Surface Magnetization Reversal Research Articles

Temperature Dependence of Magnetization Dynamics in Co/IrMn and Co/FeMn Exchange Biased Structures

Thin film ferromagnet/antiferromagnet (F/AF) exchange biased structures that are widely used in GMR spin valves are considered nowadays as promising systems for antiferromagnetic spintronic and spin-orbitronic devices. Here, the temperature dependences of magnetization dynamics in Co/IrMn and Co/FeMn F/AF structures are investigated using ferromagnetic resonance (FMR) in comparison to a free Co layer. A strong additional decrease in the resonance field was observed in Co/IrMn with a temperature decrease attributed to the rotatable anisotropy increase, which almost vanished at room temperature. In contrast to Co/IrMn, the contribution of the rotatable anisotropy in Co/FeMn is much weaker, even though it exists at RT, it is negative, and slightly varies with the temperature and resonance field shift in Co/FeMn. This is mainly due to unidirectional exchange anisotropy. FMR linewidth for the free Co layer increases with decreasing temperature and is accompanied with a slow relaxation process, while the additional contribution to FMR line broadening in Co/IrMn and Co/FeMn structures is correlated with variation in the exchange anisotropy. The observed results are discussed based on structural and surface morphology and magnetization reversal characterization using X-ray diffraction, atomic force microscopy, and vibrating sample magnetometry data.

Surface Crystallization and Magnetization Reversal Processes in Amorphous Microwires

Surface Crystallization and Magnetization Reversal Processes in Amorphous Microwires

Surface Magnetization Reversal of Wiegand Wire Measured by the Magneto-Optical Kerr Effect.

The Wiegand wire is known to exhibit a unique feature of fast magnetization reversal in the magnetically soft region accompanied by a large Barkhausen jump. We clarified a significant difference between the magnetization reversals at the surface and at the entire cross section of a Wiegand wire. We conducted magnetization measurements based on the magneto-optical Kerr effect and applied conventional methods to determine the magnetization curves. The switching field of the magnetization reversal at the surface was greater than that at the initiation of a large Barkhausen jump. Our analysis suggests that the outer surface layer exhibits low coercivity.

Ultrafast Spin Dynamics of Electrochemically Grown Heusler Alloy Films

The electrochemical growth of Heusler alloy film with good morphological quality and crystalline order using single-crystalline substrate is demonstrated. Static magneto optical Kerr effect studies are employed to reveal the surface magnetization reversal of the films. An understanding of the intrinsic nature of the magnetization dynamics in this class of electrochemically grown materials is presented using time-resolved magneto optical Kerr effect measurements, under femtosecond laser excitation. Excitation laser fluence dependence study reveals the ultrafast demagnetization time, fast remagnetization time, and magnetic damping parameter as well as their correlation. © 2021 American Chemical Society. All rights reserved.

Electrodeposited Heusler alloy films with enhanced magneto-optical property

Growth of Heusler alloy films through techniques other than conventional physical vapor deposition presents a challenge for spintronic materials research. In this study an electrochemical deposition approach for these alloys is demonstrated in which sub-micron thickness control can be achieved. By using magneto optic Kerr effect and Kerr microscopy measurements a systematic study of surface magnetization reversal behavior of these films is presented. The results demonstrate that the growth of sub-micron films of Co2FeSn leads to significant enhancement in magneto optic Kerr rotation. A large Kerr rotation value up to 300 mdeg was observed for thin films of thickness ∼200 nm. The modified scheme reported here opens up a path for exploration of electrochemical method as a facile route for fabricating Heusler alloys with improved surface property.

Surface magnetic structures induced by mechanical stresses in Co-rich microwires

We report the results of both magneto-optical Kerr effect and magnetometry studies of torsion stress induced transformation of the surface domain structure and magnetization reversal process in amorphous microwires. The coexistence of different types of domain structures depends on amplitude and sign of the torsion stress. The obtained results were analyzed using model supposing the existence of surface domains of different types in inner core – outer shell of microwires. The experimentally determined volume contribution to magnetization reversal is comparable with the volume contribution obtained as a result of simulation.

Multidomain Structures in Magnetic Microwire

Because of the importance of the surface magnetic properties for the optimal operation of magnetic sensors based on giant magneto-impedance effect (GMI), for the last few years we have studied the surface magnetization reversal and surface domain structure of glass-coated microwires using the magneto-optical Kerr effect (MOKE) technique [1]. Taking into account that the Curie temperature of Co-based microwires lies in the temperature range of approximately 100–450°C (depending on chemical composition), the surface magnetic structure should experience great transformation in a temperature range higher than room temperature. Moreover internal stresses induced by glass coating are the characteristic feature of glass-coated microwires [2]. Obviously the strength of internal stresses depends on temperature. Therefore now we direct our efforts to a new area of the investigation that is very important for the stable operation of magnetic sensors that use microwires as active elements — the influence of changing temperature on the surface magnetic structure.

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.

Experimental demonstration of basic mechanisms of magnetization reversal in magnetic microwires

We report on the magneto-optical study of surface magnetization reversal in glass covered Co-rich microwires. Four different mechanisms of magnetization reversal were found to exist, depending on external magnetic field configuration. An analysis of the results obtained was performed using the theoretical model which proposes the existence of four magnetization states with different chirality. This model was developed previously to describe current-induced switching in wires with variable inner core radius. The co-existence of stable and meta-stable helical magnetic states on the microwire surface is the basic reason for the variety of mechanisms observed for the magnetization reversal.

