Date : 9/8/2018 6:29:24 PM
From : "asafp"
To : "Aczel, Adam A." , "eladc"
Cc : "Huq, Ashfia"
Subject : Re: magnetism in MAX phases: a pre-proposal contact


Dear Ashfia and Adam,

Thank you for your comments and review.

As El'ad wrote, we will revise accordingly and submit.

Regards,

Asaf

From: Aczel, Adam A. <aczelaa@ornl.gov>
Sent: Friday, September 7, 2018 4:50:21 PM
To: eladc; asafp
Cc: Huq, Ashfia
Subject: RE: magnetism in MAX phases: a pre-proposal contact
 

Hi El’ad and Asaf:

I have reviewed your proposal and made some changes to the HB-1A portion. The science case is strong and this is an appropriate experiment for the instrument. Ashfia’s recommended changes for POWGEN will need to be incorporated in my modified proposal attached here before you submit it to IPTS.

 

Regards,

Adam

 

From: eladc <eladc@iaec.gov.il>
Sent: Thursday, September 06, 2018 10:20 PM
To: Huq, Ashfia <huqa@ornl.gov>; asafp <asafp@nrcn.gov.il>
Cc: Aczel, Adam A. <aczelaa@ornl.gov>
Subject: Re: magnetism in MAX phases: a pre-proposal contact

 

Ashfia,

Of course it helps!

When Asaf is back to Israel I'll discuss all details with him and we'll send the proposal ASAP.

Is the mail-in option RT only?

El'ad

From: Huq, Ashfia <huqa@ornl.gov>
Sent: Friday, September 7, 2018 1:11:46 AM
To: asafp; eladc
Cc: Aczel, Adam A.
Subject: RE: magnetism in MAX phases: a pre-proposal contact

 

Asaf and Elad

 

The temperature range you are after is a bit tricky.  The cryofurnace allows you to go past 300K but not below 5K.  However, it takes ~5 hours to get down to base temperature at POWGEN.  So measuring a large number of samples will be time intensive.  The data collection time for Rietveld is not too long but since all of this is manual you can at best do 2 samples/day with multiple temperature points.

 

If however, you use the sample changer you can only go 10-300K.  I spoke to Asaf and perhaps one possibility is to do a few samples as mail in to figure out the data quality.  We can also use the changer to measure everything below 300K if 10K is good enough for your low temp and that can be done pretty fast and only ask for the cryofurnace for 300K and above, then we won’t have to wait 5 hours every time to get to base.  It takes 40min to get to 10K in the changer and we can change samples at 10K

 

For the proposal itself, the figures are not very clear.  It will be important to see the expected phase transitions clearly from your transport measurement so I would make the graphs larger and even zoom into temperatures of interest so that the reviewers don’t think it is a “fishing expedition”. 

 

At powgen the lowest temperature we can get to is 2K with the Orange Cryostat but that is also limited to 300K. 

 

I hope this helps

 

Ashfia Huq
Instrument Scientist POWGEN

Spallation Neutron Source
P.O. Box 2008, MS 6475
Oak Ridge, TN 37831


Please do not send samples to above address.  For shipping information and other instrument related information go to our website.

http://neutrons.ornl.gov/powgen/users/

 

From: asafp <asafp@nrcn.gov.il>
Sent: Wednesday, August 29, 2018 2:07 AM
To: Aczel, Adam A. <aczelaa@ornl.gov>; Huq, Ashfia <huqa@ornl.gov>
Cc: eladc <eladc@iaec.gov.il>
Subject: Re: magnetism in MAX phases: a pre-proposal contact

 

Dear Ashfia and Adam,

Attached is a draft of the proposal.

I remind you that next week I will be at SNS for an experiment. I will try to contact you when I'm there, if its okay.

All the best,

Asaf

 

From: Aczel, Adam A. <aczelaa@ornl.gov>
Sent: Thursday, August 23, 2018 3:33 PM
To: asafp; eladc
Cc: Huq, Ashfia
Subject: RE: magnetism in MAX phases: a pre-proposal contact

 

OK, sounds good Asaf.

