Ferromagnetic Resonance Studies Research Articles

Effect of Thermal Processing on the Structural and Magnetic Properties of Epitaxial Co2FeGe Films.

The structure and magnetic properties of epitaxial Heusler alloy films (Co2FeGe) deposited on MgO (100) substrates were investigated. Films of 60 nm thickness were prepared by magnetron co-sputtering at different substrate temperatures (TS), and those deposited at room temperature were later annealed at various temperatures (Ta). X-ray diffraction confirmed (001) [110] Co2FeGe || (001) [100] MgO epitaxial growth. A slight tetragonal distortion of the film cubic structure was found in all samples due to the tensile stress induced by the mismatch of the lattice parameters between Co2FeGe and the substrate. Improved quality of epitaxy and the formation of an atomically ordered L21 structure were observed for films processed at elevated temperatures. The values of magnetization increased with increasing TS and Ta. Ferromagnetic resonance (FMR) studies revealed 45° in-plane rotation of the easy anisotropy axis direction depending on the degree of the tetragonal distortion. The film annealed at Ta = 573 K possesses the minimal FMR linewidth and magnetic damping, while both these parameters increase for another TS and Ta. Overall, this study underscores the crucial role of thermal treatment in optimizing the magnetic properties of Co2FeGe films for potential spintronic and magnonic applications.

Growth, magnetic, and electronic properties of Ni-Zn ferrites thin films

Abstract Thin films of Ni-Zn ferrite grown on MgO(111) single crystal substrate were prepared using radiofrequency magnetron sputtering, with a target of nominal composition Ni0.5Zn0.5Fe2O4. Subsequently, x-ray diffraction (XRD) was performed, which revealed characteristic reflections of a Ni-Zn ferrite structure, confirming the unique formation of the ferrite. X-ray photoelectron spectroscopy (XPS) revealed the presence of metal ions in their appropriate valence states within the crystalline structure of the Ni-Zn ferrite. The variation in binding energy observed in the thin film is attributed to changes in the environment of Fe3+ and Zn2+ or Ni2+ ions, resulting from the non-equilibrium distribution of cations in tetrahedral and octahedral sites. The saturation magnetization and the coercivity field were 7.05 μ B / cell and 513 ± 32 Oe, respectively. In addition, ferromagnetic resonance studies were made using broad-band FMR spectroscopy based on a coplanar waveguide (CPW) spectrometer.

Disclosing magnetic clusters in the metallic half-Heusler ferromagnet Cr4PtGa17 with a breathing pyrochlore lattice

We report a ferromagnetic resonance (FMR) study of a single crystal of Cr4PtGa17, the first material of a half-Heusler (HH) type with a metallic ferromagnetic breathing pyrochlore structure. The spatial distribution of the magnetic free energy density derived from the FMR data appears to be of a cubic symmetry despite the lower symmetry coordination of magnetic Cr ions. This surprising finding strongly suggests that the Cr4Ga14 structural unit at the Y site of the HH general XYZ formula forms an octahedrally shaped integral magnetic cluster, likely due to strong exchange interaction between the Cr ions via covalent Cr-Ga-Cr bonds. The presence of magnetic clusters within a regular metallic lattice appears to be a new intriguing characteristics of these novel types of HH compounds whereas Cr4PtGa17, at the same time, constitutes the rare example of such metallic pyrochlore-type material.

