Strength Of Magnetic Anisotropy Research Articles

Characterization of two dimensional ferromagnetic binary and Janus manganese dichalcogenides

We present a first-principles and anisotropic Heisenberg based study of electronic, finite temperature magnetic and thermal properties of two-dimensional binary MnX2 (X = S, Se, Te) and Janus MnXX′ (X, X′ = S, Se, Te) monolayers. All Mn dichalcogenides monolayers are dynamically stable with out-of-plane easy-axis ferromagnetic ground state. The ferromagnetic spin state is robust against external electric field. The strength of magnetic anisotropy is determined by the type of chalcogen atoms. The magnetic anisotropy can be tuned by an applied electric field in Janus Mn dichalcogenides monolayers contain heavy Te atom. The spin polarized electronic structure is strongly dependent on chalcogen atoms and varies from semiconductor (e.g. MnS2) to metallic (e.g. MnTe2) state. The dispersion relation of magnetic excited states is obtained by applying the linear order Holstein–Primakoff transformation to the anisotropic Heisenberg Hamiltonian. We find out high Curie temperature for Mn dichalcogenides by a self consistent calculation of magnetization as a function of temperature. Finally, at low temperature the phonon and magnon contribution to the heat capacity of Mn dichalcogenides are estimated as quadratic and linear temperature dependence, respectively.

XMCD and ab initio study of interface-engineered ultrathin Ru/Co/W/Ru films with perpendicular magnetic anisotropy and strong Dzyaloshinskii-Moriya interaction.

Understanding the nature of recently discovered spin-orbital induced phenomena and a definition of a general approach for "ferromagnet/heavy-metal" layered systems to enhance and manipulate spin-orbit coupling, spin-orbit torque, and the Dzyaloshinskii-Moriya interaction (DMI) assisted by atomic-scale interface engineering are essential for developing spintronics and spin-orbitronics. Here, we exploit X-ray magnetic circular dichroism (XMCD) spectroscopy at the L2,3-edges of 5d and 4d non-magnetic heavy metals (W and Ru, respectively) in ultrathin Ru/Co/W/Ru films to determine their induced magnetic moments due to the proximity to the ferromagnetic layer of Co. The deduced orbital and spin magnetic moments agree well with the theoretically predicted values, highlighting the drastic effect of constituting layers on the system's magnetic properties and the strong interfacial DMI in Ru/Co/W/Ru films. As a result, we demonstrate the ability to simultaneously control the strength of magnetic anisotropy and intermixing-enhanced DMI through the interface engineered inversion asymmetry in thin-film chiral ferromagnets, which are a potential host for stable magnetic skyrmions.

Anisotropy-exchange resonance as a mechanism for entangled state switching

We explore the three-particle spin model of an $S_{1}=\frac{1}{2}$ particle (e.g. a stationary electron) interacting with two spin-coupled $S_{\text{2,3}}$ particles with exchange coupling and magnetic anisotropy. We find that in the case of $S_{2,3}=1$ particles, the coupled particle entanglement states can be prepared, controlled, and read by the $S_{1}$ particle. We also find that for particular resonance conditions of the magnetic anisotropy strength $D$ and exchange coupling strength $J$, the entanglement state switching behavior is maximized and is robust against a range of anisotropic application of the exchange coupling.

Observation of uniaxial magnetic anisotropy and out-of-plane coercivity in W/Co20Fe60B20/W structures with high thermal stability

In this study, the development of uniaxial magnetic anisotropy (UMA) and out-of-plane coercivity (Hc┴) in W/Co20Fe60B20(CoFeB)/W structures by tuning the annealing temperature (TA) such as 300°C, 400°C and 500°C were achieved. For 400°C film, W and CoFeB interfaces play a major role in achieving the large Hc┴. Furthermore, the observation of large Hc┴ was found to be significantly induced by the interface on the two sides of CoFeB layer. The two-fold UMA strongly is stabilized in W/CoFeB/W trilayers up to 500°C. A maximum in-plane uniaxial anisotropy energy density (Ku) was observed for the 500°C annealed films, which is accompanied by the dominance of Hc┴ owing to the over-oxidation and/or occurrence of inter-diffusion across the interfaces. The oxidation and relieving of boron atoms in the CoFeB at higher annealing temperatures were confirmed by X-ray photoelectron spectroscopy (XPS). The control over the interface shared between the W and CoFeB is concluded to be essential in order to alter the strength of magnetic anisotropy. Hence, an investigation on W/CoFeB/W structures could be very beneficial for the modern Spin-Orbit Torque (SOT) based data storage applications and this inspires relevant research work to widen magnetic systems.