 

Thanks,

Adam

 

From: asafp <asafp@nrcn.gov.il>
Sent: Thursday, August 23, 2018 6:57 AM
To: Aczel, Adam A. <aczelaa@ornl.gov>; eladc <eladc@iaec.gov.il>; Huq, Ashfia <huqa@ornl.gov>
Subject: Re: magnetism in MAX phases: a pre-proposal contact

 

Hi All,

Thanks for the information, it is very helpful. My quick calculation yields ~4 days experiment in HB-1A. If we could, in parallel, bring samples for measurement at POWGEN, that will be perfect. I will write down the experiment plan, and send you soon.

Regards, 

Asaf

From: Aczel, Adam A. <aczelaa@ornl.gov>
Sent: Wednesday, August 22, 2018 4:48:25 PM
To: eladc; asafp
Cc: Huq, Ashfia
Subject: RE: magnetism in MAX phases: a pre-proposal contact

 

Hi El’ad:

Yes, you are correct about the HB-1A configuration and possible counting times. We may be able to get away with 1 min/pt, but we won’t know until the experiment begins. The wavelength at HB-1A is 2.37 A.

 

Regards,

Adam

 

From: eladc <eladc@iaec.gov.il>
Sent: Wednesday, August 22, 2018 12:30 AM
To: Aczel, Adam A. <aczelaa@ornl.gov>; asafp <asafp@nrcn.gov.il>
Cc: Huq, Ashfia <huqa@ornl.gov>
Subject: Re: magnetism in MAX phases: a pre-proposal contact

 

Hi all,

Adam, thanks for this idea, it sounds very good.

I would like to verify that I understand the HB-1A configuration. Is it a single detector 3-axis diffractometer? So, when you say that a point will take 2 min and that 0.2 deg is the usual step size, does that mean that it'll take ~10 min per 1 deg, and 1000 min per 100 deg? Also, from the monochromator type, I assume the wavelength to be ~2.45A. Is that right?

Thank you,

El'ad.

From: Aczel, Adam A. <aczelaa@ornl.gov>
Sent: Tuesday, August 21, 2018 11:12:26 PM
To: asafp; eladc
Cc: Huq, Ashfia
Subject: RE: magnetism in MAX phases: a pre-proposal contact

 

Hi Asaf:

Actually, I just thought of a sample environment we use on HB-1A that would be perfect for you. We have a Janis closed-cycle refrigerator that can easily switch from low T to high T mode. Low T mode operates between 3.5 and 300 K, while high T mode operates from 200 K up to temperatures of at least 500 K. I don’t remember the upper limit for high T mode off-hand, but I can look it up if that becomes important. Switching from one mode to another with a given sample installed is not very difficult. This sample environment is top-loading so sample changes are very quick (~30 minutes). We may even have a three-sample stick available by the time you run your experiment.

 

Regards,

Adam

 

 

From: asafp <asafp@nrcn.gov.il>
Sent: Tuesday, August 21, 2018 3:13 PM
To: Aczel, Adam A. <aczelaa@ornl.gov>; eladc <eladc@iaec.gov.il>
Cc: Huq, Ashfia <huqa@ornl.gov>
Subject: Re: magnetism in MAX phases: a pre-proposal contact

 

Dear Ashfia and Adam,

 

Thanks VERY much for your prompt and detailed response.

 

Reading your answers and considering the experimental constraints you raised, I will aim the experimental plan in the proposal to thorough research on the magnetic structures of the MAX phases. Hence, I will request for a beamtime on HB-1A, which can handle magnetic refinement for our class of material, i.e. with ordered moments < 1 muB. 

Regarding the temperature range - on one hand, our SQUID measurements show merging of the FC and ZFC curves, for all samples, between 300 to 400K - this might be an indication of a phase transition at this temperature range. Moreover, going all the way down 50K, the “interesting” magnetic response seems to appear. Considering these preliminary results, I believe it would be intriguing to measure all nine samples from 50 to 400K, at limited Q-range, to reduce the measurement time.

However, on the other hand, following our published results on (Cr,Mn)2GeC sample showing long range order at 1.5 K, we expect to observe long range order at (Cr,Mn)2GaC and (Cr,Mn)2AlC samples with high Mg-content as well, at the low temperature range, i.e., below 10K. Therefore, in addition to the measurements at T > 50K, we would like to perform on 2 out of the 9 samples (those with the highest Mn content), another set of measurements at T < 10K. I have learned from your answers that these two temperature ranges require different cooling equipment. Considering this, do you think it would be feasible in a reasonable time to start the experiment with the high-temperature closed cycle refrigerator, measure 9 samples and than replace it with a low temperature cryostat and measure two more samples?  

