Nonmagnetic Interlayer Research Articles

Magnetic properties and hysteresis loops of a mixed spin-1/2 and spin-3/2 bilayer with non-magnetic inter-layers

Magnetic properties and hysteresis loops of a mixed spin-1/2 and spin-3/2 bilayer with non-magnetic inter-layers

Peculiarities of Hysteretic Properties and Magnetostriction of Nano-Structured Fe10Ni90 Films

The study is related to the investigation of hysteresis and magnetostrictive properties of single-layer Fe10Ni90 films and nano-structured [Fe10Ni90/Cu]p/Fe10Ni90 films, where the magnetostrictive layers are separated with a nonmagnetic interlayer. The magnetostriction effect is shown to depend on the total layer thickness; in this case, the magnetostriction of the [Fe10Ni90/Cu]p/Fe10Ni90 film structures was found to be higher than that of the single-layer Fe10Ni90 films. The observed peculiarity is associated with weakening the fixing effect of a substrate.

Layer-resolved vector magnetometry using generalized magneto-optical ellipsometry

We demonstrate the ability of a single magneto-optical reflection experiment to achieve layer-resolved vector magnetometry in multilayer films. For this purpose, we designed, fabricated, and measured a set of epitaxial ferromagnetic/non-magnetic/ferromagnetic heterostructure multilayer samples that exhibit in-plane uniaxial anisotropy and a tunable ferromagnetic interlayer coupling strength through the non-magnetic interlayer. By means of generalized magneto-optical ellipsometry measurements, we obtain the magnetization angles of the two different ferromagnetic layers independently as a function of the applied field. Hereby, we observe that the magnetization switching of one layer can trigger a discontinuous shift of the magnetization angle in the second layer if ferromagnetic interlayer coupling is present. Moreover, we reproduce the obtained behavior using a model of two coupled macrospins, which corroborates even the unexpected aspects of our experimental results and thus reinforces the sensitivity and reliability of our experimental layer-resolved vector magnetometry.

Magneto-optical detection of non-collinear magnetization states in ferromagnetic multilayers

We have experimentally studied the relationship in between non-collinear magnetization states in ferromagnetic (FM) multilayers and their resulting magneto-optical (MO) properties. Hereby, we observe that the phase of the complex-valued MO parameters are especially sensitive towards non-collinear magnetization states and enable their unambiguous detection. For the purpose of our experimental study, we designed, fabricated and characterized a set of epitaxial FM/NM/FM multilayers with in-plane uniaxial anisotropy, in which the non-magnetic (NM) interlayer thickness t was varied, so that tunable FM interlayer exchange coupling strength in between the two FM layers could be achieved. Furthermore, the two FM layers were made from different alloys, so that they exhibit different levels of magnetocrystalline anisotropy, which enables a collinear to non-collinear magnetization state transition upon applying a magnetic field H away from the in-plane easy axis for samples with sufficiently large t . Utilizing generalized MO ellipsometry, we determined the full reflection matrix R as a function of H and we observed that the phases of the complex-valued MO coefficients in R change with H in multilayers that have sufficiently weak interlayer coupling strength, i.e. large t, which can only happen if non-collinear magnetization states of varying non-collinearity occur in those samples. For samples with small t, corresponding to strongly exchange coupled FM layers, this effect is absent, consistent with the existence of collinear magnetization states in those multilayers for all H values.

Interlayer Interaction and Coercivity of Three-Layer Films Оbtained bу Chemical Deposition

Abstract—The results of experimental and theoretical studies of the coercivity and the displacement field of the hysteresis loop on the thickness of the nonmagnetic interlayer in magnetic films obtained by electroless plating are presented. With the help of model calculations based on the Landau–Ginzburg equations, the exchange interactions between magnetic layers with the participation of atoms of the nonmagnetic layer are studied. The resulting expression for the displacement field describes well the exponential changes in the displacement field as a function of the interlayer thickness in structures with both magnetically soft layers and layers with significantly different values of the coercivity.

Spacer Thickness and Temperature Dependences of the Interlayer Exchange Coupling in a Co/Pt/Co Three-Layer Structure

Domain wall mobility as a function of nonmagnetic interlayer thickness and temperature was studied in ultrathin exchange-coupled ferromagnetic layers using magneto-optic Kerr microscopy. The system under study is a Pt/Co/Pt/Co/Pt heterostructure having perpendicular magnetic anisotropy and a middle Pt layer with spatially variable thickness. The ferromagnetic interaction between the Co layers is observed when the Pt interlayer thickness varies from 5 to 6 nm in a temperature range of 200–300 K. There is a certain interval of Pt layer thickness where domain walls in both ferromagnetic layers move independently. Nonlinear dependence of the domain wall displacement on the applied field was measured. It is shown that an equilibrium position of the relaxed domain wall depends on field, temperature, and the nonmagnetic interlayer thickness. This position is determined by the energy balance: (i) domain wall displacement provided by the applied field, (ii) interlayer exchange interaction in the area swept by the domain wall, and (iii) domain wall coercivity. The mechanism of domain wall stabilization in terms of independent wall motion near critical thickness was considered. It is found that both the coercivity of the Co layer and the critical thickness decrease at higher temperature, while the interlayer exchange constant J is changed weakly.