Large magnetocaloric effect in EuGd2O4 and EuDy2O4

Magnetization, heat capacity and direct measurements of the magnetocaloric effect show that EuGd2O4 and EuDy2O4 have a remarkably large magnetocaloric effect at cryogenic temperatures, owing to their high magnetic density and low ordering temperatures. The Gd derivative orders antiferromagnetically at TN = 4.6 K, while its magnetocaloric effect largely exceeds that of the reference refrigerant Gadolinium Gallium Garnet (GGG) above 5 K. The Dy derivative undergoes two phase transitions at TC1 = 3.65 K and TC2 = 4.7 K, respectively, which are the result of a peculiar magnetic arrangement: the first Dy sublattice is parallel to the crystallographic c-axis, while the Eu sublattice makes a variable angle from 0o to 45o with the direction of the second Dy sublattice that lies in the ab-plane. EuDy2O4 has a lower magnetocaloric effect than EuGd2O4, yet larger than GGG. Both ordering mechanisms are semi-quantitatively explained within the frame of a mean-field simulation, which takes into account the magnetic anisotropy strength of the participating magnetic ions.

High-frequency GMI hysteresis effect analysis by first-order reversal curve (FORC) method

In this work, we investigate the giant magnetoimpedance (GMI) hysteresis at high-frequency (10 MHz – 1 GHz) of Co-based amorphous magnetic ribbons. The first-order reversal curve (FORC) method was used to analyze their hysteretic behavior present at a low magnetic field (below 7 Oe). Results show that the GMI hysteresis is related to both the system magnetic anisotropy and the current frequency (through the skin depth). The GMI hysteresis gradually decreases upon frequency increase before disappearing, while a clockwise rotation of the FORC distributions is observed. These results are attributed to a heterogeneous magnetic structure in the magnetic ribbon volume. On the other side, while the cut-off frequency depends on the magnetic anisotropy strength, an inverted GMI hysteresis revives for the higher anisotropy ribbon. Above this frequency inversion, FORC results indicate a hardening of the effective switching field as a thicker region is probed. We propose that in this case, the stronger perpendicular anisotropy creates important differences between the superficial and volumetric anisotropy, enough to induce interaction between the two regions of different magnetization directions. This sensitive FORC protocol can be applied for investigating the GMI hysteresis, and thus the complex magnetic structure of several soft magnetic systems.

Static properties and current-induced dynamics of pinned90∘magnetic domain walls under applied fields: An analytic approach

Magnetic domain walls are pinned strongly by abrupt changes in magnetic anisotropy. When driven into oscillation by a spin-polarized current, locally pinned domain walls can be exploited as tunable sources of short-wavelength spin waves. Here, we develop an analytical framework and discrete Heisenberg model to describe the static and dynamic properties of pinned domain walls with a head-to-tail magnetic structure. We focus on magnetic domain walls that are pinned by 90$^\circ$ rotations of uniaxial magnetic anisotropy. Our model captures the domain wall response to a spin-transfer torque that is exerted by an electric current. Model predictions of the domain wall resonance frequency and its evolution with magnetic anisotropy strength and external magnetic field are compared to micromagnetic simulations.