Interfacial reaction behavior between ferromagnetic CoFeB and the topological insulator Sb2Te3

The successful prevention of interfacial reactions between ferromagnetic materials and topological insulators (TIs) is crucial for the realization of reliable spintronic devices using TIs. To this end, we investigated the magnetic properties and interfacial reaction behavior of a bilayer structure composed of ferromagnetic CoFeB and TI Sb2Te3. The effects of including a MgO interlayer was also investigated. Ferromagnetic resonance (FMR) studies showed a remarkably weak resonance peak for the sample annealed at 400 °C for the 2-nm-thick interlayer, and finally, no resonance peak for a film below 1 nm in thickness was observed. X-ray diffraction (XRD) results demonstrated that the Sb2Te3 peak intensities started to decrease upon annealing at 200 °C and completely disappeared for annealing temperatures >400 °C. Hard X-ray photoelectron spectroscopy (HAXPES) results also support that the core-level peaks of Sb and Te split upon annealing at temperatures >200 °C, suggesting the dissociation of Sb2Te3. These results indicate that Sb2Te3 and CoFeB react at the interface during annealing, resulting in a loss of the ferromagnetic properties of the CoFeB layer. Meanwhile, a sample containing a 3-nm-thick MgO layer retained its original Sb2Te3/MgO/CoFeB structure even after annealing at 400 °C, as evidenced by its unchanged XRD peak intensity and FMR spectrum. We expect that our findings will be highly valuable in developing TI-based spintronic devices.

Dual mode spin to charge conversion using inverse spin Hall effect in NiFe/FeMn/NiFe multilayer thin films

Microwave devices with more than one operating frequency and their ease of tunability are of great importance for high-frequency information processing. Magnetic thin films offer an unparalleled advantage of engineering different microwave bands that can be precisely tailored and reconfigured externally. Here, novel trilayer structures consisting of NiFe/FeMn/NiFe with varying antiferromagnetic FeMn layer thickness have been investigated by exploring their ferromagnetic resonance (FMR) properties and inverse spin Hall effect (ISHE) responses. Two-step magnetic hysteresis loops are observed for higher FeMn thickness (t ⩾ 12 nm), where the bottom NiFe layer shows a comparatively more significant shift due to the presence of strong interfacial exchange coupling. FMR study reveals two resonant modes associated with the two ferromagnetic layers, which are distinguishable for higher thicknesses of FeMn or at high excitation frequencies. The choice of FeMn thickness determines the operating frequencies, which can be finely tailored by optimizing the FeMn thickness. Gilbert damping parameter is found to be in the range of 0.009–0.012 where the presence of exchange bias adds to the the scattering mechanisms. Prominent ISHE responses are obtained from the bottom NiFe layer as compared to the top NiFe layer. Variation of FeMn thickness also shows a strong influence on the spin pumping ( Vsp ), and perpendicular anisotropic magnetoresistance ( VAMR⊥ ) components. The results are correlated with the efficiency of spin flow and spin-to-charge conversion of the FeMn layer. Our systems can be used as an emerging alternative for microwave detectors and microwave energy harvesters.

Charge-ordering breakdown dynamics and ferromagnetic resonance studies of B-site Cu diluted Pr1‒x Sr x MnO3

Here, we report the influence of Jahn–Teller active Cu substitution on the charge-ordering (CO) characteristics of one of the well-known manganite Pr0.45Sr0.55MnO3 (S55) with a distorted tetragonal structure. Magnetization studies unveil a complex magnetic phase diagram for S55, showing distinct temperature ranges corresponding to various magnetic phases: a ferromagnetic phase dominated by the Double Exchange interaction with T C ∼ 220.5 K, an antiferromagnetic phase below T N ∼ 207.6 K induced by CO with a transition temperature of T CO ∼ 210 K consistent with the specific heat C P(T) data, and a mixed phase in the range T N < T < T CO due to the competitive interplay of these two interactions. Dilute substitution of Cu at the Mn B-sites disrupts the robust charge-ordered state, leading to enhanced ferrimagnetic order with T FN ∼273 K and significant magnetocrystalline anisotropy as confirmed by ferromagnetic resonance (FMR) studies. The Cu-substituted system displays a distinct cationic distribution compared to the pristine S55, contributing to its diverse magnetic structure. Our findings also reveal the irreversible metamagnetic transition (H T-Max ∼ 8.85 kOe at 180 K) associated with the CO phenomena in S55 and the first-order nature of the phase transition across T CO. The magnetic heat capacity critical analysis (C Mag = A (T − T N)−α ) yields the exponent, α = 0.097 (0.154) in the region T > T N (T < T N) consistent with the magnetic structure. The temperature dependence of FMR resonance field ΔH Res(T), peak-to-peak width H PP(T), and Gilbert damping factor α G(T) show clear anomalies across the magnetic transitions signifying the important role of admixtured (3+/4+) electronic state of Mn. Additionally, a strong correlation between the FMR α G(T) and switchable magnetic entropy change (ΔS Max ∼ −8/+ 3 J kg−1 K−1 for ΔH = 90 kOe) has also been established in S55.

