Interface Effects on Magnetic Anisotropy and Domain Wall Depinning Fields in Pt/Co/AlO_x Thin Films

Round 1

Reviewer 1 Report

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Reviewer 2 Report

Magnetic films with an easy magnetization axis perpendicular to the plane are of interest for applications (high-density magnetic recording, an effective medium for skyrmion manipulation, etc.). In this work, three-layer Pt/Co/AlOx, with a cobalt layer about 1 nm thick, are prepared by magnetron sputtering at room temperature with a high vacuum in a sputtering chamber. The magnetic properties studied for a number of samples with different thicknesses of the Al layer showed that in general there is well-pronounced perpendicular magnetic anisotropy, but the coercivity and the motion parameters of the domain walls changes nonmonotonically. A sample with an Al thickness of 5 nm is clearly distinguished, where the maximum Hc and depinning field are achieved, as well as the minimum velocity of domain walls. The authors discuss the results obtained as an effect of interfacial effects and surface roughness of thin films. The original experimental material, as well as the demonstration of some unusual approaches to the measurement of magnetic parameters, make the material interesting enough to be recommended for publication in Magnetochemistry. I will make a number of remarks that should probably be taken into account before the final accept.

 

1. In the experimental section, the films are reported to be annealed at 460C. Such heat treatment can lead to both diffusion and solid-state reactions (for example [Myagkov V G, Bykova L E, Zhigalov V S, Matsynin A A, Velikanov D A and Bondarenko G N 2021 Solid-state synthesis, rotatable magnetic anisotropy and characterization of Co1-xPtx phases in 50Pt/50fccCo(001) and 32Pt/68fccCo(001) thin films J. Alloys Compd. 861 157938]). In the text, the Co layer is referred to as pure or slightly oxidized. The only parameter by which one can judge the state of the cobalt layer is the magnetization. The decrease relative to pure cobalt may be due not to oxidation, but to the formation of intermetallic compounds (for example, Co3Pt). This possibility is worth at least touching on in the discussion.

2. Aluminum thickness of 5 nm stands out using Hc at room temperature. Fig. 3b shows that at other temperatures, the maximum Hc will be achieved at other thicknesses. If the authors have an idea why this is the case, it would be helpful to add it to the discussion.

3. The amplitude of the irregularities is comparable to the thickness of the cobalt layer. This is not so bad if the lateral dimensions of the irregularities are much larger than their height. Unfortunately, there is no rating that would show this.

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Reviewer 3 Report

This work studies the static magnetic properties of perpendicularly-magnetized (PMA), asymmetric Pt/Co/AlOx trilayers, with a special focus on the dependence of the domain wall depinning field and the domain wall velocity with the thickness and temperature. Extensive characterizations were conducted on the series of the samples, including magnetometer, transport, imaging and cross-section TEM. The material characterizations along with the robust magnetic properties indicate the good quality of the samples. In particular, the study of the AlOx thickness-dependence provide useful dataset and guidance for similar PMA structures and related applications. The work is overall comprehensive, interesting, and useful to the community. A few minor issues need to be addressed before the final publication of the manuscript:

(1) The non-monotonic behavior was observed for the depinning field versus the AlOx thickness. It's an interesting result but the authors did not comment on why. An interpretation, even plausible, would be helpful to improve the understanding of the system.

(2) The authors mentioned the importance of FM layer oxidation to the depinning of DWs. Since the authors have TEM capability, can such an information be also derived from the TEM imaging dataset?

(3) Likewise, discussions on Fig. 3a and b was a bit lacking. At 35K, the 3.6-nm sample distinguishes itself a lot from other thicknesses, as characterized by much sharper switchings. Why such a thickness is unique? 

 

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