Transformation Of Magnetic Structure Research Articles

Bending annealing induced transformation of magnetic structure in Co-rich amorphous microwires

For the first time, the magnetic structure of a glass-coated microwire, previously subjected to bending annealing was investigated. Magnetic and magneto-optical analyses were performed after the sample was annealed and returned to a straightened state. Changes in the magnetic structure, induced by the bending annealing, were observed both within the microwire and on its surface. The spatial distribution of the magnetic structure was primarily attributed to the spatial distribution of the stress gradient resulting from bending stress. Special emphasis was placed on the transformation of surface domain structures, with the diversity of these structures indicating a significant influence of bending-annealing-unbending procedure on their formation process.

Orbital Hybridization Induced by Double‐Anion Coordination to Enhance Room‐Temperature Ferromagnetic Response

The oxygen introduction is expected to enable manipulation of material properties, however, the coordination mechanism between oxygen and other nonmetal dopants remains inadequate. Herein, the oxygen introduction into cobalt selenides has been achieved through annealing in a controlled gas environment to disclose the anion defects formation process. Superconducting quantum interference device (SQUID) measurements indicate that the cobalt selenides annealed exhibit significantly enhanced room‐temperature ferromagnetism. Calculations reveal that the magnetic improvement is mainly attributed to orbital hybridization induced by double‐anion coordination (selenium and oxygen). This work can provide new insight into the role of oxygen incorporation in magnetic structure transformation.

Reversible and Non-Reversible Transformation of Magnetic Structure in Amorphous Microwires

We provide an overview of the tools directed to reversible and irreversible transformations of the magnetic structure of glass-covered microwires. The irreversible tools are the selection of the chemical composition, geometric ratio, and the stress-annealing. For reversible tuning we use the combination of magnetic fields and mechanical stresses. The studies were focused on the giant magnetoimpedance effect and the velocity of the domain walls propagation important for the technological applications. The essential increase of the giant magnetoimpedance effect and the control of the domain wall velocity were achieved as a result of the use of two types of control tools. The performed simulations reflect the real transformation of the helical domain structures experimentally found.

Light‐Controlled Ferromagnetism in Porphyrin Functionalized Ultrathin FeS Nanosheets

AbstractThe intrinsically weak photomagnetic interaction makes it difficult to realize effectively light‐controlled magnetic structure transformation. Here unprecedented light‐induced switching of magnetism is reported in porphyrin functionalized ultrathin FeS nanosheets. Contrary to the antiferromagnetic (AFM) bulk, the troilite FeS nanosheets demonstrate a ferromagnetic (FM) behavior due to superficial symmetry breaking. Under light irradiation, a large number of photo‐generated carriers take part in a singlet‐to‐triplet conversion through intersystem crossing of tetra(4‐carboxyphenyle)porphyrin molecules decorated on the nanosheets. The generated triplet carriers make spin flips occur at FeS surface, finally leading to a magnetic structure transition from FM to AFM configuration. The findings not only shed new light on steering arrangement of spin electrons but also open up almost unlimited possibilities for spintronics and optical detection of spin‐dependent physiological reactions.

Antiferromagnetic states of BiFeO3 single crystal multiferroic in external magnetic field

Room-temperature multiferroics take special attention due to possibilities for applications in technology, but they are also interesting from fundamental point of view. Bismuth ferrite is the most studied multiferroic demonstrating high ordering temperatures and fascinating properties in thin films and could be used as a functional element in magnetoelectric memory. For better utilization of bismuth ferrite in spintronic devices the detailed understanding of its properties is of great importance. In this work we apply the developed thermodynamic model for description of magnetic states and magnetic field driven transformation of magnetic structure of single crystal BiFeO3. Presence of magnetic field may lead to a situation, when the transition from inhomogeneous magnetic state having cycloidal structure into homogeneous state proceeds through emergence of intermediate magnetic state with conical-like structure. Magnetic field transitions emerging under influence of magnetic field should somehow lead to alternation of magnetization. For revealing this influence the magnetization curves were calculated for three directions of magnetic field and the comparison with experimental results was carried out. Good agreement with experimental curves allows us to say, that peculiarities of magnetization curves may be caused by the emergence of intermediate conical state.