In-plane spin canting and 1/3-magnetization-plateaulike behavior in S=3/2 Cr3+ kagome lattice antiferromagnets Cs2KCr3F12 and Cs2NaCr3F12

We have investigated the structural and magnetic properties of $S=3/2\phantom{\rule{4pt}{0ex}}{\mathrm{Cr}}^{3+}$ Heisenberg-like kagome lattice antiferromagnets ${\mathrm{Cs}}_{2}{\mathrm{K}}_{}{\mathrm{Cr}}_{3}{\mathrm{F}}_{12}$ and ${\mathrm{Cs}}_{2}{\mathrm{Na}}_{}{\mathrm{Cr}}_{3}{\mathrm{F}}_{12}$ using single crystals. Each compound has a slightly distorted kagome lattice, although the space groups differ for the two compounds. The magnetic data suggest that each compound exhibits the formation of antiferromagnetic ordering with in-plane-spin canting approximately below 6 K. The in-plane coplanar structures are clearly different from disordered ground states of the isostructural ${\mathrm{Ti}}^{3+}$ compounds and out-of-plane coplanar structures of the ${\mathrm{V}}^{3+}$ compounds, which is mainly caused by the differences in the strength of quantum fluctuation and the strength of magnetic anisotropy for these three spin systems. In contrast, as well as the ${\mathrm{Ti}}^{3+}$ and ${\mathrm{V}}^{3+}$ compounds, the magnetization curves show 1/3-magnetization-plateaulike anomalies.

Quantum-well-induced engineering of magnetocrystalline anisotropy in ferromagnetic films

Tuning quantum well states (QWSs) to govern physical properties in nanoscale leads to the development of advanced electronic devices. Here, we propose that QWSs can be engineered to control magnetocrystalline anisotropy energy (MCAE) which dominates the magnetization orientation (that is, the easy axis) of a ferromagnetic thin film. We investigate from first-principles the MCAE of the bcc Fe film on an Ag substrate. The calculated MCAE oscillates largely as Fe thickness increases agreeing well with experiments, and reaches oscillation extremes as the Fe d-orbital QWSs approach the Fermi level (EF). Crucially, we find that this phenomenon stems from the combined effect of intrinsic spin-orbit interaction (SOI) and Rashba SOI field on the Fe QWSs, which modulates the density of states at EF as the Fe thickness varies. Moreover, this effect offers a way to tune not only the strength of magnetic anisotropy but also the easy axis of a Fe film by shifting EF within ten meV via moderately charge injection, which could realize advanced memory devices with ultra-low power consumption.

Magnetic-anisotropy-induced spin blockade in a single-molecule transistor

We present a mechanism for a spin blockade effect associated with a change in the type of magnetic anisotropy over oxidation state in a single molecule transistor, by taking an example of an individual ${\mathrm{Eu}}_{2}{({\mathrm{C}}_{8}{\mathrm{H}}_{8})}_{3}$ molecule weakly coupled to nonmagnetic electrodes without linker groups. The molecule switches its magnetization direction from in-plane to out-of-plane when it is charged. In other words, the magnetic anisotropy of the molecule changes from easy plane to easy axis when the molecule is charged. By solving the master equation based on a model Hamiltonian, we find that current through the molecule is highly suppressed at low bias independently of gate voltage due to the interplay between spin selection rules and the change in the type of magnetic anisotropy. Transitions between the lowest magnetic levels in successive charge states are forbidden because the magnetic levels differ by $|\mathrm{\ensuremath{\Delta}}M|>1/2$ due to the change in the type of magnetic anisotropy, although the total spins differ by $|\mathrm{\ensuremath{\Delta}}S|=1/2$. This current suppression can be lifted by significant $\mathbf{B}$ field, and the threshold $\mathbf{B}$ field varies as a function of the field direction and the strength of magnetic anisotropy. The spin blockade effect sheds light on switching the magnetization direction by non-spin-polarized current and on exploring effects of this property coupled to other molecular degrees of freedom.