Magnetic properties of sub-micrometric Fe-rich wires

The investigation of the magnetization reversal has been performed in Fe-rich sub-micrometric glass covered wires of different radiuses. The surface magnetization reversal has been studied using the magneto-optical Kerr effect. The axial tensile stress and torsion stress have been applied during the experiments.Surface hysteresis loop was found to be rectangular because of magnetic bistability. This confirms the existence of the Surface Large Barkhausen Jump in sub-micrometric glass covered wires explained by the magnetization reversal in a large single surface domain.The analysis of the tensile and torsion stresses' transformation of surface hysteresis loop proves that magnetic bistability earlier observed in thicker glass covered microwires exists down to one order decrease of wire's diameter.

High-Frequency Electric Current Influence on Magnetization Reversal and Domain Structure in Co-Rich Amorphous Microwires

We report investigations on influence of high-frequency electric current on surface magnetization reversal and surface domains nucleation in amorphous glass covered microwires. Magneto-optical Kerr magnetometry and microscopy have been used. A strong change of surface magnetization reversal and the transformation of the surface domain structure induced by electric current within a frequency range of 100 Hz-15 MHz have been found.

Nucleation and transformation of circular magnetic‐domain structure in amorphous microwires

AbstractWe report investigations on surface magnetic‐domain structure in amorphous glass‐covered microwires using polar and longitudinal Kerr microscopy. For the first time the main stages of the surface magnetization reversal has been discovered: domain‐wall motion related to the formation of stable circular monodomain and the following multiplication of the number of domains that finishes in the formation of the reversed circularly magnetized state.

Surface magnetization reversal and magnetic domain structure in amorphous microwires

AbstractThis paper presents a review on magneto‐optical investigations of the glass‐coated amorphous microwires including magneto‐optical magnetometry and microscopy. We also discuss a Kerr‐effect method of domain‐wall‐motion detection in glass‐coated wires within a classical Sixtus–Tonks experimental scheme. The developed techniques make it possible to observe the surface magnetization reversal and to establish the main mechanisms of domain‐structure formation and transformation.

Magnetization reversal in thin glass covered amorphous microwires with helical anisotropy

The surface magnetization reversal has been studied in Co-rich amorphous glass-covered microwires. The studies have been performed by the magneto-optical Kerr effect surface loop tracer for the series of the microwires with diameters of 16.8–5.8 μm. The experiments have been carried out in the crossed axial and circular magnetic fields. The variety of the magnetic behaviour has been found in dependence on the diameter of the microwire, that confirms the existence of the helical domain structure in the Co-rich microwires. The special behaviour has been discovered for the wire with the diameter of 10 μm. From this results we can conclude that the axially magnetized inner core disappears for this value of the microwire diameter and that the domain structure of the microwire consists only of the helical domain structure. The experiments are in good agreement with calculations based on the model taking into account the existence of the helical anisotropy in the surface area of the microwires.

Kerr Microscopy Study of Magnetic Domain Structure Changes in Amorphous Microwires

In this paper, we report investigations on circular magnetic domain structure in amorphous microwires. Polar magneto-optical Kerr microscopy was used for the observation of the magnetic domains images. The surface magnetization reversal is determined basically by the circular domains nucleation. For the first time, the rearrangement of the surface domain structure is observed as a part of the magnetization reversal process in amorphous microwires.

Experimental Determination of Relation Between Helical Anisotropy and Torsion Stress in Amorphous Magnetic Microwires

Surface magnetization reversal of Co-rich amorphous glass covered microwires in the presence of torsion stress has been studied by magneto-optical Kerr effect. The dependence of the angle of the helical anisotropy on the applied torsion stress has been obtained for the first time based on the analysis of the magneto-optical experimental results. The value of the limit angle of the torsion stress induced helical anisotropy has been found.

Relation between surface magnetization reversal and magnetoimpedance in Co-rich amorphous microwires

We report the investigations on the giant magnetoimpedance (GMI) effect and the surface magnetic structure performed in the series of glass covered Co-rich amorphous microwires with different thicknesses of glass covering. The calculation of the surface hysteresis loops has been performed in the frames of the model which takes into account the helical magnetic anisotropy. The correlation between the value of the GMI ratio, the jump of the circular magnetization, and the value of the angle of helical anisotropy has been established. It was found that the angle of the surface helical anisotropy, for which the highest value of GMI, is close to 60°.

Magneto-optical determination of helical magnetic structure in amorphous microwires

Surface magnetization reversal has been investigated in Co-rich glass-covered microwires. Difference in mechanism of the surface magnetization reversal has been observed in the microwires with different thicknesses of glass covering. Correlation of the surface magnetic properties and the surface helical magnetic anisotropy has been found.

Investigation of surface magnetization reversal in Co-rich amorphous microwires with magneto-impedance effect

Investigation of the surface magnetization reversal and the magnetoimpedance (MI) effect have been performed in Co-rich glass-covered microwires with identical composition and different thickness of glass covering. The correlation between the mechanism of the surface magnetization reversal and the value of MI effect has been discovered. The Kerr effect study showed that the bias magnetic field induces shift of circular hysteresis loop. This shift could be considered as a characteristic feature of the high value of the MI ratio.

Study of surface magnetic properties in Co-rich amorphous microwires

Magneto-optical investigations carried out on a Co-rich glass-covered amorphous microwire is presented. The appearance of circular magnetic bistability and the influence of tensile stress and high-frequency electric current on the surface magnetization reversal have been studied. The change of the mechanism of the magnetization reversal induced by the high-frequency electric current is also discussed.