A.S. Volegov

Magnetic order, field-induced phase transitions and magnetoresistance in the intercalated compound Fe0.5TiS2

Measurements of the magnetic susceptibility, magnetization, electrical resistivity and neutron diffraction have been performed for the compound Fe(0.5)TiS(2) in which Fe atoms are intercalated between S-Ti-S tri-layers. It has been shown that this compound with a monoclinic crystal structure exhibits an antiferromagnetic (AF) ground state below the Néel temperature T(N) ≈ 140 K. Small deviations from the stoichiometry and some disordering effects caused by the additional low-temperature heat treatment do not affect substantially the AF state in Fe(0.5)TiS(2). According to neutron diffraction data the magnetic structure at 2 K is described by the propagation vector k = (1/4,0,1/4). The Fe magnetic moments with a value of (2.9 ± 0.1) μ(B) are directed at an angle of (78.5 ± 1.8)° to the layers. Application of the magnetic field at T < T(N) induces a metamagnetic phase transition to the ferromagnetic (F) state, which is accompanied by the large magnetoresistance effect (|Δρ/ρ| up to 27%). Below 100 K, the field-induced AF-F transition is found to be irreversible, as evidenced by magnetoresistance and neutron diffraction measurements. The magnetization reversal in the metastable F state is accompanied at low temperatures by substantial hysteresis (ΔH ~ 100 kOe) which is associated with the Ising character of Fe ions.

Magnetic and Magnetocaloric Properties of (MnCo) 1- x Ge Compounds

The crystal structure, magnetic properties, and heat capacity of the (MnCo)1 − xGe compounds with x ≤ 0.05 have been studied. It was found that, as the deviation from the MnCoGe stoichiometric composition increases, the temperature of structural transition from the low-temperature phase with the orthorhombic TiNiSi-type structure to the high-temperature phase with the hexagonal Ni2In-type phase decreases rapidly, whereas the magnetic ordering temperature varies slightly. The temperature of structural transition for the composition with x = 0.02 approximately coincides with the Curie temperature of the hexagonal phase, and the transition is accompanied by a significant entropy change, namely, ΔS = 34 J/(kg K). The application of high magnetic field in the transition-temperature range causes an increase in the relative volume of the orthorhombic phase. An analysis of magnetocaloric properties of these compounds, which was performed with the formal application of the Maxwell’s relationship near the temperature of first-order structural phase transition, is shown to give overestimated values of the entropy change.

Magnetic Phase Diagrams of Tm2Fe19-xMnx and Tm2Fe17+δ Systems

The Tm2Fe19-xMnx (x = 0 - 1.5) and Tm2Fe16, Tm2Fe17, Tm2Fe18, Tm2Fe19 intermetallic compounds were synthesized and their magnetic and structural properties were studied. Magnetic measurements, X-ray and neutron diffraction investigations were used. The compounds crystallize in a disordered variant of the hexagonal Th2Ni17-type structure. The lattice parameters a, c increases in the Tm2Fe19-xMnx system, whereas c decreases and a increases in the Tm2Fe19 - Tm2Fe16 system as Fe content decreases. The temperatures of ferromagnetic ordering and spin-reorientation increase as Fe content decreases in these systems. Apparently, the decrease of occupation of defected dumbbell Fe (4e) site causes these regularities.

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.

Layer-preferential substitutions and magnetic properties of pyrrhotite-type Fe7-yMyX8 chalcogenides (X = S, Se; M = Ti, Co).

A comparative study of four series of pyrrhotite-type chalcogenide compounds Fe(7-y)M(y)X(8) (X = S, Se) with substitution of Ti or Co for iron has been performed by means of x-ray and neutron powder diffraction, and by magnetization measurements. In Fe(7-y)M(y)X(8) compounds having a ferrimagnetic order at y = 0, the substitution of either Ti or Co for iron is observed to result in a monotonous decrease of the magnetic ordering temperature, while the resultant magnetization shows a non-monotonous behavior with a minimum around y = 1.0-1.5 in all the Fe(7-y)M(y)X(8) families except Fe(7-y)Co(y)Se(8). Suppression of a magnetically ordered state with substitutions in Fe(7-y)M(y)X(8) is ascribed to nearly zero values of Ti and Co magnetic moments, while the non-monotonous changes of the resultant magnetization are explained by the compensation of the sublattice magnetizations due to the non-random substitutions in alternating metallic layers. The difference in the cation partitioning observed in Fe(7-y)Ti(y)X(8) and Fe(7-y)Co(y)X(8) is attributed to the difference in the spatial extension of Ti and Co 3d orbitals. High coercive field values (20-24 kOe) observed at low temperatures in the Ti-containing compounds Fe(7-y)Ti(y)X(8) with y ⩾ 3 are suggested to result from the enhancement of Fe orbital moment due to the Ti for Fe substitution.

Pressure Induced AF - F - AF Magnetic Phase Transformations in Pd Substituted FeRh Compound

At ambient pressure, the Fe0.49(Rh1-xPdx)0.51 alloys with the Pd concentration within 0 < x < 0.12 exhibit an antiferromagnetic (AF) state below the critical temperature Tt, while above x = 0.12 the alloys have a ferromagnetic (F) order up to the Curie temperature TC 650 K. The temperature and field dependences of the magnetization in the alloys with x = 0.08; 0.13 were investigated under hydrostatic pressure up to 10 kbar. The application of pressure of about 8.5 kbar is observed to induce the F-AF phase transition in the ferromagnetically ordered compound with x = 0.13. The AF-F-AF phase evolution was revealed with increasing pressure in the AF-ordered alloy with x = 0.08.

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.

Structure and magnetic properties of Nd9Fe74B12Ti4C rapidly quenched alloys prepared by melt electrospinning using centrifuge technique

The X-ray diffraction analysis and magnetometry methods were used to investigate the phase composition and magnetic properties of rapidly quenched Nd9Fe74B12Ti4C alloys. The rapidly quenched alloys were prepared by the spinning of the melt of a specified composition using a centrifuge technique with the use of electric current passing through an injected stream during quenching. The rapidly quenched alloys in the form of flakes (plane fragments of a metal ribbon) were subjected to short-term annealing in the temperature range between 550–1000°C. It was found that the alloy prepared with passage of an electric current contains a larger amount of amorphous phase than that prepared without passage of an electric current. This fact is reflected in the difference between the processes of their devitrification during short-term annealing. The anisotropy of hysteresis properties of flakes annealed at 720°C was discovered along and in the plane perpendicular to the planes of flakes (of a “fanlike” texture) during their magnetizing.