restored) 127.0.0.1
+++ ppms [2007/07/04 09:55] (current) – hendrikx
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+**PPMS**  version feb 2007
+===== Resistivity Measurements =====
+Before placing any puck inside the chamber, check the contact resistance:
+A - Plug the puck with the samples mounted into the testing station and insert the resistivity plug into the testing station.
+B - In the computer, using MultiVU software, option Instrument/Bridge Channels, check for the channels you will be using in the measurement. The current limit may be changed, but try to set as default values 100 ma, 1000 mV, 100mV, Drive mode AC and press Set. The value of the contact resistance will appear on the right side of the screen. It should be in the order of a couple of ohms, if you get something in the order of the mega-ohm, check which contacts are the origin of the problem with the multimeter and solve the problem under the microscope.
+C - Remember to plug the resistivity plug back into the system, that the 'grey-Iemo' cable is connected,
+otherwise you will wonder why you are not collecting data and have no clue about it. It should look like this.
+Before inserting the puck inside the chamber, first check the following:
+Is the Temperature of the chamber above 295K? If not, there will be cryopumping of air into the chamber and we do not want that to happen do we? Set the Temperature for 300K.
+Is the field below 1 T ? If you place the insertion tool with a high magnetic field inside there will be a strong force on the insertion tool that may actually overwhelm you and damage the pins while you are inserting the pucks. Set the magnetic field for 1T or less.
+So Check that T=300 K, field = 0 Oe, If not:
+a) go to __Instrument__- __Temperature__ -__Set__: 300 K (fast settle).
+b) go to __Instrument__- __Field-Set__ -linear ( if  field <  0.5 T), --oscillate ( if field > 0.5 T).
+Now you are ready to insert the puck in the chamber. You will be careful in this operation not to bend the pins !!!!
+Disengage the Sample Insertion Tool. The top part should be vertical.  Insert the puck in the bottom part of the sample insertion tool. Remember that the sample faces upwards and the holes of the puck should be on the outside. Rotate the puck slightly to check that it is correctly positioned (If it is stuck, try again before placing the sample installer inside the PPMS or you will damage the pins when you do it !). Now you can engage the sample insertion tool by flipping the black switch down. Check if the puck is well levelled with the cylinder of the sample insertion tool.
+In the Computer, use the MULTIVU Software, option Sample/Install. This will initiate the venting of the chamber.
+Open the clamp, remove the baffles and place the sample installer inside the chamber. Start inserting the sample insertion tool carefully. don 't forget the o-ring.
+Pay attention to the position of the key part of the puck (small metal part). If it was rightwards, you should rotate it left once inside, if it was left, you should rotate right. DO NOT FORCE IMMEDIATELY !!! When you have reached the correct position you will feel a slight depression. Press the Sample Installer Tool to plug the puck into the pins. The tab top part of the sample installer will slightly pop. Disengage the sample insertion tool (Remember: black tab in the up position) and remove the sample installer. Do it slowly, specially at the beginning. If you feel resistance, you might not have inserted the puck well and it might have gotten caught in the tool, so remove the puck and insert again.
+Now put the baffles back inside again and close the clamp. In the MULTIVU Software, you will notice that the Sample/Install option is still open so, click Finished. This will engage the purge/vacuum operation.
+Okay, the puck is finally inside. What shall I do next?
+Check for the contact resistance once more by using the MultiVU software, option Instrument/Bridge Channels, the values should be close to or slightly higher than those checked before. If you cannot read the values, some contact may have been broken while you were carrying out the insertion process. Remove and check your contacts again with the multimeter, repair them under the microscope.
+How do I get the measurement running?
+You will actually have to tell the PPMS6000 how to do it. This means writing a sequence
+Writing a sequence for resistvity measurements, in the MULTIVU program go to
+__New Sequence File__  \\
+Save sequence file with __File__  and __Save As__ \\
+\\
+Set your parameters:\\
+Scan Temperature at the desired rate\\
+Uniform spacing or increments, 1/T or log T\\
+Number of steps (as a function of the other variables)\\
+Sweep (for routine measurements)\\
+In the Measurement Commands/Log PPMS Data/General write the date file name of the sample you will be measuring.
+Options Start, Create New File/Version, Repeat every 5s (for example).
+Option Log PPMS Data/Standard Items, check for Temperature, Field, and the Bridges + Excitation you are using. (You can skip the diagnostic option but if you want you can check the systeml Status, Set point, Magnet and Flow Rate options.
