E. I. Kunitsyna

Magnetic noise as the cause of the spontaneous magnetization reversal of RE–TM–B permanent magnets

The relation between the macroscopic spontaneous magnetization reversal (magnetic viscosity) of (NdDySm)(FeCo)B alloys and the spectral characteristics of magnetic noise, which is caused by the random microscopic processes of thermally activated domain wall motion in a potential landscape with uniformly distributed potential barrier heights, is found.

Anomalous effect of Sm additives on the magnetic properties of (Nd1-xSmxDy)(FeCo)B intermetallics

Contributions of the “soft” (Nd1-xSmxDy)2(FeCo)2B and “hard” (Nd1-xSmxDy)2(FeCo)14B magnetic phases to the temperature and field dependences of magnetization and low-frequency magnetic susceptibility of (Nd1-xSmxDy)(FeCo)B alloys have been separated. It is established that a small increase in the concentration of Sm within 0.8–3 at % leads to significant variations in the exchange integrals and magnetic anisotropy field of the alloy.

Effect of samarium impurity on the relaxation of the magnetization of a (NdDy)(FeCo)B alloy

Small Sm additions (~1–3 at %) have been found to slow down the relaxation of the magnetization in a magnetic field in the (NdDy)(FeCo)B alloy by several times. The effective “freezing” of the spontaneous relaxation of the magnetic moment is related to the substantial increase in the potential barriers for motion of domain walls when introducing Sm ions that have other symmetry of the single-ion anisotropy than that of Nd and Dy ions. The results can be used to stabilize the properties of hard magnets.

Magnetic properties of CoFeB alloys doped with Dy and Pr

Powders of the ferrimagnetic alloy CoFeBDyPr have been synthesized by the gas atomization method. Annealing of the samples at 900°C leads to the recrystallization of the amorphous phase into the crystalline phase (Pr,Dy)2Fe7Co7B, which changes the magnetic properties of the alloy (the coercive force decreases, the shape of the magnetic hysteresis loop changes, etc.). The temperature dependences of the remanent magnetization and Mössbauer spectra depend on the size of particles. This indicates the contribution from subsurface magnetic states of the phase of different chemical composition, which is identified by X-ray photoelectron spectroscopy in particles with sizes of less than 10 μm. A weakening of the dipole-dipole interaction between particles in the sample, where they are diluted in the solid organic matrix (eicosane), leads to a change in the shape of the hysteresis loop. The elimination of the mechanical mobility of particles in eicosane significantly increases (to 2.5 times) the coercive force.

Effect of stoichiometry of Fe and Co on the temperature stability of the magnetic anisotropy in Pr-Dy-Fe-Co-B alloys

An increase in the cobalt concentration in Pr-Dy-Fe-Co-B alloys leads to the substitution of Co atoms for Fe atoms in the atomic positions, which are the nearest neighbors with the rare-earth metal atoms, and to the formation of a significant number of boron-rich phases. At the highest (limiting) cobalt concentrations, boron can be substituted for the transition metals. As a result, the exchange interaction between magnetic sublattices of the rare-earth and transition metals is weakened. In turn, this leads to a decrease in the contribution from the rare-earth ions to the magnetic anisotropy, the temperature stability of which increases.

Magnetic properties and spin dynamics of CoFeB–SiO2 multilayer granular heterostructures

It has been found that CoFeB–SiO2/C and CoFeB–SiO2/Bi2Te3 multilayer heterostructures with a cluster structure of CoFeB layers feature a long-range magnetic order in the entire temperature range from 2 to 300 K. At high temperatures (T = 300 K), CoFeB clusters exhibit magnetic properties characteristic of superparamagnets. At low temperatures (T = 5 K), clusters are ferromagnetic, and the easy magnetization axis is in the film plane. The temperature of the ferromagnetic-to-superparamagnetic state transition of clusters depends on a dielectric interlayer material: the use of Bi2Te3 instead of C as a spacer layer leads to an increase in the transition temperature by a factor of 4 and an increase in the magnetization blocking temperature of CoFeB clusters in a field of 100 Oe by a factor of 3.

Increase in the coercivity of an ensemble of (DyPr)–(CoFe)–B microparticles during their dispersion in a polymer matrix

In ensembles of annealed ferrimagnetic alloy (DyPr)–(CoFe)–B microparticles in the free state and fixed in polymer, the coercivity differs more than by an order of magnitude. The contributions of orientation locking of magnetic axes of particles and the dipole magnetic interaction between particles to the coercivity and saturation magnetization field of an ensemble are discussed. In ensembles of unannealed microparticles, the effect of their locking and dispersing in polymer is significantly weaker.

Women in Physics in Russia—Changes from 2002 to 2005

Access to education regardless of gender with availability of child-care facilities and legal protection of working mothers produced a considerable proportion of highly qualified women during the many years of the Soviet period of Russian history. Women were active in most public spheres, including science. After the collapse of the Soviet Union in 1991, all scientists were faced with shortage of funding and very low salaries. Even now, in 2005, the average monthly salary in research institutes of the Russian Academy of Sciences (RAS) is about

Dependence of the coercive force on the magnetic field sweep rate in (PrDy)(FeCo)B alloys

200 USD, which is only slightly more than the minimum living standard. The circumstances of the transitional period have put women scientists, including physicists, in a much more difficult situation than men, because of our county’s lack of social welfare policies, together with traditionally rigid patterns of promotion and recognition. The married woman has become the second bread-winner, and low salaries require many women scientists to take second or even third

Effect of copper concentration on atomic site occupation by Fe ions and magnetic properties of (PrDy)–(FeCo)–B alloys

The dependence between the coercive force and the average hysteresis loop record time was revealed in sintered (Pr1 – xDyx)13(Fe1 – yCoy)79B8 magnets. The coercive force was established to grow by 22% with an increase in the average hysteresis loop sweep rate within a range of 1.1 × 102–3 × 105 Oe/min, obeying a logarithmic dependence on the loop passage velocity with saturation at low rates. Some domain structure transformations produced by a magnetic field in the process of magnetization were established by magnetic force microscopy.