Microwave heterostructures in the form of submicron Y&lt;sub&gt;3&lt;/sub&gt;Fe&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt; films on non-oriented ferroelectric ceramic substrates: synthesis, properties, and prospects for applications

In the work monolithic structures of yttrium iron garnet (YIG, Y3Fe5O12) with a thickness of about 2 μm were obtained on ferroelectric ceramic substrates based on PbZr0.45Ti0.55O3 (PZT) and Ba0.4Sr0.6TiO3 (BST). The Y3Fe5O12 layer was deposited by ion beam sputtering deposition on substrates 400 μm thick by sputtering a polycrystalline Y3Fe5O12 target with with argon ions. The heterostructures were crystallized by annealing in air at a temperature of 820 °C for 5 min. The results of the characteristic X-ray radiation method showed that the elemental composition of the monolithic heterostructure corresponds to the specified one. During X-ray studies, it was found that the YIG crystallization process is completed and the resulting structure is single-phase. The results of magnetic and ferromagnetic resonance studies indicate the possibility of using the obtained heterostructures in logic circuits based on spin waves with low scattering, in memory elements, as well as in electrically controlled microwave devices.

Enhanced magnetocaloric effect in melt-spun Mn[formula omitted]Fe[formula omitted]Ge3 (x = 0 and 1) ribbons with anisotropy induced spin-dimensionality crossover

We report the structural, magnetic, magnetocaloric and ferromagnetic resonance properties of melt-spun Mn5−xFexGe3 (x = 0 and 1) ribbons. The melt-spun Mn5Ge3 ribbons exhibit hexagonal structure with preferential growth along c-axis while Fe doping retains the structure but changes preferential growth in in-plane direction. Fe doping enhances the ferromagnetic to paramagnetic phase transition temperature of Mn5Ge3 ribbons. Elaborate isothermal magnetization data analyses in the critical region yield critical exponents β= 0.344(1), γ= 1.284(1) and δ= 4.70(1) with critical temperature TC= 303.64(1) K for x = 0 while β= 0.389(1), γ= 1.334(1) and δ= 4.441(1) with TC= 330.84(1) K for x = 1. Further, the magnetization data in the vicinity of TC satisfies the magnetic scaling equations of state characteristic of a second-order phase transition. The magnetocaloric performance is reflected through maximum entropy change −ΔSmmax(T) ∼ 5.0(2.9) J kg−1 K−1; refrigerant capacity RC ∼ 505(302) J kg−1 and temperature-averaged entropy TEC(10 K) ∼ 4.92(2.28) J kg−1 K−1 at an applied field of 5 T for x = 0(1) ribbons, respectively. −ΔSmmax(T) embracing the critical region is found to be well-described by the critical exponents that are consistent with those determined by the modified Arrott plots and Kouvel–Fisher analyses. Renormalization group calculations further confirm that Mn5Ge3 and Mn4FeGe3 systems behave as 3D Ising and 3D Heisenberg ferromagnets in the critical region wherein short-range extended magnetic interactions decay as J(r) ≈ r−4.995 and r−4.895 with intermoment distance, respectively. Ferromagnetic resonance study reveals that with the introduction of Fe, the magnetocrystaline anisotropy (Ku∼1.4×106 erg/cm3) of Mn5Ge3 gets suppressed so much so that the system exhibits a crossover from 3D Ising to 3D Heisenberg universality class in the critical region.