Influence of the thickness of a nonmagnetic layer on the coupled dynamics of magnetic vortices in a spin-transfer nanooscillator

A spin torque nano-oscillator in the form of a three-layer magnetic tunneling junction of small diameter (120 nm), where the magnetizations in both magnetic layers are in vortex state, is considered. The effect of the thickness of a nonmagnetic layer on the coupled dynamics of two magnetic vortices in a spin torque nano-oscillator has been studied. The thick permalloy magnetic layer has a thickness of 15 nm, the middle non-magnetic layer has a thickness in the first case of 12.5 and in the second 15 nm, and the thin permalloy magnetic layer has a thickness of 4 nm. Numerical calculation of the dynamics of magnetostatically coupled vortices was carried out using the software package SpinPM for micromagnetic modeling. The features of the vortex motion dynamic are studied for different thicknesses of the nonmagnetic interlayer. It is shown that in all cases of thickness of the nonmagnetic interlayer, three regimes of vortex dynamics are observed: the oscillations of magnetic vortices damped over time, the mode of stationary coupled oscillations of magnetic vortices, and regime, when vortices “leave” the edge of the disk. It is found that increasing in the thickness of the nonmagnetic layer leads to decreasing in the values of the first, second, and third critical currents.

First-principles Calculations of Magnetic Anisotropy of Fe and Co Films, Separated by Nonmagnetic Metallic Interlayers

First-principles Calculations of Magnetic Anisotropy of Fe and Co Films, Separated by Nonmagnetic Metallic Interlayers

Magnetic-field tuning of the spin dynamics in the magnetic topological insulators(MnBi2Te4)(Bi2Te3)n

We report a high frequency/high magnetic field electron spin resonance (HF-ESR) spectroscopy study in the sub-THz frequency domain of the two representatives of the family of magnetic topological insulators (MnBi$_{2}$Te$_{4}$)(Bi$_{2}$Te$_{3}$)$_{n}$ with $n = 0$ and 1. The HF-ESR measurements in the magnetically ordered state at a low temperature of $T = 4$ K combined with the calculations of the resonance modes showed that the spin dynamics in MnBi$_{\text{4}}$Te$_{\text{7}}$ is typical for an anisotropic easy-axis type ferromagnet (FM) whereas MnBi$_{\text{2}}$Te$_{\text{4}}$ demonstrates excitations of an anisotropic easy-axis type antiferromagnet (AFM). However, by applying the field stronger than a threshold value $\sim 6$ T we observed in MnBi$_{\text{2}}$Te$_{\text{4}}$ a crossover from the AFM resonance modes to the FM modes which properties are very similar to the ferromagnetic response of MnBi$_{\text{4}}$Te$_{\text{7}}$. We attribute this remarkably unusual effect unexpected for a canonical easy-axis AFM, which, additionally, can be accurately reproduced by numerical calculations of the excitation modes, to the closeness of the strength of the AFM exchange and magnetic anisotropy energies which appears to be a very specific feature of this compound. Our experimental data evidences that the spin dynamics of the magnetic building blocks of these compounds, the Mn-based septuple layers (SLs), is inherently ferromagnetic featuring persisting short-range FM correlations far above the magnetic ordering temperature as soon as the SLs get decoupled either by introducing a nonmagnetic quintuple interlayer, as in MnBi$_{\text{4}}$Te$_{\text{7}}$, or by applying a moderate magnetic field, as in MnBi$_{\text{2}}$Te$_{\text{4}}$, which may have an effect on the surface topological band structure of these compounds.