 

Best regards,

Asaf

 

From: Aczel, Adam A. <aczelaa@ornl.gov>
Sent: Monday, August 20, 2018 5:33:40 PM
To: asafp; eladc
Cc: Huq, Ashfia
Subject: RE: magnetism in MAX phases: a pre-proposal contact

 

Hi Asaf:

I followed the same style as Ashfia, so my answers are also in red:

1. Sample environment: what is highest temperature available for measurement at HB-1A?

You can reach 1770 K with a furnace on HB-1A or HB-2A, but we have to be confident that your sample will remain intact if you go that high. We also have high-temperature closed cycle refrigerators for both instruments with a temperature range of 20 – 700 K. Finally, our standard closed cycle refrigerators can be operated between 4 – 350 K.

2. We wish to have a temperature scan. What is the typical stabilization time for a single point, and how long will it take to cool down to the base temperature?

The answer to the first part of this question depends on the temperature step size in your scans. The answer to the second part of this question depends on the sample environment that you plan to use. A standard closed cycle refrigerator cools down from room T to 4 K in about an hour. It may take several hours to reach the first temperature that you desire in the high temperature closed cycle refrigerator or our furnace.

3. Once the temperature was stabilized, what is the typical measurement duration for “good statistics”?

Ashfia’s answer covers the basics. If you are trying to identify a small magnetic Bragg peak at HB-1A, you will probably be counting 2 minutes per point. A typical stepsize in 2-theta is 0.2 degrees. Counting times on HB-2A may be similar but your stepsize in 2-theta will likely be 0.05 degrees due to the increased Q-resolution of that instrument.

4. What are the main disadvantages of HB-2A/HB-1A compared to POWGEN?

I modified your question a little bit, as there are three different instruments that you should consider for your measurement: POWGEN, HB-2A, and HB-1A. Again, Ashfia already covered many of the essential details. I will break things down in this way: POWGEN is best for structural refinements, both HB-2A and POWGEN can handle magnetic refinements equally well in the T-range 10 – 300 K for materials with ordered moments over 1 muB, HB-2A is best for magnetic refinements in the T-range 70 mK – 10 K with ordered moments over 1 muB, and HB-1A is best for magnetic structure determination in the T-range 70 mK – 10 K with ordered moments less than 1 muB. HB-2A and HB-1A can also handle pressure cells and magnetic fields if required.

I would be happy to meet with you in person during your upcoming ORNL visit to chat about your POWGEN/HB-2A/HB-1A proposal in detail.

Regards,

Adam

From: asafp <asafp@nrcn.gov.il>
Sent: Thursday, August 16, 2018 4:21 PM
To: Aczel, Adam A. <aczelaa@ornl.gov>; Huq, Ashfia <huqa@ornl.gov>
Cc: eladc <eladc@iaec.gov.il>
Subject: magnetism in MAX phases: a pre-proposal contact

 

Dear Ashfia and Adam,

 

My name is Asaf, and I am working with El’ad Caspi on magnetism in MAX phases in the Neutron Scattering group at NRCN. A few months ago El’ad emailed you regarding our intention to apply for beamtime at your beamline. I would like to remind you that, we are interested in characterization of crystallographic and magnetic structures of MAX phases, particularly the (Cr(1-x),Mn(x))2AC, A=Al/Ge/Ga family, that showed indication of magnetization. Generally speaking, magnetization in MAX phases is quite rare experimental observation, and usually the magnetic signals are very weak (we have measured a magnetic moment of ~0.5 uB). Following your advice to El’ad, I am preparing a proposal for both POWGEN and HB-1A, tailoring the advantages of these two facilities for the challenging magnetic and structural neutron powder diffraction of the MAX phases. In order to plan the experiment, there are few details that I wish to confirm with you:

 

Finally, I have a beamtime in SNS in the first week of September. I will be more than happy to visit your lab and meet you. I believe that the proposal will be ready by then, and so we will be able to discuss and go over it before submission.

 

All the best,

Asaf