Large topological Hall effect in a geometrically frustrated kagome magnet Fe3Sn2

We report on the observation of a large topological Hall effect (THE) over a wide temperature region in a geometrically frustrated Fe3Sn2 magnet with a kagome-bilayer structure. We found that the magnitude of the THE resistivity increases with temperature and reaches −0.875 μΩ cm at 380 K. Moreover, the critical magnetic fields with the change of THE are consistent with the magnetic structure transformation, which indicates that the real-space fictitious magnetic field is proportional to the formation of magnetic skyrmions in Fe3Sn2. The results strongly suggest that the large THE originates from the topological magnetic spin textures and may open up further research opportunities in exploring emergent phenomena in kagome materials.

Exotic phases of frustrated antiferromagnet LiCu2O2

7Li NMR spectra were measured in a magnetic field up to 17 T at temperatures 5-30 K on single crystalline LiCu2O2. Earlier reported anomalies on magnetization curves correspond to magnetic field values where we observe changes of the NMR spectral shape. For the interpretation of the field and temperature evolutions of our NMR spectra, the magnetic structures were analyzed in the frame of the phenomenological theoretical approach of the Dzyaloshinskii-Landau theory. A set of possible planar and collinear structures was obtained. Most of these structures have an unusual configuration; they are characterized by a two-component order parameter and their magnetic moments vary harmonically not only in direction, but also in size. From the modeling of the observed spectra, a possible scenario of magnetic structure transformations is obtained.

Transformation of magnetic structure in amorphous microwires induced by temperature and high frequency magnetic field

The study of the magnetic properties of glass-covered amorphous microwires is reported. This study is focused on the influence of a high frequency electric current and of temperature upon the surface magnetic domain structure. Investigations are performed using the magneto-optical Kerr effect technique, and it is found that the high frequency current and heating process have a great and essential influence upon the surface magnetization reversal and surface domain structure. The induced formation and transformation of the surface magnetic structure are key processes that determine the stable operation of giant magneto-impedance devices.

Giant magnetoresistance and field-induced magnetic phase transitions in Gd7Rh3 studied on single crystals

Magnetization measurements in steady and pulsed fields and magnetoresistance measurements in different field-current geometries on single crystalline samples have been employed to study the field-induced magnetic phase transitions in the antiferromagnetically (AF) ordered compound Gd7Rh3 with hexagonal crystal structure of the Th7Fe3 type. Below TN=141K, the magnetic structure transformations from AF to the forced ferromagnetic (FF) state, which are accompanied by a giant reduction of the electrical resistivity (up to 7 times at low temperatures), were observed under the magnetic fields along the c-axis and in the basal plane. This giant magnetoresistance is associated with magnetic superzone effects. The negative temperature coefficient of the electrical resistivity and a large magnetoresistance were also observed in the paramagnetic region in Gd7Rh3; which are suggested to result from the retention of short-range AF correlations in a wide temperature range above TN.

Giant magnetoresistance and field-induced phase transitions in Tb7Rh3 single crystal

High-field magnetization and magnetoresistance measurements have been performed to investigate the field-induced magnetic phase transitions in Tb7Rh3 single crystals. Metamagnetic transitions were observed along the a-, b- and c-axes of the hexagonal crystal lattice in the three magnetic states at temperatures below the Neel temperature TN = 91 K; magnetic field H — temperature T phase diagrams were constructed for b- and c-axes. At temperatures below TN, the magnetic structure transformations under application of a magnetic field along the b-axis are observed to be accompanied by the giant magnetoresistance effect (|Δρ/ρ| up to 65%). Magnetization curves measured at temperatures above TN show inflection points, which may be indicative of phase transitions within regions with an antiferromagnetic short-range order persisting in a paramagnetic matrix.