Microstructure, ferromagnetic resonance, and electrical analysis of Ho-substituted Li-Ni nanoparticles

The substitution of rare earth ions is a novel approach to vary the dynamic magnetic properties of soft ferrites to such an extent that its electrical properties and ferromagnetic resonance (FMR) response can be set over a broad frequency range. In this work, a complete transmission electron microscopy (TEM), scanning electron microscopy (SEM), ferromagnetic resonance spectroscopy (FMR), X-ray photoelectron spectroscopy (XPS), and current-voltage (I-V) analysis of holmium (Ho) substituted lithium-nickel soft ferrites with composition Li1.2Ni0.4Fe2−xHoxO4 (x = 0, 0.03, 0.06, 0.09, 0.12, and 0.15) is carried out. TEM analysis reveals a spherical shape distribution of nanoparticles with a particle size of ∼ 50 nm. FMR study is carried out to check the role of Ho addition on magnetic energy losses, FMR line position, and shape. The shift in FMR line shape is mainly attributed to the anisotropy contribution, relaxation processes, and ferromagnetic interactions between the magnetic nanoparticles. XPS experiments confirm the presence of all compositional elements along their valence states. The Ho substitution increased the electrical resistivity, whereas the damping of A-B exchange interactions resulted in a decline of Curie temperature (Tc), which is required for high-frequency power applications.

Interface Effects on Magnetic Flux Pinning in La0.7Sr0.3MnO3/YBa 2Cu3O7-x Bilayers.

The magnetic pinning properties of a ferromagnet/superconductor hybrid structure consisting of a La0.7Sr0.3MnO3(LSMO) layer with various thicknesses on top of a fixed thickness YBa2Cu3O7-x (YBCO) layer are investigated in this article. The existence of a weakly magnetic layer was identified at the interface between YBCO and LSMO by a ferromagnetic resonance (FMR) study. Magnetic moment and anisotropy of the interfacial layer were probed using the angular-dependent FMR study. This layer gives rise to an additional flux pinning contribution to the bulk magnetic pinning from the LSMO layer. Our study provides insight into the complex interface physics in the LSMO/YBCO bilayer system, promoting a new pathway for the development of novel flux pinning-related functionality.

Cryogenic Temperature Growth of Sn Thin Films on Ferromagnetic Co(0001)

AbstractTopological electronic materials hold great promise for revolutionizing spintronics, owing to their topological protected, spin‐polarized conduction edge or surface state. One of the key bottlenecks for the practical use of common binary and ternary topological insulator materials is the large defect concentration that leads to a high background carrier concentration. Elemental tin in its α‐phase is a room temperature topological semimetal, which is intrinsically less prone to defect‐related shortcomings. Recently, the growth of ultrathin α‐Sn films on ferromagnetic Co surfaces has been achieved; however, thicker films are needed to reach the 3D topological Dirac semimetallic state. Here, the growth of α‐Sn films on Co at cryogenic temperatures was explored. Very low‐temperature growth holds the promise of suppressing undesired phases, alloying across the interfaces, as well as the formation of Sn pillars or hillocks. Nevertheless, the critical Sn layer thickness of ≈3 atomic layers, above which the film partially transforms into the undesired b‐phase, remains the same as for room‐temperature growth. From ferromagnetic resonance studies, and supported by electron microscopy, it can be concluded that for cryogenic Sn layer growth, the interface between Sn and Co remains sharp and the magnetic properties of the Co layer stay intact.

