N. A. Usov

Measurement of weak magnetic field of corrosion current of isolated corrosion center

A very small magnetic field of corrosion current, of the order of 10−4 Oe, generated by isolated zinc inclusion in a copper platelet placed in electrolyte has been measured for the first time with a highly sensitive giant magneto-impedance magnetometer. The total corrosion current of the inclusion is estimated comparing the measured magnetic field distribution with corresponding theoretical calculation. The estimated value of the total corrosion current turns out to be in reasonable agreement with that one obtained in the standard gravimetric measurement.

Universal behavior of dense clusters of magnetic nanoparticles

A detailed numerical simulation of quasistatic hysteresis loops of dense clusters of interacting magnetic nanoparticles is carried out. Both clusters of magnetically soft and magnetically hard nanoparticles are considered. The clusters are characterized by an average particle diameter D, the cluster radius Rc, the particle saturation magnetization Ms, and the uniaxial anisotropy constant K. The number of particles in the cluster varies between Np = 30 - 120. The particle centers are randomly distributed within the cluster, their easy anisotropy axes being randomly oriented. It is shown that a dilute assembly of identical random clusters of magnetic nanoparticles can be characterized by two dimensionless parameters: 1) the relative strength of magneto-dipole interaction, K/Ms2, and the average particle concentration within the cluster, η = V Np/Vc. Here V is the nanoparticle volume, and Vc is the volume of the cluster, respectively. In the strong interaction limit, Msη/Hau2009 > > u20091, where Ha = 2K/Ms is the a...

Magnetic properties of polycrystalline cobalt nanoparticles

The energy diagram of stationary magnetization states existing in polycrystalline cobalt nanoparticles in the range of diameters 20 ≤ D ≤ 60 nm has been calculated by means of numerical simulation. It is shown that in polycrystalline cobalt nanoparticles in the range of diameters D ≥ 32 nm only vortex states with low average magnetization are present, whereas mostly quasi-uniform states are realized in nanoparticles with diameter D ≤ 24 nm. Thus, the effective single-domain diameter of polycrystalline cobalt nanoparticles is estimated to be Dc = 24 nm. It is approximately two times smaller than the actual single-domain diameter of monocrystalline cobalt nanoparticle, Dc0 = 45 nm. The hysteresis loops of a dilute assembly of polycrystalline cobalt nanoparticles in the range of diameters D ≤ Dc are characterized by a coercive force that is approximately 2.5 times less compared with that of the randomly oriented assembly of monocrystalline cobalt nanoparticles.

A high-sensitivity scanning magnetometer based on the giant magneto-impedance effect for measuring local magnetic fields of corrosion currents

The design, main characteristics, and specific features of a new high-sensitivity magnetometer based on the giant magneto-impedance (GMI) effect in amorphous ferromagnetic microwires are considered. It is shown that, in addition to measuring homogeneous fields, the device is capable of detecting weak local magnetic fields of conduction currents and ion currents involved in corrosion processes. Results of in situ magnetic measurements of corrosion processes in the model system of copper–zinc in a sulfuric acid solution qualitatively agree with the data of direct corrosion tests employing the standard gravimetric method.

Soliton collisions in soft magnetic nanotube with uniaxial anisotropy

The structure of stable magnetic solitons of various orders in soft magnetic nanotube with uniaxial magnetic anisotropy has been studied using numerical simulation. Solitons of even order are immobile in axially applied magnetic field. Odd solitons show decreased mobility with respect to that of head-to head domain wall. Solitons of various orders can participate in nanotube magnetization reversal process. Various coalescence and decomposition processes in soliton assembly are considered. It is shown that the general magnetization state of magnetic nanotube consists of chains of magnetic solitons of various orders.