Magnetic Hysteresis Loops Research Articles

Управление микромагнитной структурой многофазных тонких пленок CoPt путем варьирования толщин слоев

The magnetic properties and micromagnetic structure of [Co/Pt]10 multilayer magnetic films formed by independent variation of the Co and Pt layer thicknesses have been studied. The possibility of the film magnetization parameters manipulation was shown. It is found that the micromagnetic structure of the layers is significantly modified with a change in the thickness of the layers which correlates with the magnetization data. In particular, magnetic force microscopy revealed a system of magnetic skyrmions for a number of structures. The skyrmion density was found to be dependent on the growth conditions which in turn correlates with the shape of the magnetic hysteresis loop. Changing the thickness of the Co and Pt layers makes it possible to control the density of skyrmions in the range from 0.2 to 10.5 µm-2.

Manipulating the Micromagnetic Structure of Multiphase CoPt Thin Films by Varying Layer Thicknesses

The magnetic properties and micromagnetic structure of [Co/Pt]10 multilayer magnetic films formed by independent variation of the Co and Pt layer thicknesses have been studied. The possibility of the film magnetization parameters manipulation was shown. It is found that the micromagnetic structure of the layers is significantly modified with a change in the thickness of the layers which correlates with the magnetization data. In particular, magnetic force microscopy revealed a system of magnetic skyrmions for a number of structures. The skyrmion density was found to be dependent on the growth conditions which in turn correlates with the shape of the magnetic hysteresis loop. Changing the thickness of the Co and Pt layers makes it possible to control the density of skyrmions in the range from 0.2 to 10.5 mkm-2. Keywords: micromagnetic structure, skyrmions, CoPt films, electron beam evaporation.

Comparative study of Nd3+, Cr3+-doped Mg-Zn nanoferrites

The present manuscript portrays, the structural, magnetic, and electrical properties of pristine, Neodymium (Nd3+), and Chromium (Cr3+) doped Mg-Zn nanoparticles [Mg0.9 Zn0.1MxFe2-xO4 NPs, where M = 0, Nd3+, and Cr3+] synthesized by autocombustion method. Structural characterization revealed face-centred cubic crystallinity of all the compositions with space group Fd3¯m. Even though Nd and Cr are members of the rare earth and transition metal families, the differences in their ionic radii cause variations in structural properties of Mg-Mn. The dielectric properties showed that AC conductivity increases with increasing frequency for all the compositions but was maximum for Nd3+ doped sample as compared to pristine and Cr3+ doped Mg-Zn nanoparticles. Magnetic hysteresis loop displayed superparagmagnetic behavior with negligible coercivity and retentivity but the value of saturation magnetization was maximum for Nd3+ doped Mg-Mn nanoparticles, and started decreasing with introduction of Cr3+ ions in the host Mg-Mn ferrites lattice framework, depicting improved magnetic properties due to doping of rare earth ions as compared to transition metal ion substitution. Changes in crystallite size of the host Mg-Zn crystal network, by doping rare earth ions as compared to transition metal ion induces an increment in electrical conductivity, and magnetic properties.

Анизотропия и медленная релаксация аномального эффекта Холла в синтетических ферримагнетиках GdFeCo/Ir/GdFeCo

In synthetic ferrimagnets with perpendicular anisotropy GdFeCo/Ir/GdFeCo, the dependence of the hysteresis loops of the anomalous Hall resistance and the characteristics of the loops on the angle between the magnetic field and the plane of the sample are analyzed. The part of the anomalous Hall resistance corresponding to the spin-orbit torque has been identified. The field dependences of the resistance are sensitive to switching between the magnetic states of the two-layer ferrimagnet and they reproduce the shapes of the magnetization hysteresis loops, calculated with the interlayer exchange interaction, crystal anisotropy, and Zeeman energies at different angles between the field and sample. A slow (~30 min) magnetic relaxation of resistivity hysteresis after reorientation of the sample in magnetic field was found. Specific domain dynamics inherent in two-layer samples was revealed by Kerr microscopy. It was found that slow restoration of the resistivity hysteresis loop is due to domain propagation.