+After End Scan:
+Go to Measurement Commands/Log PPMS Data/General again and check the Stop logging action (instead of start). This will allow you to stop collecting data points at your final temperature. If you don't you will either be collecting a huge amount of points at your final scanning temperature or at 300K (because you will be kind enough to set this to end your measurement J).
+Set Temperature 300K, 10K/m (this is the maximum rate, so even if you put 100 it will still be 10 anyway), in fast settle mode.
+If working overnight or on weekends and no on will follow immediately to do the next measurement, set the final Temperature to 100K to save some Helium. Or insert the Shutdown mode instead (it will keep the flow control valve at a rate of 100cc/m throught the cooling annulus and the systeml heaters are turned off. The impedance heater is also kept at low power to avoid liquid helium to reach the cooling annulus).
+NOTES:
+There are obviously other options you may check in the sequence file editor like the Scan Field, etc., if you will be doing measurements under magnetic field. Or for very precise measurements (you will get good data with the previously mentioned options, but if you want to be really picky, picky, you may wish to use the wait option. This means that the program will wait until the variables you have selected are stable enough in order to proceed with the measurement. It will take you much more time, so do routine data collection!). If you really need to do this, please write several sequences associated to several data files for your own protection. Like from 300 to 200, then scan closely from 200 to 100, then go for a normal rate from 100 to 5K, etc., as a mere example of course !). Also, if using fields higher than 2T (20000 Oe) please set the decreasing field rate for oscillating mode in order to restrain the remnant field to a maximum of 5 Oe).
+Things to remember when writing a sequence for Resistivity in PPMS:(Federica Galli)
+a) Always measure in Hi-Res AC if measuring in mOhm range
+b) When you don 't measure on a certain channel set channel to off
+c) When you measure use 'no overshoot' for field and temp scanning or setting.
+d) When you want to reach a setpoint 'fast', choose fast mode.
+e) Always check that you choose a __data file__ before starting a sequence. Be careful: don't overwrite on previous user's datafile.
+When the measurement is finished:
+. Check that T = 300 K, H-= 0 G.
+. Vent continuous1y ( __Instrument__ -__Chamber__ __Vent/Cont__ )
+. When on PPMS-STATUS -__Flooding__ -Open chamber, take out sample -Close chamber -__Purge/Seal__ !
+===== AC succeptibility/DC magnetization measurements: =====
+ACMS Setup
+In order to set up the ACMS you will need to plug the ACMS Insert into the system. Please follow these procedures carefully due to the sensible nature of the coil set.
+A - In the Control Panel of the PPMS 6000, select the Continuous Venting Mode.\\
+B - Be sure that there are NO resistivity plugs inside the chamber.\\
+C - In the top part of the ACMS Insert, tighten the screw until it blocks.\\
+D - Place that assembly inside the chamber remembering the way you have put the resistivity plug inside. You should press when you fill you have reached the correct position (you will feel the same depression). \\
+E - Remove the screw and be careful not to drop it inside the chamber. It should look like this inside. \\
+F - Place the Sample Transport Assembly of the ACMS and plug the pre-amplifier at the back.
+ACMS DC Analysis Centering Techniques: Linear vs.
+Nonlinear Mode
+When using the DC extraction method in the ACMS option, one is given a choice of two techniques for tracking the sample center: linear and nonlinear. When making immediate mode
+measurements, the user must refer to the dialog on the “Configure” tab of the ACMS control
+center, while when measuring within a sequence this dialog appears in the “Measure” tab of the
+sequence command.
+Before making measurements, the user must center the sample using the “Locate Sample”
+command. In the ACMS measurement .DAT file, the value “Sample Center(cm)” reflects the
+sample location that was obtained during the last sample centering operation. The scale for this
+variable is in motor coordinates, with a value of zero corresponding roughly to an ideal location
+of the sample.
+In contrast to the Sample Center, the “DC Position(cm)” of the sample is determined for each
+measurement individually. The sample DC Position is found either by using a simple linear
+Taylor expansion of the extraction data (Linear Mode) or by iteratively shifting the fitting
+function with respect to the extraction data to obtain the best fit (Nonlinear Mode). These modes
+are akin to Linear and Iterative regression methods (respectively) used in the MPMS software.
+If the DC Position of the sample changes significantly, the linear mode will be less accurate due
+to the limitations of the approximations used in the analysis (see discussion below). Also, the
+nonlinear mode will generally be more accurate because it can adjust the center position and get
+the best fit to the data. However, due to the relative simplicity of the linear mode versus the
+nonlinear mode which can find “false” minima when fitting noisy data, we recommend using
+linear mode for small signals (m < 10-3 emu).
