N.V. Kudrevatykh

Law of approach to saturation in highly anisotropic ferromagnets Application to NdFeB melt-spun ribbons

Abstract The magnetization curves of melt-spun ribbons of NdFeB with ( BH ) max =16 MGOe have been measured in pulsed high magnetic fields up to 400 kOe to examine the applicability of the law of approach to ferromagnetic saturation to highly anisotropic uniaxial ferromagnets. The magnetization in the region M ≥0.95 Ms can be described well with the law of approach to saturation. From the analysis of the magnetization curve, the spontaneous magnetization, effective anisotropy constant and high-field susceptibility are estimated at room temperature. These values are consistent with those evaluated from single-crystalline data of Nd 2 Fe 14 B.

Magnetic properties of TbFe11Ti single crystal

Abstract The magnetization and magnetostriction curves of tetragonal TbFe 11 Ti single crystal along the main crystallographic directions in static magnetic fields up to 7 T and the temperature interval 4.2–340 K have been measured. On the basis of these data, the temperature dependences of the anisotropy constant K 4 4 ( T ), magnetostriction constant λ 2 α ,2 ( T ) and the value of the f-d exchange parameter ξ 0 were determined and compared with theoretical results derived from the single-ion anisotropy mechanism for the Tb sublattice.

Temperature dependence of single-ion anisotropy and magnetostriction coefficients of rare earth ferromagnets in terms of quantum theory

Abstract The quantum methods for calculation of the temperature dependences of single-ion magnetocrystalline anisotropy and magnetostriction coefficients in a wide temperature range are under discussion in this paper. The experimental data on anisotropy of Th single crystal and intermetallic compounds of the R 2 Co 17 type, where RPr, Nd, Sm, are analysed on the basis of quantum theory. A good agreement of the theory with experiment is achieved.

Crystal structure of Er2Fe17 nitride

Abstract The crystal structure of the Er 1.85 Fe 17.3 N 2.58 compound, which belongs to the family of R 2 Fe 17 N 3 -type nitrides has been studied by neutron diffraction. It was found that the structure of this compound should be described as a partially disordered Th 2 Ni 17 -type. Its peculiar feature is a random substitution of Fe-atoms (“dumbbells”) for Er atoms. It leads to a deviation from the precise 2:17 stoichiometry to a more Fe-rich ratio (up to 2:19). Nitrogen atoms in this nitride occupy mainly only one type of interstitial 6h-sites.

Hysteresis properties of nanostructured Nd-Ho-Fe-Co-B alloys

The structure and magnetic properties of a rapidly quenched (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2. alloy are investigated by the X-ray and electron diffraction and by the standard magnetometry techniques. It is found that using the quenching velocity of Vq = 30 m/s, it is possible to attain the high-coercive state (iHc > 20 kOe) at room temperature as a result of formation of nano-sized grains of the main 2-14-1 phase. The low-temperature study of hysteresis properties of the material obtained is performed for the first time.

The Spin-Reorientation Transition in a Nanocrystalline Nd-Ho-Fe-Co-B Alloy and its Influence on the Hysteresis Loops

The temperature dependence of coercivity (Hc) of a nanocrystalline (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 alloy in a wide temperature range, including the spin reorientation (SR) transition interval, has been investigated. A considerable decrease in the Hc for the SR in the range 150–4.2 K was detected and interpreted as being an effect caused by the anisotropy change of the 2-14-1 phase nanograins, i.e., from the uniaxial to the easy-cone type.

High-pressure effect on the magnetization and magneto-crystalline anisotropy in a single crystal of HoFe11Ti

Abstract We have studied the magnetization of a HoFe 11 Ti single crystal under high pressure (up to 10 kbar) and high magnetic fields (up to 5 T) in the temperature range 5–300 K. A decrease of magnetization with pressure (−0.057 μ B /f.u. kbar) was observed in the whole temperature range. A significant increase of the critical field of the first-order magnetization process with pressure was observed at low temperatures (0.065 T/kbar).

Microstructure and Magnetic Hysteresis in Nanocrystalline Nd-Fe-Co-B Alloys on the Base of Nd2Fe14B Phase

Using the electron microscopy (SEM and TEM), X-ray structure analysis and precise magnetometry methods (VSM, SQUID-magnetometer), the microstructure and magnetic hysteresis properties of industrial manufactured hard magnetic rare-earth based alloys of Nd-Fe-Co-B compositions (BZMP and MQP-B brands) that are widely applied as fillers for bonded magnets (magnetoplasts and magnetoelasts) have been studied. The obtained results allow selecting the proper temperature range for bonded magnets applications on the base of BZMP and MQP-B fillers.

Determination of Texture Degree of NdFeB-Magnets by Means of Neutron Diffraction

Six samples of Nd-Fe-B-permanent magnets, distinguished in the texture degree, have been measured by neutron diffraction in the reflection and transmission regimes. The texture in the samples was formed by application of impulses of external magnetic field 0H = 4 T. Analysis of the obtained neutron diagrams by means of the Fullprof program allowed quantitative determination of the texture degree and conclusion to be made that the texture degree grows with an increase in numbers of magnetic field impulses.

Structural state and magnetic properties of Nd2Fe14 B-type rapidly quenched alloys

Using X-ray, elastic neutron diffraction (END) and small angular neutron scattering (SANS) methods (Diffractometers D2 and D3 respectively), transmitting electronic microscopy (JEOL JEM-200CX) and magnetometry technique (vibrating sample magnetometer -VSM) the structure and magnetic properties of the rapidly quenched (RQ) alloys of the following compositions: A) Nd14Fe78B8; B) Y12Fe82B6; C) Nd13.3 Co6.6 Fe72.6Ge0.9B6.6; D)Nd9Fe85B6; E) Nd9Fe79B12; F) Nd9Fe74Ti4C B12 have been studied. At some quenching conditions or after consequent heat treatments of these alloys the nanoscale state of the main 2-14-1 phase and ?-Fe grains can be formed. Their size depends on the sample-preparation conditions and lies in the interval of 10–200 nm. Their influence on magnetic properties of alloys under study is discussed.