Влияние фрактальности никелевой наносети на ее магнитные свойства

The magnetic properties of a nanonetwork consisting of ultrathin Ni nanowires (diameter < 4 nm) and Ni nanoballs (diameter < 20 nm) are studied at different stages of its growth during laser ablation in a superfluid helium medium. It has been established that, at the early stages of ablation, the nanonetwork consists mainly of nanowires and has a rectangular magnetic hysteresis loop. At the late stages of ablation, the concentration of nanoballs and their diameter increase, and the shape of the hysteresis loop deviates from a rectangular one. The fractal dimension of the nanonetwork is determined, which varies from 1 in the early stages of ablation, when individual nanowires occur, to 2, when the nanonetwork becomes so dense that it is a continuous film. It is shown that the saturation magnetization changes with a change in the fractality of the nanonetwork, which, under constant ablation conditions, is explained by the transformation of nanowires into nanoballs during their folding.

Obtaining and analyzing magnetic hysteresis loops: an insertion of students in magnetism research

Um aparato experimental para a obtenção de curvas de histerese magnética foi construído, com a participação de estudantes de licenciatura em física, visando uma visualização dos fundamentos que caracterizam a resposta magnética de materiais ferromagnéticos submetidos a campos magnéticos alternados. Foram obtidos laços de histereses do núcleo secundário de um transformador, visualizando-os na tela de um osciloscópio na forma gráfica de tensão em um capacitor conectado ao enrolamento secundário em função da tensão medida em um resistor conectado ao enrolamento primário. Os laços foram obtidos para cinco valores de tensão aplicadas ao primário do transformador na faixa de 160–220 V. Foi observado um aumento nos campos coercivo, remanente e magnetização máxima com o aumento da tensão no primário. As curvas de permeabilidade magnética relativa apresentam um máximo próximo aos valores de campo coercivo, e assim observou-se a não linearidade da permeabilidade com o campo intensidade magnética. Por fim, com o aumento da tensão, os estudantes estimaram a potência perdida em 5 curvas de histerese associadas a rotação de dipolos magnéticos e fatores dinâmicos.

Three new MnII-[MoIII(CN)7]4- molecular magnets constructed from chiral bidentate chelating ligands.

Three new cyanide-bridged compounds {[Mn((S,S)-Dpen)]3[Mn((S,S)-Dpen)(H2O)][Mo(CN)7]2·4H2O·4C2H3N}n (1-SS), {[Mn((R,R)-Dpen)]3[Mn((R,R)-Dpen)(H2O)][Mo(CN)7]2·4.5H2O·4C2H3N}n (1-RR), and {[Mn(Chxn)][Mn(Chxn)(H2O)0.8][Mo(CN)7]·H2O·4C2H3N}n (2) (SS/RR-Dpen = (S,S)/(R,R)-1,2-diphenylethylenediamine and Chxn = 1,2-cyclohexanediamine) have been successfully synthesized from the self-assembly reaction of the [MoIII(CN)7]4- unit, the MnII ions, and two chiral bidentate chelating ligands. Single-crystal structure determinations show that compounds 1-SS and 1-RR containing ligands SS/RR-Dpen are enantiomers and crystallize in the chiral space group P21. On the other hand, compound 2 crystallizes in the achiral centrosymmetric space group P1̄ due to the racemization of the SS/RR-Chxn ligands during the growth of the crystals. Despite their different space groups and ligands, all three compounds exhibit similar framework structures consisting of cyano-bridged MnII-MoIII two-dimensional layers separated by the bidentate ligands. The circular dichroism (CD) spectra have further demonstrated the enantiopure character of compounds 1-SS and 1-RR. Magnetic measurements revealed that all three compounds display ferrimagnetic ordering with similar critical temperatures of about 40 K. The chiral enantiomers 1-SS and 1-RR exhibit the magnetic hysteresis loop with a coercive field of about 8000 Oe at 2 K, which is by far the highest for all known MnII-[MoIII(CN)7]4- magnets. Analyses of their structures and magnetic properties indicated that their magnetic properties depend on the anisotropic magnetic interactions between the MnII and MoIII centers, which are closely related to the C-N-M bond angles.

