The magnetization reversal in ordered arrays of Co nanowires with tailored hcp-phase texture, controlled by pH synthesis and nanowires length, has been investigated. The angular dependence of coercivity has been experimentally determined for different crystal textures, and the corresponding magnetization reversal mode is interpreted by analytical modelling. The results show that reversal takes place by propagation of a transverse-like domain wall mode. The fitting of experimental and calculated data allows us the quantitative evaluation of the magnetocrystalline anisotropy constant strength whose magnetization easy direction evolves from parallel to the wires toward in-plane orientation with the change of hcp-phase texture. The simple geometry and high aspect ratios of arrays of magnetic nanowires make them a model system for the study of magnetic phenomena in uniaxial nanomagnets for modern devices applications.1,2 While ultrasoft magnetic nanowires (i.e., permalloy) have been exhaustively investigated, Co nanowires form a particularly interesting system as it is a hard magnetic material which magnetic properties strongly depend on their crystal structure (i.e., phases, texture, and grain size). The control of the orientation of hcp-c axis (i.e., magnetization easy axis of magnetocristalline anisotropy, K mc ) results in the control of the Co nanowires effective anisotropy. A strong longitudinal magnetic anisotropy is achieved when the c axis is oriented parallel to the nanowires, so reinforcing the shape anisotropy. Since the magnetization reversal process is determined by the strength and orientation of the effective magnetic anisotropy, its detailed control and understanding will benefit advances in those applications.In Co nanowires prepared by electrochemical route, crystalline structure can be tuned by adjusting fabrication parameters as current density, plating time, pH, pore diameter, or annealing and deposition under external magnetic fields.3-7 Particularly, it has been shown that pH-controlled electroplating enables the switching between fcc and hcp-Co phases, which modifies the magnetization easy axis from parallel to perpendicular to the wires. 6,7 This is typically qualitatively concluded from the differences in the hysteresis loops shape between parallel and perpendicular applied magnetic field configurations.To achieve full understanding of the magnetization reversal defined by a given anisotropy, the study of coercivity and, specifically of its angular dependence, is an useful tool. Different reversal modes can be induced by suitable modification of the K mc parameter. This feature is relevant for the design of hybrid systems, as multilayers of different Co crystallographic structures, and consequently different controlled reversal modes, which is of interest in spintronic and microwaves devices. Previous works on Co/Cu multilayer nanowires 8 show that competing anisotropies can be present in nanowires. The control of magnetic anisotropy in these nanostructured systems is very important both fo...

We have studied the domain wall longitudinal propagation and its dynamics under the influence of transverse magnetic field in thin magnetic wires. A different behavior was observed for strong and weak transverse fields. In weak transverse field Ht, the domain wall dynamics depends on the direction of Ht. Transverse field applied in one direction increases the Walker limit and shifts the existence of transverse domain wall to higher axial field. Transverse magnetic field applied in opposite direction decreases the Walker limit and favors vortex domain wall even at low fields. Different behavior was obtained in strong transverse field which speeds up the domain wall velocity to its saturation value of 9 km/s independently on the orientation of transverse field.

To cite this version:P Klein, R Varga, P Vojtanik, J Kovac, J Ziman, et al. They combine advantages of nanocrystalline alloys exhibiting simultaneously increased Curie temperature and magnetic bistability, which is required for modern sensoric and spintronic devices. Positive magnetostriction of the crystalline FeCo grains results in a magnetic bistability, whereas good soft magnetic properties remains stabilized. As a result of mechanical stress induced by the glass-coating, the optimum temperature range for thermal treatment is enhanced up to 600 o C.

We report a ferromagnetic resonance study of biphase magnetic microwires consisting of soft amorphous nucleus, intermediate nonmagnetic layers, and harder outer crystalline shell. Real and imaginary impedance components are investigated under increasing static axial magnetic field with a network analyzer in the microwave frequency range for selected microwires with different soft nuclei. Natural ferromagnetic resonance is even observed for particular microwires with strong axial anisotropy. The presence of a hard phase induces a second absorption peak at frequencies lower than those of the soft phase. Moreover, magnetic anisotropy of different soft phases is deduced from the evolution of resonance frequency with applied field.

Ni–Mn–Ga ferromagnetic shape memory wires (Ni2.10Mn0.98Ga0.92, mean diameter 170 μm) are obtained by the rotating water bath melt spinning technique. The compositional heterogeneity linked to its dendritelike structure gives rise to a complex and broad martensitic transformation (MT). The reduced value of magnetization in the as-spun sample is ascribed to Mn–Mn antiferromagnetic interactions at structural defects as atomic disorder, vacancies, and antiphase boundaries structures. Moreover, the observed low temperature magnetic relaxation process is characterized by a splitting in the zero-field-cooled/field-cooled magnetization curves and the frequency shift in the ac magnetic susceptibility. The results are interpreted in terms of the coexistence of a reduced magnetization state and nearly noninteracting magnetic clusters. A high temperature treatment optimizes both the MT and the magnetic characteristics (i.e., decrease in the hysteresis of the MT and magnetization recovery, respectively).