Magnetic excitations in quasi-one-dimensional helimagnets: Magnon decays and influence of interchain interactions

We present a comprehensive study of the magnetic properties of the long-range ordered quasi-one dimensional $J_{1}$-$J_{2}$ systems with a newly developed torque equilibrium spin-wave expansion approach, which can describe the spin Casimir and magnon decay effects in a unified framework. While the framework does not lose the generality, our discussion will be restricted to two representative types of inter-chain coupling systems: $J_{3}$- or $J_{4}$-system respectively. In spite of the long-range spiral order, the dynamical properties of these systems turn out to be highly nontrivial due to the incommensurate noncollinear spin configuration and the strong quantum fluctuation effects enhanced by the frustration and low-dimensionality. Both the systems show prominent spin Casimir effects induced by the vacuum fluctuation of the spin waves and related modification of the ordering vector, Lifshitz point's position and sublattice magnetization. Significant and spontaneous magnon decay effects are manifested in the quantum corrections to the excitation spectrum. By adjusting the strength of magnetic anisotropy and varying the approximation scheme, it is revealed that these striking distinct features are quite robust and have deep connection with both the spin Casimir and the magnon decay effects. Thus these special consequences of the inter-chain coupling on the spin wave dynamics may be served as a set of probes for different types of inter-chain couplings in experiments. At last, to guide experimental measurements such as inelastic neutron scattering in realistic materials and complement our theoretical framework, we develop the analytical theory of the dynamical structure factor within the torque equilibrium formulism and provide the explicit results of the quasi-one dimensional $J_{1}$-$J_{2}$ systems.

Surface morphology and magnetic property of wrinkled FeGa thin films fabricated on elastic polydimethylsiloxane

We investigated the surface morphology and the magnetic property of wrinkled Fe81Ga19 (FeGa) thin films fabricated in two different processes onto elastic polydimethylsiloxane (PDMS) substrates. The films obtained by directly depositing Ta and FeGa layers on a pre-strained PDMS substrate display a sinusoidally wrinkled surface and a weak magnetic anisotropy. The wavelength and amplitude of the sinusoidal morphology linearly increase with the metallic layer thickness, while the magnetic anisotropy decreases with increasing FeGa thickness. The other films grown by depositing FeGa layer on a wrinkled Ta/PDMS surface show a remarkable uniaxial magnetic anisotropy. The strength of magnetic anisotropy increases with increasing FeGa thickness. The magnetic anisotropy can be ascribed to the surface anisotropy, the magnetostrictive anisotropy, and the shape anisotropy caused, respectively, by the magnetic charges on wavy morphology, the residual mechanical stress, and the inhomogeneous thickness of FeGa films.

Interfacial exchange coupling and magnetization reversal in perpendicular [Co/Ni]N/TbCo composite structures.

Interfacial exchange coupling and magnetization reversal characteristics in the perpendicular heterostructures consisting of an amorphous ferrimagnetic (FI) TbxCo100–x alloy layer exchange-coupled with a ferromagnetic (FM) [Co/Ni]N multilayer have been investigated. As compared with pure TbxCo100–x alloy, the magnetization compensation composition of the heterostructures shift to a higher Tb content, implying Co/Ni also serves to compensate the Tb moment in TbCo layer. The net magnetization switching field Hc⊥ and interlayer interfacial coupling field Hex, are not only sensitive to the magnetization and thickness of the switched TbxCo100–x or [Co/Ni]N layer, but also to the perpendicular magnetic anisotropy strength of the pinning layer. By tuning the layer structure we achieve simultaneously both large Hc⊥ = 1.31 T and Hex = 2.19 T. These results, in addition to the fundamental interest, are important to understanding of the interfacial coupling interaction in the FM/FI heterostructures, which could offer the guiding of potential applications in heat-assisted magnetic recording or all-optical switching recording technique.

Relationship Between Magnetostriction and Magnetic Domain Structure in Fe-Based Alloy Single-Crystal Films With bcc(001) Orientation

Fe, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">95</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (at. %) single-crystal thin films of bcc(001) orientation are prepared on MgO(001) substrates using an ultrahigh-vacuum magnetron sputtering system. The influence of magnetic anisotropy on the magnetostriction under rotating magnetic field is investigated. Fe, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films show four-fold symmetries in in-plane magnetic anisotropy, where easy and hard magnetization directions are, respectively, observed along bcc[100] and bcc[110]. Higher saturation fields measured along bcc[110] are recognized in the order of Fe (6 kOe) > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (5 kOe) > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (4 kOe). Triangle output waveforms of magnetostriction appear when these films are measured under low-rotating fields. The behavior is related with the motion of 90° magnetic domain walls in magnetically unsaturated film. With increasing the rotating field, the films approach to magnetic saturations and the waveform gradually shifts to usual sinusoidal shape. Larger threshold rotating field is observed in the order of Fe > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , which is related to the saturation field. On the contrary, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">95</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> film possesses an almost isotropic property in in-plane measurement and shows sinusoidal waveforms even when the film is magnetically unsaturated. The waveform is affected by the symmetry and the strength of magnetic anisotropy.