Domain Structure and Magnetization Reversal in Multilayer Structures Consisting of Thin Permalloy Films Separated with Nonmagnetic Interlayers

Domain Structure and Magnetization Reversal in Multilayer Structures Consisting of Thin Permalloy Films Separated with Nonmagnetic Interlayers

A Decrease in the Exchange Bias Caused by an Increase in the Effective Thickness of the Copper Layer in the NiFe/Cu/IrMn Heterostructures

In a series of NiFe/Cu/IrMn structures with a variable effective thickness of the nonmagnetic copper interlayer (up to its absence in the NiFe/IrMn sample), we observed a decrease in the exchange bias and coercive force with an increase in the effective thickness of the copper layer. The coalescence of copper islands when the effective thickness of the copper layer reaches 1 nm changes the contact exchange interaction between the ferromagnet and antiferromagnet in NiFe–IrMn to indirect exchange interaction through the conduction electrons of the copper layer in NiFe–Cu–IrMn. The structural quality of single-crystal ferromagnetic and antiferromagnetic layers does not change, and the magnetization reversal occurs without the participation of domains in the temperature range of 2–300 K. Simulation of the deposition dynamics demonstrates the island structure of the film at the initial stages up to an effective thickness of 1 nm.

Exchange Interactions in NiFe/Ta/IrMn Heterostructures under Conditions of Tantalum Deficiency

In the NiFe/Ta/IrMn structures, the contributions of two types of exchange interactions at the NiFe/IrMn interface, partially separated by sections of the nonmagnetic tantalum interlayer, are distinguished. One type of exchange is “contact”—it occurs directly at the NiFe/IrMn interface. Another type is “interlayer,” which takes place through the conduction electrons of the tantalum interlayer. A comparison of the temperature dependences of the exchange bias of the hysteresis loops at fixed parameters of the ferromagnetic layers and various effective thicknesses of the nonmagnetic interlayer made it possible to separate the contributions of the above types of exchange interactions and determine their temperature dependences individually. The exchange interaction energies at the NiFe/IrMn and NiFe/Ta/IrMn interfaces were determined.

Уменьшение обменного смещения, вызванное ростом эффективной толщины слоя меди в гетероструктурах NiFe/Cu/IrMn

In a series of NiFe/Cu/IrMn structures with variable effective thickness of the nonmagnetic copper interlayer (up to its absence in the NiFe/IrMn sample), decrease the exchange bias and coercivity caused by increase in the effective thickness of the copper layer is observed. Merger of copper islands at the 1 nm effective Cu thickness replaces direct exchange interaction between the ferromagnetic NiFe and antiferromagnetic IrMn to indirect exchange interaction provided by the conduction electrons through the copper layer NiFe-Cu-IrMn. The structural quality of single crystalline ferro- and antiferromagnetic layers does not undergo any change and magnetization reversal happens by coherent rotation of magnetization in the all analyzed temperature range 2 - 300 K. Simulation of the dynamics of Cu deposition demonstrates the island structure of the film at the initial stages up to effective thickness 1 nm.

Thickness dependences of coercivity in three layer films obtained by chemical deposition

The change of the coercivity Hc of three-layer films obtained by chemical deposition depending on the thickness of the nonmagnetic interlayers and magnetic layers are presented. Structures with magnetically identical soft layers, as well as with significantly different HC values were investigated. It was established that in both cases thecoercivity decreases with the interlayer thickness increasing by an exponential law. It is consistent with a change in the displacement field of the hysteresis loop. The observed changes in the parameters of the hysteresis loop are associated with the roughness of the interfaces.

Interlayer modulation on the dynamic magnetic properties of L1-FePt/NM/[CoNi]5 composite film structures

The magnetization precession dynamics is systematically studied in L10-FePt/NM/[CoNi]5 exchange-coupled films using the time-resolved magneto-optical Kerr effect technique, where the nonmagnetic interlayer is Ta or Pt. It is demonstrated that the precession frequency f decreases dramatically with the increasing interlayer thickness of Ta (tTa) or Pt (tPt). By fitting the f ∼ H curves of different tTa with the coherent precession model including the interfacial coupling interaction, the exchange coupling strength as well as the magnetization orientations of FePt and [CoNi]5 are determined. Meanwhile, it is found the magnetic damping constant α can be modulated considerably as well by adjusting the interlayer thickness. For the Ta interlayer, the α value decreases gradually with the increase in tTa as the result of decreased coupling strength, while it shows a monotonic increasing behavior for the Pt layer. The increased α with tPt can be attributed to the enhanced spin pumping contribution from Pt, which greatly exceeds the decreasing tendency caused by the reduced interfacial coupling. This study provides deep insights into the dynamic behaviors of the exchange-coupled magnetic system, which are valuable to achieve effective control of the ultrafast magnetization dynamics for spintronic applications.

