Influence of Concentration Fluctuations on Relaxation Processes in Spin Glasses

Round 1

Reviewer 1 Report

Combining atom probe tomography and neutron spin echo (NSE), the authors 

investigate the influence of clusters of ordered spins on the freezing of   

spin fluctuations to a spin-glass ground-state. 

The conclusion of the article is that 

NSE data can be interpreted in a similar way as in diluted spin-glasses. 

Apart from a few minor comments that should be considered, I think that 

the manuscript should be accepted for publication. 

1.- To my opinion the first sentence of the manuscript is misleading. A spin-glass ground-state 

forms because of frustrated interactions and disorder and not the contrary.

2.- I would add a reference at line 99 for the IVAS software if there is one.

3.- The authors show the NSE data in Fig. 3 that they explicitly reproduce in table 1. 

I am not sure this is necessary but if they decide to do so, the authors should check that 

there are no typos in the entries. For ex., at T=34.2K around NSE time 0.05 ns, I think 

the data in the table does not correspond to the Figure?  

4.- Finally, it is concluded that the ground-state consists of magnetically 

ordered islands embedded in a spin-glass state. I think the authors should comment 

on two additional points:

  1.- if neutron diffuse scattering would be able to observe islands of size 200 ang. 

  2.- if a local probe like \muSR would bring additional information about the freezing 

      of spin dynamics in cluster-type spin-glasses.

Author Response

1.- To my opinion the first sentence of the manuscript is misleading. A spin-glass ground-state forms because of frustrated interactions and disorder and not the contrary.

Reply:

The referee is correct. We have reworded the first sentence in the manuscript as follows: Spin glasses possess no long-range magnetic order due to frustrated magnetic interactions and disorder, which leads to stochastically oriented magnetic moments.

----------------------------------------------------------------------------------------------------------------------------------------2.- I would add a reference at line 99 for the IVAS software  if there is one.

Reply:

We have added a reference to the software package IVAS (Ref. [15].

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----------------------------------------------------------------------------------------------------------------------------------------3.- The authors show the NSE data in Fig. 3 that they explicitly reproduce in table 1. I am not sure this is necessary but if they decide to do so, the authors should check that there are no typos in the entries. For ex., at T=34.2K around NSE time 0.05 ns, the data in the table does not correspond to the Figure?

Reply:

The referee is right, Table 1 may not be clear and be even misleading. The table contains data from the beamline RESEDA (the first approximately 18 lines) and JNSE (the last approximately 10 lines). The data overlaps in time. Therefore, the spin echo time does not increase monotonically. In order to distinguish the two data sets we have chosen to show the JNSE data with slanted characters. In addition, we have expanded the table caption.

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----------------------------------------------------------------------------------------------------------------------------------------4.- Finally, it is concluded that the ground-state consists of magnetically ordered islands embedded in a spin-glass state. I think the authors should comment on two additional points:

1.- if neutron diffuse scattering would be able to observe islands of size 200 ang.

 2.- if a local probe like \muSR would bring additional information about the freezing of spin dynamics in cluster-type spin-glasses.

Reply:

1. Because of the size distribution of the various islands the diffuse scattering data would simply provide a featureless q-dependence. The width of the distribution may change with temperature. However, it seems not be possible to obtain a distribution of domain sizes. This is way we have used APT.

2. We have added in the introduction a reference to the mSR method and the available time scales.

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Reviewer 2 Report

The manuscript is described about the relaxation of spin in Fe_17.8Cr_82.2 observed by neutron spin echo, APT, and ac susceptibility. The nse results clearly capture the relaxation of spin fluctuation in the system on the order of nanoseconds. On the other hand, the interpretation of the observed intermediate scattering functions by the Weron model is leading to the insecure results. In such situation, other complementary experimental results are necessary. For instance, quantitative analyses of the APT results may be helpful to obtain the corresponding static information. SANS results with polarization analysis will be also straightforward for the interpretation of NSE results. 

In case that additional experiments or analyses are difficult, the authors have to show the more concrete reasons of the fixing parameter k = 2.5. This assumption must be very important and should be quantitatively proven in the manuscript.

The corrections and improvements in manuscript are necessary, which are described below.

In page 3

Wrong: 120 * 30 mm^2

Correct: 120 * 30 nm^2

In figure 3, the data sets from RESEDA and JNSE should be separated. The error bars of the data points should be shown. (I suppose that table 1 is not indispensable.)

In figure 4, the fitting qualities should be shown by adding error bars.

Author Response

For instance, quantitative analyses of the APT results may be helpful to obtain the corresponding static information.

Reply:

We do not understand the objection of the referee, because we have analyzed the APT results quantitatively using the software package IVAS as shown in Fig. 2. In addition, we provide the concentration distribution of Fe and Cr. The sum of the contributions sums up to 100% showing the reliability of our analysis. We have added a reference to the used software package IVAS (Ref. [15] and to a publication about the analysis of APT data.

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In case that additional experiments or analyses are difficult, the authors have to show the more concrete reasons of the fixing parameter k = 2.5. This assumption must be very important and should be quantitatively proven in the manuscript.

Reply:

As we explain in the paper, if the Weron model is fitted to our data we obtain unreasonable values for the lifetime of the relaxation process, i.e. t and b do not decrease with decreasing temperature to values below 1. The fits show that k has to be restricted to a value below k = 4 to yield a decrease of t with decreasing temperature. The key message of the results is that the non-divergence of k implies that the number of independent relaxation processes is limited, i.e. spin clusters survive and interact with each other. We have redrawn Fig. 4 and provide error bars for the restricted fits.

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----------------------------------------------------------------------------------------------------------------------------------------Typographical error: Wrong: 120 * 30 mm^2 - Correct: 120 * 30 nm^2.

Reply:

The typographical error is corrected. We thank the referee for pointing out the mistyping.

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In figure 3, the data sets from RESEDA and JNSE should be separated. The error bars of the data points should be shown. (I suppose that table 1 is not indispensable.).

Reply:

It is not reasonable to separate the data as measured with the two spectrometers because the individual data sets would not cover the total range of spin-echo times. In order to distinguish the data of RESEDA from the data of JNSE, we have given the data in Table 1 for RESEDA and JNSE in roman and in slanted letters, respectively. In addition we have modified the caption of Table 1. The time-range for the two spectrometers is already given in the original text. We also quote now the time-range in the caption of Table 1. The error bars are only given in the table and not in Fig. 3 because they would fill up the figure too much.

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In figure 4, the fitting qualities should be shown by adding error bars.

Reply:

We have added the error bars for the parameters obtained by the constrained fits.