Peer review of: Large magnetoelectric coupling in multiferroic oxide heterostructures assembled via epitaxial lift- (2020)

Reviewers' comments: 

Reviewer #1 (Remarks to the Author): 

The authors report on the demonstration of tuning the magnetic properties of LSMO thin films using a 
single crystal of piezoelectric PMN-PT. The uniqueness of this study is that the LSMO film is not grown 
epitaxially on the PMN-PT, but grown first on SrRuO3-templated SrTiO3 substrate which is 
subsequently released by selective etching of SrRuO3 and transferred onto PMN-PT. This method 
realizes high quality LSMO thin films with lattice constants close to bulk. The strain state of LSMO was 
successfully manipulated by the applied voltage to the PMN-PT allowing enhancement in bulk 
magnetization as well as controlling the magnetic anisotropy. 

The manuscript is well organized and the benefits of using single crystalline films released from the 
grown substrate is well presented. Overall, I would like to recommend this manuscript to be published. 
However, I would like to request the authors to address the following questions: 
1. Page 5. The authors state, “…confirmed a good match between all three in-plane lattice parameters.” 
What were the actual lattice parameters? It would be more instructive to show in real numbers. 

2. Fig. 1c. Unlike epitaxial LSMO/SRO//STO, in which the substrate 2theta position can be used as the 
reference, how accurate is the 2theta values for the transferred film? The presence of an amorphous 
layer between Pt and the expected built-in strain gradient in the as-grown LSMO make me think that 
the LSMO may not be parallel to the substrate surface. Since the authors discuss the structural 
variation based on XRD with comparison to bulk, characterization of the offset angles along x, y with 
respect to the PMN-PT substrate would be helpful. 

3. I am curious if the as-grown in-plane lattice constants were clamped to the STO substrate or 
slightly relaxed to the SrRuO3 in-plane lattice constants since their saturation magnetization of 2.2 
muB/Mn is still below the ideal value of >~ 3 muB/Mn. 

4. Fig. 2(b-e). It would be instructive if positions of ideal diffraction spots are added together with the 
experimental data. For non-specialists in LSMO or PMN-PT, it would not be easy to capture the relative 
shift with respect to the expected values. 

5. I believe NaIO4, a very strong oxidant, should be capable of oxidizing LSMO, a mixture of Mn3+ 
and Mn4+. The enhancement of saturation magnetization, lattice parameter variation, and partial 
mechanical cracking after release could be partially affected by the (surface) chemical oxidation of 
LSMO during the selective etching. I am curious if the authors can comment on this point in the text. 
Possibly, their XAS or EELS show characteristic features of Mn valence in LSMO. 

Note: The Supplementary documents were not uploaded and therefore my comments are based on 
reading the manuscript only. 



Reviewer #2 (Remarks to the Author): 

Large magnetoelectric coupling in multiferroic oxide heterostructures assembled via epitaxial lift-off 

Pesquera et al. 

The authors present an experimental study of strain mediated electrical control of the magnetization in 
a thin La0.7Sr0.3MnO3 film. 
The film was epitaxially grown on SrRuO3/SrTIO3(100) and transferred, after lift-off, to a 
0.68Pb(Mn1/3Nb2/3)O3-0.32PbTiO3 (PMN-PT) single crystal substrate. 
Application of an electric field to the PMN-PT substrate induces 0.1% strain producing strain in the 
transferred film, enhancing the LSMO magnetization. The magnetic coupling is as strong as in epitaxial 
LSMO and the magnetization is stronger. The results therefore present a way of circumventing the 
epitaxial strain-induced suppression of magnetization and suggest that the lift-off technique may be 
generalizable to other functional perovskite films. 
The main result is therefore of interest and sufficiently innovative to merit publication in Nature 
Communications. However, the manuscript suffers from a number of shortcomings which cast some 
doubts on the generality of the conclusions and which should be addressed. 
The abstract contains the statement that the “strain mediated magnetoelectric coupling is comparable 
with respect to epitaxial heterostructures in which film magnetization is degraded by epitaxial strain”. 
This requires some explanation, at least in the manuscript, because it is difficult to understand for the 
more general reader why in the presence of strong coupling the magnetization is degraded. The use of 
the term “magnetoelectric coupling” is also debatable since in the present case it is the strain which 
changes the magnetization of the LSMO, not the electric field which is only used to induce either 
deformation or phase change in the PMN-PT substrate. I would argue that the authors’ observation is 
in some ways closer to magneto-striction than magneto-electric coupling. 