Edge and Shape Dependence of the Magnetization Reversal of Patterned Exchange-Biased Bilayers

The magnetization reversal processes in an exchange-coupled nanocomposite system, consisting of a continuous film of the ferromagnet Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">77</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> Mo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> with a square mesh of the antiferromagnet FeMn on top, as a function of an external magnetic field were investigated by the magneto-optical indicator film technique. It was found that the boundary conditions near the antiferromagnetic (AFM) stripes crucially influence the remagnetization kinetics in the ferromagnetic film. Unusual behavior was revealed for different topologically stable structures at 180 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> domain walls in the ferromagnetic film. Also, the magnetization reversal of the ferromagnetic regions underneath the antiferromagnetic stripes is different for applied fields parallel and perpendicular to the sample's unidirectional anisotropy. In both cases, an asymmetry in the magnetic structure transformation during remagnetization of the AFM-covered parts of the ferromagnetic film was observed for the forward and backward branches of the hysteresis loop.

Magnetic and microwave absorption properties of electrospun Co0.5Ni0.5Fe2O4 nanofibers

Co0.5Ni0.5Fe2O4 nanofibers with 70–100nm in diameter were fabricated by the electrospinning and calcination process. Their saturation magnetization gradually enhances from 37.5 to 66.2emu/g with increasing calcination temperature from 450 to 800°C, while the corresponding coercivity increases initially, achieving a maximum value of 78.3kA/m at 600°C and then decreases with further increase in calcination temperature due to the transformation of magnetic structure from single-domain to multi-domain. By dispersing the nanofibers into a silicon rubber matrix homogeneously, the electromagnetic parameters of them were measured in the frequency range of 2–18GHz and the microwave reflection loss was calculated according to the transmission line theory. The reflection loss exceeding −5dB is obtained between 11 and 18GHz for the silicon rubber composites containing 15vol% Co0.5Ni0.5Fe2O4 nanofibers with coating thicknesses of 2.5–3.2mm. These Co0.5Ni0.5Fe2O4 nanofibers possess a good microwave absorption performance in the Ku band and have a great potential as microwave absorber for practical applications.

Effect of the transformation of the magnetic structure of a FeBO3:Mg crystal on its magnetooptical anisotropy

The field dependence of the magnetic linear birefringence (MLB) in easy-plane weak FeBO3:Mg ferromagnet has been investigated. It is found that MLB nonmonotonically (stepwise) tends to a constant value with an increase in magnetic field at low temperatures. This feature of MLB in FeBO3:Mg is related to the transformation of the crystal magnetic structure during magnetization.

Induced magnetic phase transitions in GdCo/Co-type multilayer films

The magnetic structure transformation of the layered ferrimagnet [Co/Gd36Co64]4/Co in an external magnetic field was comprehensively studied. Using magnetometrical, magnetooptical, and magnetoresistive techniques, it is established that, when magnetized in fields exceeding a threshold value H cr, the collinear magnetic structure formed by the magnetic moments of the Co and GdCo layers is distorted. The value H cr varies nonmonotonically with temperature T and reaches a minimum at the temperature of magnetic compensation of the layered ferrimagnet. The H cr(T) dependence is well described in terms of the homogeneous ferrimagnet model with an adequately chosen phenomenological intersublattice interaction constant taking into account the weakened coupling of the surface Co layers with the internal part of the actual layer structure.

Transformation of the magnetic structure of FeBO3 under high pressures

The transformation of magnetic structure under hydrostatic and quasi-hydrostatic pressures up to 4 GPa was studied for iron borate FeBO3 by the neutron diffraction method. Under quasi-hydrostatic conditions, the orientation of iron magnetic moments changes at pressures P≥1.4 GPa. Under hydrostatic conditions, no changes in the magnetic structure of iron borate were observed up to 2.1 GPa. This behavior is caused by the influence of the inhomogeneity (in magnitude and direction) of elastic stresses on the configuration of magnetic sublattices.