Zero-field-cooling exchange bias up to room temperature in the strained kagome antiferromagnet Mn3.1Sn0.9.

Zero-field-cooling exchange bias (ZFC EB) has always been a research hotspot for researchers, because it can realize the movement of the magnetization hysteresis loop along the field axis without field cooling, which greatly expands the universality and convenience of the application of the exchange bias effect. Achieving ZFC EB at room temperature is an ongoing challenge. To this end, a design strategy from the sublattice level is proposed, and a wide temperature range ZFC EB up to room temperature with a vertical magnetization shift is observed in the strained kagome antiferromagnet Mn3.1Sn0.9. Magnetic analysis and first-principles calculations reveal that the ZFC EB arises from the strong exchange interaction between the non-coplanar antiferromagnetic Mn kagome sublattice occupying normal Mn sites and the collinear ferromagnetic Mn sublattice occupying Sn sites. This discovery is of great significance for the application of ZFC EB in antiferromagnetic spintronic devices.

Magnetic evaluation of accelerated aging degradation on 2.25Cr-1Mo steel with martensitic and bainitic microstructure

Accelerated aging-induced microstructure, mechanical properties, and magnetic properties were evaluated on martensitic and bainitic 2.25Cr-1Mo steel to correlate the properties for magnetic non-destructive evaluation (NDE) of aged Cr-Mo steel components. Decline in hardness and coercive force was observed with the increase in aging time for the microstructural modifications as the pinning of dislocations and magnetic domain wall corresponds to the mechanical and magnetic hardening. Although high hardness and coercive force was found for the martensitic steel compared to the bainitic steel due to its metastable microstructure with large amount of compressive residual stress, in longer periods of ageing the hardness and coercive force was found to be lower for the martensitic steel for its faster degradation. Strong correlations were found among the coercive force and microhardness in both the martensitic and bainitic steels, indicating a possibility of precise NDE of ageing degradation in Cr-Mo steel components by magnetic hysteresis loop measurement through a portable magnetic NDE device.

Probing strongly exchange coupled magnetic behaviors in soft/hard Ni/CoFe2O4 core/shell nanoparticles.

Exchange coupling in a model core-shell system is demonstrated as a step on the path to 3d exchange spring magnets. Employing a model system of Ni@CoFe2O4, high quality core-shell nanoparticles were fabricated using a simple two-step method. The microstructural quality was validated using TEM, confirming a well-defined interface between the core and the shell. A strongly temperature dependent two-phase magnetic hysteresis loop was measured, wherein an analysis of step heights indicates coupling of roughly 50% between the core and the shell. Element-specific XMCD hysteresis confirms the presence of exchange coupling, suppressing the superparamagnetism of the Ni core at room temperature, and reaching a coercivity of >6 kOe at 80 K. These results provide a pathway to the development of heterostructured metal-oxide exchange coupled nanoparticles with improved maximum energy product.

Структура и магнитные свойства порошков сплавов (Sm,Zr)(Co,Fe,Cu)z для магнитопластов

The hard magnetic (Sm,Zr)(Co,Fe,Cu)z alloys intended for the application as powder filler in bonded magnets are considered. The microstructure and intrinsic coercive force of the Sm0.87Zr0.13(Co0.702Cu0.088Fe0.210)6.7, Sm0.81Zr0.19(Co0.702Cu0.088Fe0.210)6.3, and Sm0.85Zr0.15(Co0.690Cu0.070Fe0.240)6.8 alloys, the structural and magnetic states of which were prepared at different aging temperatures and cooling rates, are studied. The formation of the high coercive force and adequate squareness of the magnetic hysteresis loop for alloy powders under study was observed at grain and subgrain sizes of the 2:17 phase of 10 – 20 μm. It is shown that the anisotropic powders of the Sm0.87Zr0.13(Co0.702Cu0.088Fe0.210)6,7 alloy can be prepared for manufacturing bonded magnets with a coercive force of 14 – 20 kOe and higher, which are intended for the application in electric machines.