Determination of interface layer effects on magnetic properties of nanocomposite magnets and exchange coupling between magnetic entities

The interlayer plays a crucial role in improving the properties of many extremely important magnetic materials and devices by regulating the magnetic exchange coupling, while it is still not fully understood in a quantitative way. The main obstacle is that there is still no effective way to characterize quantitatively the ferromagnetic exchange coupling (FEC) strength after inserting the interlayer. In this paper, a rationally designed hard/interlayer/soft layered film is used to study the interlayer effects. It is demonstrated that the magnetic properties of nanocomposite magnets can be effectively enhanced through the modification of interface. Here a new concept, using the nucleation field Hns of soft phase as a “detector” to directly and quantitatively characterize/measure the FEC strength across interface and interlayer, is put forward. It is applied to address the dependence of FEC strength on thickness of nonmagnetic Cr and rare earth-rich phase interlayers. The detailed, distinguishing and typical decay behavior and length of FEC strength for these interlayers are successfully resolved for the first time. The new conception and experimental results get also strongly supported by the theoretical calculation. The nature or mechanism of exchange coupling between ferromagnetic grains or layers after adding the nonmagnetic interlayer is identified by using the hard/interlayer/soft layered film as a model system. Our results demonstrate the validity for characterizing/measuring quantitatively the FEC strength across different interlayer materials via strategy established in this work. It opens up new perspectives to gain insight into the interlayer property, and mechanism comprehension and high-performance design for magnetic materials and devices, such as permanent magnets, high-density magnetic recording media, advanced spin-orbit torque devices, etc.

Interfacial Engineering of Ferromagnetism in Epitaxial Manganite/Ruthenate Superlattices via Interlayer Chemical Doping.

Interfacial charge transfer and structural proximity effects are the two essential routes to trigger and tune numerous functionalities of perovskite oxide heterostructures. However, the cooperation and competition of these two interfacial effects in one epitaxial system have not been fully understood. Herein, we fabricate a series of La0.67Ca0.33MnO3/CaRuO3 superlattices and introduce various chemical doping in the nonmagnetic CaRuO3 interlayers. We found that Ti, Sr, and La doping in the CaRuO3 layer can effectively tune the interfacial charge transfer and octahedral rotation, thus modulating the ferromagnetism of the superlattices. Specifically, the B-site Ti doping depletes the Ru 4d band and suppresses the interfacial charge transfer, leading to a decay of ferromagnetic Curie temperature ( TC). In contrast, the A-site Sr doping maintains a sizable charge transfer and meanwhile suppresses the octahedral rotation, which facilitates ferromagnetism and significantly enhances the TC up to 291 K. The La doping turns out to localize the itinerant electrons in the CaRuO3 layer, which suppresses both the interfacial charge transfer and ferromagnetism. The observed intriguing interfacial engineering of magnetism would pave a new way to understand the collective effects of interfacial charge transfer and structural proximity on the physical properties of oxide heterostructures.

Influence of the Conditions of Excitation and Generation of Magnetoelastic Acoustic Emission Signals in Ferromagnetic Materials

We study the influence of the amplitude of induction of the remagnetization field, the thickness of nonmagnetic interlayers between the attached electromagnets and the surfaces of platelike ferromagnetic specimens (made of nickel and St.3 steel), and their thickness on the parameters of magnetoelastic acoustic emission signals. We experimentally confirm the influence of these factors on the shape of envelope curves and the sum of the amplitudes of magnetoelastic acoustic emission signals. It is shown that the time of generation of magnetoelastic acoustic emission signals decreases as the amplitude of induction of the field increases and increases with the thicknesses of the nonmagnetic interlayer and the specimens.

Optimizing Dual-Layer Recording Using Antiferromagnetic Exchange Coupling

Optimizing Dual-Layer Recording Using Antiferromagnetic Exchange Coupling

Monte Carlo simulation of equilibrium and dynamic phase transition properties of an Ising bilayer

Magnetic properties of an Ising bilayer system defined on a honeycomb lattice with non-magnetic interlayers which interact via an indirect exchange coupling have been investigated by Monte Carlo simulation technique. Equilibrium properties of the system exhibit ferrimagnetism with $P$-, $N$- and $Q$- type behaviors. Compensation phenomenon suddenly disappears with decreasing strength of indirect ferrimagnetic interlayer exchange coupling. Qualitative properties are in a good agreement with those obtained by effective field theory. In order to investigate the stochastic dynamics of kinetic Ising bilayer, we have introduced two different types of dynamic magnetic fields, namely a square wave, and a sinusoidally oscillating magnetic field form. For both field types, compensation point and critical temperature decrease with increasing amplitude and field period. Dynamic ferromagnetic region in the presence of square wave magnetic field is narrower than that obtained for sinusoidally oscillating magnetic field when the amplitude and the field period are the same for each type of dynamic magnetic fields.