It is also difficult to understand why in the introduction (page 3) the authors emphasize ferroelectric 
substrates when it is the field-induced strain in the substrate which modifies the LSMO magnetization. 
Presumably, the authors need the ferroelectric switch in PMN-PT to obtain the maximum piezo 
response? If so this should be clearly stated. Strain could, in principle, also be produced by the 
converse piezoelectric effect. Is it necessary to switch the ferroelectric polarization to produce the 
required strain? The authors themselves point out that the strain states are not produced by a 
straightforward ferroelectric switch in the single rhombohedral phase but rather by the reversible 
rhombohedral-orthorhombic phase transition during the switch. 

Two crucial points in the process are not sufficiently underlined and should be of interest to the 
general reader. First, that lift-off and transfer allow getting round the inconveniences of the epitaxial 
constraint, for example, magnetization suppression. Second, transfer allows envisaging in principle 
integration of perovskite films into CMOS compatible technology, hitherto a real obstacle to 
applications. Some more discussion of this perspective would be welcome. 
Figure 1b shows a 8-9 nm amorphous interface layer (SiOx and C) formed between the transferred 
LSMO and the Pt top electrode on the PMN-PT. The effect of this layer is neither investigated nor 
discussed but it must surely play a key role in that the adhesion of the LSMO to the substrate and 
therefore its response to strain changes must depend on the coupling thought the layer? Indeed, 
results using other polymers are evoked which suggest that the layer does come from the PDMS 
membrane. The supplemental information says that weak Van der Waals-like bonding occurs but then 
it is astonishing that a so weakly bonded layer transmits the high substrate strain to the LSMO. 
The authors also report the formation of cracks in the transferred LSMO film. The image in the 
supplemental information suggests that the average crack separation is about 10 micron. Why is there 
such a dense network of cracks when strain is supposed to be relaxed? When does the cracking 
happen? Do the cracks evolve as a function of strain? No link made with possible strain release or 
pinning and the magnetization response of the LSMO. The only discussion on the role of the cracks is 
some speculation on page 8 about the cracks defining areas of homogeneous magnetization. There is 
also a reference to extrinsic “enhancement of microstructural complexity” but it is not at all clear to 
what the authors are referring. 

The values for the strain states A and B are also puzzling. The strain along x in state B is 0.02% but in 
reference 47 the strain is closer to 0.1%, why is this? By the way something has gone wrong with the 
references, 41 and 47 are identical but with a different author list, I think that ref 47 is the correct list. 
In Figure 5 the PEEM images are not circular. 
My overall impression is that the work is interesting but the manuscript is sometimes superficial and 
one often has to go into the supplemental information to better understand what is going on. It may 
be that the manuscript would be better suited to a longer article. The two key points which must be 
addressed and require more discussion are the interface layer and the cracks in the film. 



Reviewer #3 (Remarks to the Author): 

In this study, the authors have transferred the epitaxial LSMO membranes on the Pt/PMN-PT 
substrates and performed an investigation on the multiferroic properties of heterostructures. They 
have shown an enhancement the saturation magnetization of freestanding LSMO membranes due to 
the release of epitaxial strain. Furthermore, they observed a large strain-mediated magnetoelectric 
coupling effect with an incoherent and non-covalent interfacial bonding between ferromagnetic layer 
and piezoactive substrate. The work is original and can be considered for publication after addressing 
the following points. 
1. The authors mentioned ‘…those transferred to flexible substrates have not been shown to display 
strain-induced changes of functional properties’, however, in a previous literature, the strain have an 
effect on the functional properties of the flexible La0.67Sr0.33MnO3 films (ACS Appl. Mater. Interfaces 
2019, 11, 22677−22683). This should be clarified. 
2. Calculation of the compressive strain in the out-of-plane direction of the LSMO layer in the 
LSMO/SRO/STO heterostructures seems necessary. Whether the stress in LSMO layer produces the 
cracks of flexible LSMO? The strain in the LSMO layer will relax by the LSMO thickness. So thicker 
LSMO layers with less strain will be beneficial to the magnetoelectric coupling effect in the 
LSMO/Pt/PMN-PT heterostructures. 
3. The temperature of the magnetization vs applied field lacks in Figure 1 (d). How about the Curie 
temperature of LSMO after transfer? 
4. In Figure S4, it can be seen that the boundary of the LSMO film during and after transfer is not 
sharp and a part of the LSMO films fall off. Dose this play a role in the value of the magnetization? 
Does the direction of cracks in the LSMO membranes change the anisotropy? 
5. Could amorphous layer between the LSMO and Pt influence the magnetoelectric coefficiency? How 
to control the thickness of amorphous layer? 
6. To better understand the origin of the film microstructure effect, the magnetic properties and 
magnetoelectric coupling properties with the LSMO grown directly on PMN-PT or the freestanding 
LSMO membranes free of cracks on PMN-PT, should be shown. 
7. There are some typos throughout the reference section that the authors must carefully proof 
(example – the ref.37).