Magnetic evaluation of accelerated aging degradation on 2.25Cr-1Mo steel with martensitic and bainitic microstructure

Accelerated aging-induced microstructure, mechanical properties, and magnetic properties were evaluated on martensitic and bainitic 2.25Cr-1Mo steel to correlate the properties for magnetic non-destructive evaluation (NDE) of aged Cr-Mo steel components. Decline in hardness and coercive force was observed with the increase in aging time for the microstructural modifications as the pinning of dislocations and magnetic domain wall corresponds to the mechanical and magnetic hardening. Although high hardness and coercive force was found for the martensitic steel compared to the bainitic steel due to its metastable microstructure with large amount of compressive residual stress, in longer periods of ageing the hardness and coercive force was found to be lower for the martensitic steel for its faster degradation. Strong correlations were found among the coercive force and microhardness in both the martensitic and bainitic steels, indicating a possibility of precise NDE of ageing degradation in Cr-Mo steel components by magnetic hysteresis loop measurement through a portable magnetic NDE device.

Влияние радиационного воздействия на магнитные свойства пленок ферромагнетик/IrMn с обменным сдвигом

In this work, the effect of the action of gamma quanta and neutrons on the magnetic properties of Ta/feromagnet/IrMn/Ta bilayer films with an exchange bias of the hysteresis loop is studied. The samples were fabricated by magnetron sputtering, and their structure was studied by small-angle X-ray reflectometry and X-ray diffractometry. The measurement of the magnetic hysteresis loops of the irradiated and non-irradiated samples was carried out by the methods of magneto-optical Kerr magnetometry. As a result, the effect of broadening of the magnetic hysteresis loop after irradiation was found. The maximum broadening of the hysteresis loop was observed in the NiFe/IrMn film under neutron irradiation; in this case, the loop width increased by more than 2.5 times. No noticeable change in the field of the exchange bias of the hysteresis loops was observed in the entire range of radiation exposure.

Strong-coupling superconductivity and weak vortex pinning in Ta-doped CsV3Sb5 single crystals

By measuring magnetizations of pristine and Ta-doped ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ single crystals, we have carried out systematic studies on the lower critical field, critical current density, and equilibrium magnetization of this kagome system. The lower critical field has been investigated in the two typical samples, and the temperature-dependent lower critical field obtained in Ta-doped sample can be fitted by using the model with two $s$-wave superconducting gaps yielding the larger gap of $2{\mathrm{\ensuremath{\Delta}}}_{s1}/{k}_{\mathrm{B}}{T}_{\mathrm{c}}=7.9\phantom{\rule{0.28em}{0ex}}(\ifmmode\pm\else\textpm\fi{}1.8)$. This indicates a strong-coupling feature of the V-based superconductors. The measured magnetization hysteresis loops allow us to calculate the critical current density, which shows a very weak bulk vortex pinning. The magnetization hysteresis loops measured in these two kinds of samples can be well described by a recently proposed generalized phenomenological model, which leads to the determination of many fundamental parameters for these superconductors. Our systematic results and detailed analysis conclude that this V-based kagome system has features of strong-coupling superconductivity, relatively large Ginzburg-Landau parameter, and weak vortex coupling.

Up-Conversion Luminescence and Magnetic Properties of Multifunctional Er3+/Yb3+-Doped SiO2-GdF3/LiGdF4 Glass Ceramics