Comprehensive Law‐of‐Approach‐to‐Saturation for the Determination of Magnetic Anisotropy in Soft Magnetic Materials

Magnetocrystalline anisotropy is a crucial parameter that determines the suitability of magnetic material in a wide range of emerging applications. The law‐of‐approach‐to‐saturation (LAS), utilized to obtain the magnetocrystalline anisotropy from hysteresis loops, is not satisfactory for materials with cubic anisotropy as they are two orders higher than the bulk value. Herein, a modified formulation to LAS is presented, where the reduction in effective magnetic anisotropy (K) values due to Fe oxide phases in Fe particles over wide size ranges is accounted. The value ofKdecreases from 4.2 × 104 J m−3for the Fe particles of average size 210 nm to 1.2 × 104 J m−3for the 20 nm particles due to the increase in the iron oxide fraction with size reduction. The effective magnetic anisotropy obtained from the modified LAS has been validated from the ferromagnetic resonance studies for particles of the smallest size.

Manifestations of Spinodal Decomposition into Dilute Pd1-xFex “Phases” in Iron-Implanted Palladium Films: FMR Study

Palladium-iron alloys produced by high-dose implantation of iron ions into epitaxial palladium films were investigated with the ferromagnetic resonance (FMR) and vibrating sample magnetometry (VSM) techniques. The samples reveal distinct multiple FMR responses depending on the dose of iron ion implantation. The post-implantation annealing at 770 K does not bring the implanted films to a homogeneous solid solution state, as might be expected from the Pd-Fe phase diagram. On the contrary, the system approaches a stable state composed of several magnetic phases. FMR spectra exhibit an angular behavior specific for a stack of interacting magnetic layers. This observation, correlated with the magnetometry data, indicates that the palladium-iron binary alloy has a previously unknown tendency towards spinodal decomposition into isostructural phases with well-defined iron concentrations and, accordingly, with different temperatures of ferromagnetic ordering and saturation magnetizations.

Magnetization and spin resonances in helical spin systems

In this work, magnetization and magnetization dynamics in helical-ordered spin systems are considered. By employing the Nelder–Mead simplex numerical algorithm, the dependence of spin orientations on magnetic field is calculated for spin systems with arbitrary helicity. As demonstrated, in a certain case, the dependence of magnetization on magnetic field shows a clear dependence on helicity. Next, magnetization dynamics in helical-ordered spin systems with arbitrary helicity is studied by employing the Suhl–Smit–Beljers approach. Two types of resonance responses are examined: the molecular field response and collective spin resonance modes. Both types of responses also demonstrate clear dependence on helicity. Thus, it is demonstrated that the overall combination of magnetization measurements and ferromagnetic resonance studies defines the helical angle.

Ferromagnetic resonance in exchange-coupled magnetic vortices

The results of a study of low-frequency ferromagnetic resonance in a system of two overlapping permalloy disks by magnetic resonance force spectroscopy are presented. It is shown that the resonant frequency of the gyrotropic mode of oscillations of magnetic vortices in this system significantly depends on the vorticity of their shells. The experimental dependences of the resonant frequencies of various states on the external magnetic field are qualitatively consistent with the results of micromagnetic modeling. Keywords: ferromagnetic resonance, magnetic resonance force spectroscopy, magnetic vortices.

Spin mixing conductance of the iridate/manganite interface

The results of studies of ferromagnetic resonance (FMR) of iridate/manganite epitaxial heterostructures in a wide range of microwave frequencies (1- 20 GHz) are presented. The magnitudes of imaginary and real parts of the spin mixing conductance of the heterostructure boundary determining the spin current were determined from the frequency dependence of the spin damping and changes in the resonance field of the FMR. It is shown that the value of the imaginary part of spin conductance is comparable to the real part, which may be caused by strong spin-orbit interaction occurring in 5d-oxides of transition metals (iridate). Keywords: ferromagnetic resonance, SrIrO3/La0.7Sr0.3MnO3 heterostructures, spin current, spin mixing conductance.