+Based on this, some basic guidelines for making DC extraction measurements in the ACMS are:
+) When possible, measure each data point using both linear and nonlinear modes. When
+analyzing the data it will often be evident which mode is better, based on the reported “M
+Std. Dev.” values and the guidelines below.
+) Take multiple measurements (at least 3) at each temperature and field so that better
+statistics are obtained, as “M Std. Dev.” is sometimes not representative of the real scatter
+in the data. Also, drifts in the data will become evident if multiple data points are taken.
+) For large signals (m > 10-3 emu), nonlinear mode is best.
+) For small signals, linear mode is required.
+) If measuring moment vs. temperature over any significant range, nonlinear mode is
+required as the fitting function must be able to shift to truly fit the data instead of just
+approximating the moment as linear mode does. An alternative to using nonlinear mode
+is to center the sample (“Locate Sample”) frequently as a function of temperature (e.g.,
+every 10 K) and to continue to use linear mode.
+===== Specific heat =====
+Multivu program application.
+I. Check that 'probe' cable is connected.
+. Check that the little cable parallel to 'probe', which is the thermometer cable, is connected to P2 at the back of the bridge.
+. Check that T=300 K, field = 0 Oe, if not:
+a) go to __Instrument__ -__Temperature__ -__Set__: 300 K (fast settle).
+b) go to __Instrument__ -__Field__. __Set__ -linear ( if field < 0.5 T), --oscillate ( if field > 0.5 T).
+. Open PPMS multivu and go to __Utilities__ -__Activate opt__ions -__Heat Capacity__ -__Installation Wizard__  __Prepare Addenda Measurement__ then you can open a __New File__ and edit the optional field, the Header Information comes on top of the graph of the data file
+. Open ( O-ring) chamber.
+. Take out baffle-assembly.
+. Take out previous person's sample! 1
+. Insert your sample-puck, note the number of the puck, insert the dry baffle + charcoal and close chamber: don't forget the o-ring and go on with Purge from menu, if necessary change the puck number.
+. Check if everything is OK: ( Heat capacity option- Puck test result1
+. From __Measurement__ tab choose __Create New Addenda Table__ and look for __Suggest__ __Defaults__ and put the values, the optional title wi11 come in the puck.cal file. When you want to split in more temperature ranges, you have to activate a sequence file and add __New Addenda__, this table comes also in the puck addenda table of the selected puck.cal file.
+. Activate the new addenda measurement or the sequence.
+**When the addenda measurement is finished...**
+. Open __Installation Wizard__ -__Prepare Sample Measurement__- Open Chamber, take out puck, mount sample, put the puck back, insert the dry baffle-assembly, close the chamber and activate __Purge and Next__.
+. Check puck serial number and activate __Next__ and verify the current addenda table, __Open New File__ give the values of the sample, set Sample heat capacity units to J/mole-K and __Finish__.
+. Open __Measure__ and __Measure Sample Heat Capacity vs Temperature__... and give the values, when you want to split in more temperature ranges, you have to activate a sequence file and add __Sample HC__ and give the values and end with setting the field to 0 Tesla and the temperature to 300 K.
+Things to check when running Cp-measurements
+On the 'Measurements Status Viewer ":
+a) Sample Coupling: it should be between 95-99 %
+b) It should not take too long time (drift rate steps should not be too many: around 5 or 10 ), else the temperature __Settling Accuracy__ is too small in the __Heat Capacity vs Temperature menu.__
+====== Troubleshooting ======
+Ice in sample chamber: you may notice this when cooling down becomes very slow and lowest temperatures cannot be reached.
+This ice forming can be due to two things: leaking of the O-ring at the top of the sample chamber or a leaking relief valve at the backside of the sample chamber.
+To remove the ice you should \\
+) set temperature to 300K \\
+) remove your sample \\
+) open the sample chamber to air and increase the chamber temperature to 400 Kelvin until the ice is gone while venting continuously (with helium)\\
+Because the pump pumps relatively large volumes of Helium, the rotary pumps loose oil to the outlet. Once every few weeks, check the oil level in the drain and remove the oil.
+For serious problems: contact  Stefan Riesner/ Thamas Beppler at Lot-Oriel, Darmstadt, Germany. \\
+Stefan Riesner \\
+Phone +49 6151 880667 \\
+Fax: +49 6151 896667 \\
+E-mail: riesner@lot-oriel.de \\
+Thomas Beppler \\
+Phone +49 6151 8806573 \\
+Fax: +49 6151 896667 \\
+E-mail: beppler@lot-oriel.de  \\
+===== Calibration/Configuration files =====
+* MPMS_XL \\
+ {{data:calibr_ppms.zip}}