Mesoscopic magnetism and the phenomenon of exchange anisotropy: MBE grown Cu(1 1 0)/Ni 80Fe 20/Fe 50Mn 50 bilayers with corrugated interfaces

A comprehensive analysis of the giant in-plane uniaxial magnetic anisotropy of exchange biased molecular beam epitaxy grown Cu(1 1 0)/Ni 80Fe 20/Fe 50Mn 50 bilayers, discovered by Jungblut et al. (J. Appl. Phys. 75 (1994) 6659) is presented. Cu(1 1 0)/Ni 80Fe 20 samples have a uniaxial in-plane volume anisotropy with a [0 0 1] easy axis direction. Covering such ferromagnetic (F) layers with an antiferromagnetic (AF) Fe 50Mn 50 layer introduces an interface contribution to the uniaxial anisotropy that leads to an [1 1 ̄ 0] easy axis direction for F layer thicknesses below a critical value of 4 nm, and to an enhancement of the [0 0 1] anisotropy for larger thicknesses. The effect occurs only for Fe 50Mn 50 layers that are thicker than the minimum thickness that is required to obtain the exchange bias effect. From in situ low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) the Ni 80Fe 20 surface is shown to be corrugated, viz. in the form of elongated 2–4 monolayer high mesas at a distance of typically 4–8 nm in the [0 0 1] direction and a length along the [1 1 ̄ 0] direction of 25–60 nm. We show that this novel mesoscopic magnetic effect can be explained from the magnetically uncompensated nature of the AF (1 1 0) surface in combination with the corrugation of the F/AF interface. The spatially varying sign of the F–AF exchange coupling then leads to a preferred F layer magnetization direction that is perpendicular to the staggered AF magnetization. The remarkable change of sign of the interface anisotropy indicates that in the thin and thick F layer regimes the staggered AF magnetizations that are frozen in during the growth are different by a 90° rotation. We tentatively explain this from the kinetics of magnetic structure transformations in the bilayer during the growth process. The local exchange bias interaction parameter obtained from a quantitative analysis is J eb,loc ≈2.5–10 mJ/m 2 , which is close to the theoretical upper limit and is two orders of magnitude larger than the sample averaged interaction parameter, J eb, obtained from the exchange bias field. This provides the first direct experimental proof that the observed value of J eb of an AF/F bilayer can be the result of much larger but almost completely averaged out opposing local AF–F exchange interactions. The paper contains a brief overview of the recent developments in the field of mesoscopic magnetism.

Magnetic interactions and phase transitions in the Co- and Ni-doped manganites

A magnetic study of perovskites R(Mn1−xBx)O3 (R Eu, Gd, Tb, Dy, Y; B Ni, Co) is reported. It is found that investigated perovskites are nonhomogeneous ferromagnets with relatively high Curie temperatures. The magnetic anisotropy of Ni-containing perovskites is much lower than that of Co-containing ones. It is supposed that domains with different charge states of ions and magnetic structure coexist in a wide range of Co- and Mn-concentrations. The applications of the magnetic field leads to the transformation of magnetic structure. Evidence is presented for an antiferromagnetic rare-earth - manganese magnetic interaction.

Magnetic Properties of Gadolinium Silicide Thin Films for Different Heat Treatments

ABSTRACTThe magnetic properties of heavy rare earth silicide GdSi2-x thin films are investigated as a function of the annealing temperature of the films. Resistivity measurements reveal in the two films annealed at high and low temperatures, but for a short time, the existence of two transition temperatures corresponding to the presence of an ordered and a disordered structure. In the film annealed at high temperature for a long time, only one transition temperature occurs. It corresponds to a magnetic structure transformation.

Magnetic phase transitions in erbium

Magnetic properties of a high-purity single crystal of erbium have been investigated in magnetic fields of Oe and kOe ranges and temperature region from 4.2 to 300 K. Considerable temperature hystereses of erbium magnetization were found near each of the magnetic phase transition points Θ 1, Θ 2 and Θ B. The data obtained are used for the analysis of magnetic structure transformations in erbium.

Magnetic structure transformation in MnPt

A magnetic structure transformation has been observed in MnPt. On increasing the temperature the magnetic moments turn from the tetragonal axis to the basal plane. In Mn 0.9Pt 1.1 between 5°K and T M the magnetic moments lie in the basal plane.