Magnetostriction of fcc(110) single-crystal films of Ni-Fe, Ni, and Co under rotating magnetic fields

Ni-Fe, Ni, and Co(110) single-crystal films with uniaxial magnetic anisotropies are prepared on MgO(110) substrates by radio-frequency magnetron sputtering. The magnetostriction behavior under rotating magnetic fields is investigated. The Ni-Fe film shows waveforms consisting of a mixture of sinusoidal and triangular shapes under fields lower than 200 Oe. The peak of sinusoidal shape is observed when the field is applied along the easy magnetization axis, whereas that of triangular shape appears when the field is applied along the hard axis. With increasing the field from 200 to 300 Oe, the waveform changes to a usual sinusoidal shape. The waveform variation is related to the difference between the directions of uniaxial magnetic anisotropy and magnetization of magnetically unsaturated film. Waveforms consisting of sinusoidal and triangular shapes are also observed for the Ni and the Co films under low rotating fields. The threshold magnetic field where the shape changes to sinusoidal increases in the order of Ni-Fe < Ni < Co. The waveform is influenced by the symmetry and the strength of magnetic anisotropy.

Magnetic anisotropy in strained manganite films and bicrystal junctions

Transport and magnetic properties of La0.67Sr0.33MnO3 (LSMO) manganite thin films and bicrystal junctions were investigated. Epitaxial manganite films were grown on SrTiO3, LaAlO3, NdGaO3 (NGO), and (LaAlO3)0.3 + (Sr2AlTaO6)0.7 substrates, and their magnetic anisotropy were determined by two independent techniques of magnetic resonance spectroscopy. It was demonstrated that by using these techniques, a small (0.3%) anisotropy of crystal structure at the (110) surface plane of the orthorhombic NGO substrate leads to uniaxial magnetic anisotropy of the films in the plane of the substrate at least at the room temperature. It was found that on vicinal NGO substrates, the value of magnetic anisotropy strength can be varied in the range 100–200 Oe at T = 295 K by changing the substrate vicinal angle from 0° to 25°. Measurement of the magnetic anisotropy of manganite bicrystal junction demonstrated the presence of two ferromagnetic spin subsystems for both types of bicrystal boundaries with tilting of basal plane of manganite tilted bicrystal (TB-junction) and with rotation of crystallographic axes (RB-junction) used for comparison. The magnetoresistance of TB-junctions increases with decreasing temperature and the misorientation angle. Variation of bicrystal misorientation angle does not lead to change of misorientation of easy magnetic axes in the film parts forming TB-junction. Analysis of the voltage dependencies of bicrystal junction conductivity show that the low value of the magnetoresistance for the LSMO bicrystal junctions can be caused by two scattering mechanisms. The first one is the spin-flip of spin-polarized carriers due to the strong electron-electron interactions in a disordered layer at the bicrystal boundary at low temperatures and the second one is spin-flip by antiferromagnetic magnons at high temperatures.

Two different coercivity lattices in Co/Pd multilayers generated by single-pulse direct laser interference lithography

We report on magnetic structuring of Co/Pd multilayer films with strong perpendicular magnetic anisotropy by single-pulse direct laser interference lithography technique. Multibeam laser interference generates patterns of various types. The intense laser irradiation at interference maxima causes chemical intermixing at Co/Pd interfaces, leading to local changes in magnetic properties such as the creation of pinning centers and the reduction in the strength of magnetic anisotropy. We use magnetic force microscopy and Kerr microscopy to study the magnetization reversal processes in the patterned samples and find that the structures show three distinctly different behaviors depending on the intensity of the laser used for irradiation.