Glassy nanocomposites containing Yb3+/Er3+-doped GdF3 and LiGdF4 nanocrystals have been prepared by controlled crystallization of the xerogel and the structural, up-conversion luminescence, and magnetic properties were analyzed and discussed. Structural and morphological analysis showed uniform distribution of both GdF3 and LiGdF4 nanocrystals (tens of nm size), embedded in silica glass matrix as the result of thermal decomposition of the trifluoracetates, revealed as a strong exothermic peak at about 300 °C; the Li-ions co-doping showed a strong influence on the GdF3 and LiGdF4 nanocrystalline fraction. The energy dispersive spectrometry mapping showed Gd, F and Yb, Er within the nanocrystals but not in the silica glass matrix. X-ray diffraction pattern analysis indicated the crystalline lattice distortion consistent with the Yb/Er incorporation in both fluoride nanocrystals. The “green” ((2H11/2, 4S3/2) →4I15/2) and “red” (4F9/2→4I15/2) up-conversion luminescences at 525, 545, and 660 nm observed under 980 nm laser light pumping were assigned to the Er3+ ions deexcitation through a two-photon process. The magnetic properties of the nanocomposite are strongly temperature dependent. The magnetization hysteresis loops show a ferromagnetic behavior at low temperatures (5K) related to the rare-earth ions contribution and the saturation magnetization of 39 emu/g. At 300 K a paramagnetic behavior was observed that was ascribed to the non-interacting localized nature of the magnetic moment of the rare-earth ions. Hence, such novel, multifunctional magnetic and optical materials can allow the intertwining between magnetism and photonics and might offer new opportunities for new magneto-optical device development.

Study of the corrosion properties of structural steels using magnetic characteristics

Heterogeneities of the crystal structure and chemical composition, as well as the impurity elements forming inclusions cause deviations of the properties of test object from the required physical and mechanical parameters which significantly affects the reliability and service life of the product. We present the results of studying the susceptibility of structural steels to corrosion in aggressive environment using their magnetic characteristics. Structural-phase transformations occurred in steels under the effect of heat treatment change their properties, including magnetic and corrosion ones. Heat-treated 09G2S, St3, 15XSND steel samples were studied. In addition to the main magnetic parameter — coercive force, we also used spectral characteristics of the samples obtained using a remagnetization curve, magnetic hysteresis loop. The multi-parameter approach with harmonic components was used to identify the corrosion rate and coercive force correlation. Determination of the corrosion rate in this case can be reduced to classical problems of technical diagnostics. It is shown that a complex parameter based on harmonic components obtained using a magnetic hysteresis loop and the corrosion rate exhibit a pronounced correlation which provide developing a non-destructive method for predicting the corrosion resistance of structural steels. The results obtained can be used to improve the rapid method for determining the corrosion-hazardous zones of steels using the magnetic parameters.

The Magnetic Properties and Magnetocaloric Effect of Pr0.7Sr0.3MnO3 Thin Film Grown on SrTiO3 Substrate

The magnetic behaviors and magnetocaloric effect (MCE) of Pr0.7Sr0.3MnO3 (PSMO-7) film grown on a (001) SrTiO3 single-crystal substrate by a pulsed laser deposition (PLD) were studied in this paper. X-ray diffraction with a high resolution (HRXRD) measurement shows that PSMO-7 film is grown with a (001) single orientation. The magnetic properties and the MCE related to the ferromagnetic (FM) phase transition of the PSMO-7 film are investigated using the temperature dependence of magnetization M(T) and the magnetic field dependence of magnetization M(H). The M(T) data suggest that with decreasing temperatures, the PSMO-7 film goes through the transition from the paramagnetic (PM) state to the FM state at around the Curie temperature (TC). The TC (about 193 K) can be obtained by the linear fit of the Curie law. Magnetic hysteresis loop measurements show that the PSMO-7 film exhibits the FM feature at temperatures of 10, 100, and 150 K (low magnetic hysteresis can be found), while the film reveals the PM feature with the temperature increased up to 200 and/or 300 K. The research results of M(H) data are consistent with the M(T) data. Furthermore, the magnetic entropy change (-ΔSM) of the PSMO-7 film was studied. It was found that the maximum value of (-ΔSM) near TC reaches about 4.7 J/kg·K under the applied field change of 20 kOe, which is comparable to that of metal Gd (-ΔSM of 2.8 J/kg K under 10 kOe), indicating the potential applications of PSMO-7 film in the field of magnetic refrigeration.

