Strain-Magnetooptics in Single Crystals of CoFe₂O₄

Round 1

Reviewer 1 Report

My comments are given in the attached file.

Comments for author File: Comments.docx

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

  I have reviewed the paper focused on studying the magneto elastic and magnetoptic effects in a CoFeO material system.  The work is detailed and explanations are provided.  However, this reviewer has several questions concerning the work that should be addressed in the manuscript to clear up any confusions.  Also this reviewer believes this is excellent work but this reviewer also believes that better descriptions for the cause and effect of magnetoelastic on optical properties is warranted.  See below for comments.

1.  Page 2- authors indicate samples were ground/polished to grain size decreased to 0.5microns.  This statement is confusing because authors indicate this is single crystal.  Please clarify in manuscript.

2.  Page 2 - roughness is 1 micron, this appears "very rough" could authors provide an additional one sentence commentary also what thickness were cut and measured?

3.  page 4- did authors use strain gauges they state use of "tensometric" method which this reviewer is unfamiliar with. Also was the strain measured along one axis and the field applied along two different axis or was the strain measured along two axis and field applied along one axis.  Please clarify. 

4. Section magnetization- authors attribute the jump in magnetization data for fields applied along 110 direction to magnetostriction (fig 2).  This reviewer believes authors are observing the magnetization of individual domains jump from one easy axis (100) to another easy axis that is closest to 110 and this is what causes the multiple steps.  What the authors may find is at larger fields there is a slow rotation from the nearest 100 easy axis to the final 110 direction the magnetic field is applied along.  Please modify the paper to reflect this or provide more concrete explanation of stress causing this intermediate jump.

4.  Figure 3 - was the field applied along a single direction and the strain measured along two different directions.  A better explanation of this test is needed. 

5.  This reviewer is confused by the assessment of magentostriction coefficients to the magnetic crystalline anisotropy MCA.  Usually, magnetostricion is desired in soft ferri(o)magnetic materials.  That is, the MCA represents a barrier over which one much mechanically rotate the magnetic spins.  Thus, for terenol-D the energy present in the magnetostriction contribution is very larger because MCA is relatively small.  Since CoFeO has a moderate MCA it does not seem suprising that the magnestorciton contribution is reasonable. One last quick comment here, is from a fundamental perspective, the magnetostriction terms is the second order expansion of the MCA, i.e. the term that adds anisotropy due to distortion of the crystal lattice.  The point this reviewer is trying to make is I am not sure why the authors are discussing this in the context of this paper and hopefully if this topic is important my comments could help that narrative in the paper.

6.  Page 11, authors state that they can suggest higher values of index of refraction are attribute to pronounced magnetoelasic properties.  I do not see any information that provides strong evidence of this on the figures up to this point.  I do note that they authors have plots for different magnetic fields, but this reviewer would believe that rather than attributed to the magnetoealsetic effect these are probably attributed to the orientation of the magnetic spins along different axis as related to the measurement direction.  Authors may want to argue that this orientation can be also caused by a magneto elastic effect but this reviewer does not see the direct correlation between magneto elastic and the index of refraction authors are suggesting. 

 

7. Figure 8 - Authors compare this to Figure 3 for comparison purposes.  However, this reviewer believes that Figure 3 plotting strain versus magnetic field illustrates that the magnetic spins/domains are changing with the applied magnetic field.  Thus, as the sample strains the local spin orientation changes and this change leads to the changes listed in Figure 8.  This reviewer believes that the reported changes are due to magnetic orientation which is also strongly influenced by the magneto elastic field, but it is the spin reorientation causing the changes in Figure 8.  Thus this reviewer believes the change is caused by spin reorientation WHICH is influenced by magneto elastic.  Can authors please comment on this topic in the manuscript. 

Author Response

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Author Response File: Author Response.pdf