Preparation, Characterization, and Modeling of Ultrahigh Coercivity Sm–Co Thin Films

Abstract

on the requirements of the specifi c application and the compatibility of processing conditions with fi lm integration. There have been many more reports on the fabrication of Nd-Fe-B based fi lms [3][4][5] compared to Sm-Co based fi lms, [6][7][8][9][10] which may be attributed to a drive towards maximizing the remanence and thus the energy product of the hard magnetic fi lm. However, in certain applications where the hard magnetic fi lm is exposed to high demagnetizing fi elds and/or high operating temperatures, Sm-Co fi lms would be a better choice, due to the much higher values of magneto-crystalline anisotropy and thus high coercivity achievable in Sm-Co based materials. [11][12][13][14] We previously reported on the fabrication of high coercivity Sm-Co thin fi lms ( µ 0 H c ≤ 5 T at 300 K) by triode sputtering. [ 6 ] In this paper we demonstrate that the coercivity of Sm-Co based fi lms can be signifi cantly increased through a modifi cation of the target composition. With the aim to gain a better understanding of the origin of the high coercivity values, we carried out high-resolution microstructural characterization by using scanning transmission electron microscopy and atom probe tomography, and simulated the effect of the observed microstructural defects on magnetization reversal. While the high value of coercivity that was achieved could be relevant for particular applications, combined exploitation of recent advances in sample preparation, characterization, and modeling should contribute to the engineering of better bulk magnets. ResultsThe GI-XRD patterns of samples #1, #2, and #3 are shown in Figure 1 (note that all samples are amorphous in the asdeposited state -data not shown). Comparison of experimental peak positions with powder diffraction data fi les indicates that the crystal structure of the annealed fi lms changes from SmCo 1:7 to 1:5 and then to 2:7 as the Sm content of the layer is increased. Hereafter, samples "#1", "#2", and "#3" will be identifi ed as fi lms of 1:7, 1:5, and 2:7, respectively. Corresponding c / a ratios of 0.82, 0.795, and 0.808 were calculated from XRD peak positions for 1:7, 1:5, and 2:7, respectively. These values are quite close to the actual values for 1:7, 1:5, and 2:7 phases, namely 0.816, 0.793, and 0.803, respectively. [ 15 ] The as-deposited fi lms show soft magnetic behavior ( Figure 2 a). Room temperature in-plane hysteresis loops of

The influence of grain morphology and easy axis orientation on the coercivity of Sm(Co0.9Cu0.1)5 thin films

“…10 and E static expression. Its long-range feature was experimentally confirmed in the Ta spacer of Nd 2 Fe 14 B/α-Fe multilayer films [34]. For simplicity, the total coupling energy in different c-axis geometries between neighboring hard-magnetic moment m h and soft-magnetic moment m 0,0 are compared in Fig.…”

Novel Bimorphological Anisotropic Bulk Nanocomposite Materials with High Energy Products

“…We further determined the coercivity mechanism of the material that involves domain‐wall pinning (Figure S3, Supporting Information). This result is likely to originate from the abundant grain boundaries from the small nanosized hard and soft grains that increase the number of domain‐wall‐pinning sites; moreover, the observed SmCo 3 phase (≈9 wt% determined by XRD studies) in the material may also contribute to the strong pinning behavior by increasing grain boundary fraction or forming stacking faults as pining centers, as demonstrated in recent studies of ultrahigh coercivity Sm−Co thin films . This result suggests the way to enhance the coercivity of the materials by increasing domain‐wall‐pinning strength and sites.…”

“…It should be mentioned that although our nanocomposites show a comparable energy product with the existing single‐phase SmCo 5 and Sm 2 Co 17 magnets, they have a lower coercivity (4.6 kOe) and only partially aligned hard‐phase grains. This low coercivity could be significantly enhanced by generating the heterogeneities with SmCo 3 nanograins and stacking faults in the materials, as demonstrated in the recent study of ultrahigh coercivity Sm−Co thin films, where abundant grain boundaries (phase interfaces) and the SmCo 3 stacking faults are identified as strong domain‐wall‐pinning sites (centers). Engineering strain‐energy anisotropy and temperature gradient in the deformation process will be the key to sufficiently align the hard‐phase grains (see below).…”

Engineering Bulk, Layered, Multicomponent Nanostructures with High Energy Density

“…This small coercivity could potentially be enhanced by engineering the layered structure such as the interlayer space and nanostructure within the layers. For example, a promising approach may be to introduce nanoscale heterogeneities and stacking faults within the layers, as has been demonstrated in recent studies of SmCo materials with high coercivity . We anticipate that more superior magnetic properties will be realized once the disadvantages—in other words, partially aligned hard‐phase grains and low coercivity—are overcome, because a larger energy product (≥39 MGOe) has been achieved in thin‐film model materials such as SmCo 5 /Fe and Nd 2 Fe 14 B/FeCo …”