Effect of Metal-Oxide Phase on the Magnetic and Magnetocaloric Properties of La0.7Ca0.3MnO3-MO (MO=CuO, CoO, and NiO) Composite
, Sunil Karna 3,* and Sanjay R. Mishra 1,*Round 1
Reviewer 1 Report
The manuscript discusses structural and magnetic properties of oxide-modified magnetocaloric materials based on La0.7Ca0.3MnO3 (LCMO). The authors examined a structure of the perovskites manganite using x-ray diffraction, while magnetic properties were studied using a PPMS magnetometer. In my opinion, the most important results are isothermal magnetization curves and their analysis showing enhancement of relative cooling power. This improvement of magnetocaloric properties is not big, but demonstrates that the doping of LCMO with transition metal oxides is reasonable and opens up new research opportunities. Also noteworthy is a thorough review of the literature on oxide-based magnetocaloric materials in the first part of the paper.
The manuscript concerns a current topic and presents interesting results. I believe the manuscript meets the journal’s standards and scope, however, several issues need to be addressed or discussed before publication:
1. The authors claim that "MO peaks do show an increase in intensity with an increase in their wt.% content in the composite samples." However, it is not clearly visible in Figure 2. Please explain why the intensity of the CuO and CoO peaks is the same (or very similar) regardless of the oxide content in the material.
2. Please compare the crystal lattice constants for the LCMO obtained by the authors with the reference data for the bulk material contained in other publications. Similarly, please compare the obtained lattice constants for oxides with the data for the bulk reported by other authors. Please comment on the differences.
3. Please correct the values of "cell volumes" in table 2. Calculations based on the given lattice parameters give different values than those included in the table. The differences in most cases are not significant, but they exceed the stated measurement uncertainty for some samples.
4. The increase in magnetization for samples doped with 5% CuO is quite reliably explained by the authors. However, it can be expected that for CoO-doped samples we should also deal with the same process, since Co2+ ions should be also expected to substitute the Mn ions. How do the authors explain the gradual decrease in magnetization observed for the samples containing CoO?
5. The authors rightly argue that a good magnetocaloric material should have high thermal conductivity. Please describe how this parameter changes when LCMO is doped with metal oxides.
Minor remarks:
1. The legend in Figure 5 is illegible, especially for Figures f and g. Please correct.
2. Table 6 should be placed in the text immediately after Table 5.
3. Please correct the editorial errors regarding the references to figures.
Author Response
Please see the attachment.
Author Response File: 
Author Response.doc
Reviewer 2 Report
In this manuscript, the authors describe the effect of metal-oxide second phase on the magnetocaloric effect of LCMO-MO composite samples. Although no additional experiments are needed, significant modifications of the manuscript are needed as described below before publication:
1. Page 2: the authors state “RCP of the composites have been predicted to show promising results”. It would be better if some details of the “promising results” can be explained for readability.
2. Please modify the chemical formulas in Figure 1. They should be (NO3) instead of (NO)3. Also, please use subscript properly in the formulas.
3. In Table 2, it seems weird to me that the lattice constants have 3 decimal places while the standard deviation is 0.01 angstrom. Please revise and make them consistent. A Rietveld refinement would give correct error bar.
4. In Table 2, the lattice parameters for LCMO phases are inconsistent when different MO phases present. With larger amount of NiO, the cell volume and lattice parameters of LCMO phase increase. However, opposite trends are observed for CuO and CoO. Please explain in the context.
5. In Table 3, it will make more sense to me if the TC can be presented without decimal place since they are only estimated from the peak positions in the insets of Figure 3.
6. Page 8, the author state “The value of magnetization at low temperature, 5K was observed to decrease with the increase in MO content for LCMO-NiO and LCMO-CoO, while LCMO-CuO showed an increase at 2.5% CuO content”. This is inconsistent with what’s shown in Figure 3. Please revise.
7. In Figure 3, for both MO = NiO and CuO, the magnetization at the lowest temperature for 2.5% of MO is bigger than the pure LCMO sample when the applied field is 1000 Oe. However, in Figure 4, the saturated moments for both cases are consistent with the concentration of the MO phase. Although explanation has been found in the context. But enlarged figures for the range from, say -2000 Oe to 2000 Oe, will be needed to show when the crossing of two hysteresis loops happens.
8. In Figure 5, a brief explanation is needed for the change of slope at around 3 kOe in 5% CuO. What is the origin for the kink? Does larger concentration of CuO induce such meta-magnetic transition?
Author Response
Please see the attachment.
Author Response File: Author Response.doc
Round 2
Reviewer 1 Report
Thank you very much for addressing the questions and comments contained in the review. I believe the manuscript has been sufficiently improved and is ready for publication.