Magnetic studies of dysprosium and indium doped Co2Z hexaferrites

Dysprosium and Indium doped Co2Z hexaferrite Ba3Co2InyDyxFe23.9-xO41 (where x = 0.0, 0.05, 0.1, 0.15, 0.2 and y = 0.1) were fabricated by sol–gel auto-combustion method. The structural studies were done by XRD and TEM which confirms that prepared samples have a pure Z-type phase. The magnetic studies were done by Vibrating Sample Magnetometer and Mossbauer Spectroscopy. The magnetic hysteresis loop of these samples gives us the value of saturation magnetization, coercive field, and remanence magnetization, from these values we found that Ba3Co2In0.1Dy0.2Fe23.7O41 has the highest saturation magnetization value of 89.065 emu/g. Mossbauer spectra fitted with six sextets of six sites least square fitting gives us information about the presence of Fe3+ state in the sample and that there is no deformation in lattice sites by doping with Dysprosium and Indium dopants as magnetic field vary slightly.

Enhanced magnetic and ferroelectric properties of La[formula omitted]M[formula omitted]FeO[formula omitted] (M = Dy and Y) nanoparticles: A comparison of A-site doping

The room temperature magnetic hysteresis (M-H) loops reveal ferromagnetic-like behavior in an antiferromagnetically ordered LaFeO3 (LFO) material system synthesized by the sol–gel method. The maximum magnetization (Mmax) for the undoped sample annealed at 800 °C is 1.08 emu/g, whereas, with the same annealing, materials that are Dy and Y doped (25%) exhibit four times higher magnetization. It is interesting to note that non-magnetic ion Y3+ doped LFO has the same magnetization as magnetic ion Dy3+ doped nanomaterials. Reduction of particle and crystallite size plays a significant role in enhancing the net magnetization of doped materials. While the magnetization in Y-doped materials is attributed to the anti-symmetric exchange interaction (AEI) through spin canting, the greater magnetization for Dy doped samples is related to the AEI as well as inherent magnetic moment of the Dy3+ ion. The quantified tilting angle (Fe–O–Fe) is higher and the bond length (Fe–O) is smaller for Y-doped compounds compared to Dy-doped samples. X-ray photoelectron spectroscopy for oxygen 1s spectra shows that the relative area of O1− is higher in Dy-doped LFO than Y-doped sample. Ferroelectric hysteresis loops exhibit spontaneous electric polarization with reduced leakage current for Y-doped LFO, while other compounds show leaky behavior.

Exchange bias and interface-related effects in two-dimensional van der Waals magnetic heterostructures: Open questions and perspectives

The exchange bias (EB) effect is known as a fundamentally and technologically important magnetic property of a magnetic bilayer film. It is manifested as a horizontal shift in a magnetic hysteresis loop of a film subject to cooling in the presence of a magnetic field. The EB effect in van der Waals (vdW) heterostructures offers a novel approach for tuning the magnetic properties of the newly discovered single-layer magnets, as well as adds a new impetus to magnetic vdW heterostructures. Indeed, intriguing EB effects have recently been reported in a variety of low-dimensional vdW magnetic systems ranging from a weakly interlayer-coupled vdW magnet (e.g., Fe3GeTe2) to a bilayer composed of two different magnetic vdW materials (e.g., Fe3GeTe2/CrCl3, Fe3GeTe2/FePS3, Fe3GeTe2/MnPS3, Fe3GeTe2/CrSe, Fe3GeTe2/CrOCl, Fe3GeTe2/CoPc, Fe5GeTe2/FePS3), to bilayers of two different vdW defective magnets (e.g., VSe2/MoS2), or to metallic ferromagnet/vdW defective magnet interfaces (e.g., Fe/MoS2). Despite their huge potential in spintronic device applications, the physical origins of the observed EB effects have remained elusive to researchers. We present here a critical review of the EB effect and associated phenomena such as magnetic proximity (MP) in various vdW heterostructure systems and propose approaches to addressing some of the emerging fundamental questions.