We perform a detailed comparative study of conventional transverse magneto-optical Kerr effect (T-MOKE) measurements and a methodology that utilizes an effective polarization detection scheme for ...mixed s- and p-polarized incoming light. To test the ultimate sensitivity of both methods, we also design a series of specialized samples in which the T-MOKE signal of a Co-film is artificially reduced by means of a Ag overcoat of varying thickness. We find that the effective polarization detection scheme leads to a more than 30-fold increase of the T-MOKE signal and signal-to-noise ratio, even under general operation conditions which were not individually optimized. This allowed for the observation of T-MOKE hysteresis loops of Co-films that were buried under 80 nm of Ag, for which the MOKE signal was only 1/600 of that for an uncoated Co-film. In comparison, conventional T-MOKE measurements did not succeed for Ag overcoats thicker than 40 nm.
We demonstrate, as proof of concept, a materials design path that allows us to exploit thermal deposition technique to fabricate sodium (Na) metal anodes at the microscale. Our study reveals that Na ...thin anodes <10 μm, directly coated on a stainless-steel current collector, reduces the energy barrier of Na nucleation during plating process. Likewise, evaporated thin-film sodium anodes enable achieving a cycling in a full battery configuration as stable as with bulk Na anode, and considerably more stable than the here presented anode-less case. These insights may lead to practical design changes toward the efficient use of metallic Na, alleviating weight and costs. In addition, they provide a solid starting point for future developments that focus on improving the stability and extending the life of Na-metal batteries. All this paves the way for the next-generation of sodium-based energy storage technologies, where energy density and cost are key factors.
•Thermal evaporation is successfully used to fabricate high quality and homogeneous Na thin (<10 μm) anodes at the microscale.•Evaporated Na thin anodes lower both the energy barrier of Na nucleation during plating processes and the charge transfer resistance.•The developed Na thin anode ensure stable galvanostatic cycling against sustainable cathode material.•Our innovative concept promotes widely accessible (nano-) microscale thin metallic alkali electrodes design.
We present a study of the magnetic properties of Co(3.0 nm)/Pt(0.6nm)N multilayers as a function of Co/Pt bilayer repetitions N. Magnetometry investigation reveals that samples with N ≥ 15 exhibit ...two characteristic magnetization reversal mechanisms, giving rise to two different morphologies of the remanent domain pattern. For applied magnetic field angles near the in-plane field orientation, the magnetization reversal proceeds via a spontaneous instability of the uniform magnetic state resulting in perpendicular stripe domains. Conversely, for field angles close to the out-of-plane orientation, the reversal occurs via domain nucleation and propagation leading to a mazelike domain pattern at remanence. Our measurements further enable the characterization of the N-dependent energy balance between the magnetic anisotropy and magnetostatic energy contributions, revealing a gradual disappearance of the domain nucleation process during magnetization reversal for N < 14. This leads to the exclusive occurrence of an instability reversal mechanism for all field orientations as well as alignedlike stripe domains at remanence. Furthermore, a detailed study of the influence of the magnetic history allows the determination of a range of material properties and magnetic field strengths, where a lattice of bubble domains with remarkably high density is stabilized. These modulations of the ferromagnetic order parameter are found to strongly depend on N, in terms of center-to-center bubble distance as well as of bubble diameter. Moreover, such Co/Pt multilayers could be utilized to engineer field reconfigurable bubble domain lattices, which resemble magnonic crystals.
The high-energy ball milling method has been used to synthesize the polycrystalline powders La
0.5
Ca
0.5
Mn
1−
x
V
x
O
3
(
x
= 0.05,
x
= 0.10). The Rietveld refinement technique shows that the ...samples crystallized in the orthorhombic structure with the
Pbnm
space group. The La
0.5
Ca
0.5
Mn
0.95
V
0.05
O
3
exhibits a second-order phase transition from paramagnetic (PM) to ferromagnetic (FM) state at
T
C
= 208 ± 1 K followed by a second one from FM to charge ordering–antiferromagnetic state at
T
N
= 150.0 ± 0.1 K when decreasing temperature. The substituted sample with 10% amount of vanadium dopant corresponds to the disappearance of the charge-order phase; meanwhile, it was suppressed for 5% of the vanadium in the solid-state route. The Curie temperature
T
C
increases with vanadium content from 208 ± 1 K for
x
= 0.05 to 255 ± 1 K for
x
= 0.10. The values of the maximum of the magnetic entropy change under a magnetic field change of 5 T are found to be 2.95 ± 0.04 J kg
−1
K
−1
and 5.42 ± 0.07 J kg
−1
K
−1
corresponding to a relative cooling power RCP = 128.4 ± 0.3 and 220.8 ± 0.7 for
x
= 0.05 and
x
= 0.10 respectively. The order of phase transition has been determined. The critical exponent study has been performed for La
0.5
Ca
0.5
Mn
0.9
V
0.10
O
3
by using the Arrott plot, Kouvel–Fisher method, and critical isotherm analysis. The measured β,
γ
, and
δ
values are in agreement with those expected for the tricritical mean-field model.
We experimentally explore the orientation dependence of the magnetization in single-crystal Co0.77 Ru0.23 alloy films and demonstrate that the material remains magnetically anisotropic near and even ...above the Curie temperature TC , which is incompatible with the conventional description of anisotropy via temperature-dependent anisotropy constants. To accomplish an appropriate description of magnetic anisotropy at all temperatures, we derive an improved, but still simple free-energy description based upon the anisotropic Heisenberg model that is in excellent agreement with our experimental data.