Magnetic characterization of cold rolled and aged AISI 304 stainless steel

Magnetic easy axis predicted by the orientation distribution of the maximum amplitude of magnetic Barkhausen emission (MBE), which is obtained by magnetization in radial directions from the center of the specimens has been applied to determine the magnetic anisotropy on cold rolled and aged 304 SS in two sets of specimen. The maximum of the MBE has been found to orient along the rolling direction (RD) compared to the transverse direction (TD), indicating the presence of magnetic easy axis along the rolling direction for both sets. The strain induced martensite phase transformation has been determined using X-ray diffraction technique. The orientation distribution function (ODF) analysis has been carried out to obtain the crystallographic texture with cold rolling. ODF analysis revealed the 〈110〉 texture as the major. The magnetic anisotropy factor has also been determined with cold deformation and noticed that the strength of magnetic anisotropy decreases above 50% deformation for both the sets. Results have been explained considering two competitive effects, formation of crystallographic texture in the martensite phase and presence of compressive residual stresses along RD during cold rolling.

Dynamic hysteresis behavior in epitaxial spin-valve structures

We report the dynamic hysteresis behavior of epitaxial single ferromagnetic fcc NiFe(001), fcc Co(001) layers, and fcc NiFe/Cu/Co(001) spin-valve structures investigated as a function of field sweep rate in the range of 0.01–270 kOe/s using the magneto-optic Kerr effect. The hysteresis loop area A is found to follow the scaling relation A∝Ḣα with α∼0.13 and ∼0.02 at low sweep rates and ∼0.70 and ∼0.30 at high sweep rates for 60 Å NiFe and 40 Å Co single magnetic layer structures, respectively. For the single and double spin valves, the “double-switching” behavior which occurs at low sweep rates transforms to “single switching” at ∼154 and ∼192 kOe/s, respectively. Our results provide direct experimental evidence that the magnetic anisotropy strength affects dynamic hysteresis scaling in ultrathin magnetic films.

Magnetization reversal dynamics in epitaxial spin-valve structures

We report the dynamic hysteresis behavior of epitaxial single ferromagnetic NiFe, Co layers, and NiFe/Cu/Co spin-valve structures investigated as a function of field sweep rate $\mathrm{H\ifmmode \dot{}\else \.{}\fi{}}(dH/dt)$ in the range 0.01--270 kOe/sec using the magneto-optic Kerr effect. In situ reflection high-energy electron-diffraction images confirmed that the NiFe, Cu, and Co layers grew epitaxially in the (100) orientation where the fcc NiFe, Co〈110〉 in-plane directions correspond to the Si〈100〉 directions. For $\mathrm{Cu}/60\AA{}\mathbf{NiFe}/\mathrm{C}\mathrm{u}/\mathrm{S}\mathrm{i}{(H}_{c}=5\mathrm{Oe})$ and $\mathrm{Cu}/40\AA{}\mathbf{Co}/\mathrm{C}\mathrm{u}/\mathrm{S}\mathrm{i}{(H}_{c}=104\mathrm{Oe})$ single magnetic layer structures, the hysteresis loop area A is found to follow the scaling relation $A\ensuremath{\propto}{H}^{\ensuremath{\alpha}}$ with $\ensuremath{\alpha}\ensuremath{\sim}0.13$ and \ensuremath{\sim}0.02 at low sweep rates and \ensuremath{\sim}0.70 and \ensuremath{\sim}0.30 at high sweep rates, respectively. This result indicates that the NiFe and Co layers in the spin-valve structures can be expected to show distinct scaling behavior at high sweep rate. We found that the ``double-switching'' behavior which occurs at low sweep rates transforms to ``single switching'' at \ensuremath{\sim}154 kOe/sec and \ensuremath{\sim}192 kOe/sec, respectively, for the single and double spin valves due to the different dynamic response of the NiFe and Co layers. Our results provide direct experimental evidence that the magnetic anisotropy strength affects dynamic hysteresis scaling in ultrathin magnetic films, in contrast with the predictions of current theoretical models.