Спиновая проводимость границы иридат/манганит

The results of studies of ferromagnetic resonance (FMR) of iridate/manganite epitaxial heterostructures in a wide range of microwave frequencies (1-20 GHz) are presented. The magnitudes of imaginary and real parts of the spin mixing conductance of the heterostructure boundary determin-ing the spin current were determined from the frequency dependence of the spin damping and changes in the resonance field of the FMR. It is shown that the value of the imaginary part of spin conductance is comparable to the real part, which may be caused by strong spin-orbit interaction present in 5d-oxides of transition metals (iridate).

Magnetism dynamics driven by phase separation in Pr-doped manganite thin films: A ferromagnetic resonance study

We performed ferromagnetic resonance measurements of a ${({\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x})}_{1\ensuremath{-}y}{\mathrm{Ca}}_{y}\mathrm{Mn}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ with $x=0.52\ifmmode\pm\else\textpm\fi{}0.05, y=0.23\ifmmode\pm\else\textpm\fi{}0.04$, and $\ensuremath{\delta}=0.14\ifmmode\pm\else\textpm\fi{}0.10$ thin single crystalline film which, in combination with micromagnetic simulations, reveal three temperature regions consistent with (i) a ferromagnetic-paramagnetic transition in which ferromagnetic domains nucleate and grow, (ii) followed by a filamentary fluidlike percolation of magnetic domains exhibiting dynamic processes and finally, iii) the existence of a blocking temperature below which the magnetism is a metastable glassy-like state with strong decoherence of the uniform resonance mode. Our results suggest a strain-liquid to strain-glass spin order transition in which the magnetism and fluidlike dynamics of the separated phases freeze at low temperatures. We show the magnetism dynamics depend strongly on the phase-separated state and morphology of the magnetic domains suggesting a route to control of phase separation and realization of spintronic and magnonic devices.

Light and microwave driven spin pumping across FeGaB–BiSb interface

3-D topological insulators (TI) with large spin Hall conductivity have emerged as potential candidates for spintronic applications. Here, we report spin to charge conversion in bilayers of amorphous ferromagnet (FM) Fe_{78}Ga_{13}B_{9} (FeGaB) and 3-D TI Bi_{85}Sb_{15} (BiSb) activated by two complementary techniques: spin pumping and ultrafast spin-current injection. DC magnetization measurements establish the soft magnetic character of FeGaB films, which remains unaltered in the heterostructures of FeGaB-BiSb. Broadband ferromagnetic resonance (FMR) studies reveal enhanced damping of precessing magnetization and large value of spin mixing conductance (5.03 x 10^{19} m^{-2}) as the spin angular momentum leaks into the TI layer. Magnetic field controlled bipolar dc voltage generated across the TI layer by inverse spin Hall effect is analyzed to extract the values of spin Hall angle and spin diffusion length of BiSb. The spin pumping parameters derived from the measurements of the femtosecond light-pulse-induced terahertz emission are consistent with the result of FMR. Kubo-Bastin formula and tight-binding model calculations shed light on the thickness-dependent spin-Hall conductivity of the TI films, with predictions that are in remarkable agreement with the experimental data. Our results suggest that room temperature deposited amorphous and polycrystalline heterostructures provide a promising platform for creating novel spin orbit torque devices.

Simulations of FMR for study the shape anisotropy in square hollow nanopillars

A study of ferromagnetic resonance in square hollow nanopillars was carried out, with the aim of analyzing the effects of geometry. Nanopillars (NPs) with L = 120 nm length and D = 30 nm external width were studied. By fitting the data for parallel field and using the Primary peak, the anisotropy field was HA = 97.2, 116.4 and 144.5 kA/m for d = 0, 10 and 20 nm, respectively. For perpendicular field, HA = 175, 193 and 251 kA/m for d = 0, 10 and 20 nm, respectively. The variations were attributed to the increase in dipole interactions, as the cavity size increases. A secondary peak was also fitted and HA = 222.5, 220 and 226.9 kA/m were obtained for parallel configuration. Thus, this secondary peak, from regions whose local field varies little with the dimensions of the cavity, were attributed to the effects of parallel edges.