In this work we report on the magnetocaloric effect of La2/3Ca1/3MnO3 (LCMO) and La2/3Ca1/3Mn0.94Cr0.06O3 (LCMCrO) manganite thin films grown by DC magnetron sputtering on LaAlO3 (100) substrates. ...X-ray diffraction shows that both doped and undoped films crystallize in the orthorhombic structure. Magnetic measurements show a decrease in both the Curie temperature, TC, and the saturation magnetization, MS, for the LCMCrO sample. The change in the magnetic entropy (ΔSm) was extracted from hysteresis loops at different temperatures around the ferromagnetic to paramagnetic transition, displaying a maximum of entropy change (ΔSm)max near TC in both films. Moreover, a shift in (ΔSm)max toward temperatures above TCwith increasing magnetic field and a broadening of the entropy change curve were observed. Results of refrigeration cooling power show a lower efficiency for LCMCrO. In order to obtain a local insight into the magnetic interactions of these films, measurements of X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) were performed. XMCD suggests that an antiferromagnetic coupling between Mn4+ - Mn3+ is favored with Cr3+ incorporation, which reduces the Mn L2,3 XMCD signal and results in a decrease of MS and (ΔSm)max in LCMCrO films.
In this work, we investigate the thermodynamic behavior of exchange graded ferromagnetic films using Monte Carlo simulations. The systems are modeled by using a classical Heisenberg Hamiltonian, ...considering only nearest neighbor exchange interactions and a linear depth-dependent effective magnetic exchange coupling strength profile. Our quantitative assessment of the local physical quantities shows that each layer exhibits rather isolated thermodynamic behavior, since both layerwise magnetization and susceptibility data indicate layer-specific "local" Curie temperatures as a consequence of the depth-dependent change in the exchange coupling strength. We also propose and evaluate a predictive formulation for such profiles of "local" Curie temperatures, whose only input is the pre-selected exchange coupling profile. Having this very precise predictive tool, we show how it can be used to obtain the temperature-dependent ferromagnetic state including its depth-dependent magnetization profile at any given temperature. Thus, it is possible to predict which exchange profile will produce a desired thermodynamic behavior and associated functionality, without the need to perform complex experiments or time-consuming computations. With this study, we furthermore demonstrate that nonlocal aspects of the thermodynamic state formation in graded magnetic materials are relevant only over very short length scales, which is in outstanding qualitative agreement with prior numerical and experimental work.
Although ferromagnetism is in general a long-range collective phenomenon, it is possible to induce local spatial variations of magnetic properties in ferromagnetic materials. For example, systematic ...variation of the exchange coupling strength can be used to create systems that behave as if they are composed of virtually independent segments that exhibit “local” Curie temperatures. Such localization of thermodynamic behavior leads to boundaries between strongly and weakly magnetized regions that can be controllably moved within the material with temperature. The utility of this interesting functionality is largely dependent on the inherent spatial resolution of magnetic properties, specifically the distance over which the exchange strength and corresponding properties behave locally. To test the degree to which this type of localization can be realized in materials, we have fabricated epitaxial films of Co1−xRux alloy featuring a nanometer-scale triangular wavelike concentration depth profile. Continuous nanoscale modulation of the local Curie temperature was observed using polarized neutron reflectometry. These results are consistent with mean-field simulations of spin systems that encompass the possibility of delocalized exchange coupling and show that composition grading can be used to localize magnetic properties in films down to the nanometer level. Since this is demonstrated here for an itinerant metal, we assert that for virtually any modulated magnetic material system, collective effects can be suppressed to length scales smaller than about 3 nm, so that magnetic behavior overall can be well described in terms of local material properties.
We study theoretically and experimentally the influence of the light incidence angle φ0 on the precision of generalized magneto-optical ellipsometry (GME). A brief review of the GME methodology is ...presented together with a study of the error propagation from measurement uncertainties to the precision of the resulting complex index of refraction N and magneto-optical constant Q. The results are compared with longitudinal GME measurements on bulk polycrystalline cobalt. We observe a strong increase of the resulting relative error as φ0 decreases below 45°. We tested our theoretical estimates by performing GME measurements for polycrystalline cobalt (N=2.20+3.42i; Q=(2.25−0.80i)×10−2)) and found GME measurements to clearly exhibit improved reliability for φ0>30°.
•A brief review of generalized magneto-optical ellipsometry is presented.•We calculate the propagation of uncertainties on the magneto-optical constants.•Decreasing incidence angle increases the uncertainty propagation.•We perform measurements on bulk cobalt films which confirm our predictions.
Artificial ferromagnetic (FM)/nonmagnetic multilayers, with large enough FM thickness to prevent the dominance of interface anisotropies, offer a straightforward insight into the understanding and ...control of perpendicular standing spin wave (PSSW) modes. Here we present a study of the static and dynamic magnetic properties of Co(3.0 nm)/Au(0.6 nm)1 ≤ N ≤ 30 multilayers. Magnetometry reveals that the samples exhibit magnetization reversal properties typical of an effective single layer with weak perpendicular anisotropy, with the distinctive thickness-dependent magnetization reorientation transition from uniform in-plane to out-of-plane stripe domains at remanence. However, when such multilayer systems are out-of-plane saturated, the dynamic response reveals the existence of several different ferromagnetic resonances in the form of PSSW modes that strongly depend on the material modulation characteristics along the total thickness. These modes are induced by the layer stacking itself as the effective single layer model fails to describe the observed complex dynamics. In contrast to most systems considered in the past, described by a dynamic model of a single effectively homogeneous thick layer, the specific structures investigated here provide a unique platform for a large degree of tunability of the mode frequencies and amplitude profiles. We argue that the combination of periodic magnetic properties with vertical deformation gradients, arising from heteroepitaxial strain relaxation, converts the Au interlayer regions into a vertical regular array of magnetic pinning planes for the PSSW modes, which promotes the complex dynamics observed in this system.
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