A. Apostolov

Magnetic properties and magnetic structure of HoFe11Ti and its hydrides

Abstract The hydrogenation effect on some structural and magnetic properties of the intermetallic compound HoFe 11 Ti was investigated. The absorbed hydrogen causes the appearance of a spin reorientation transition. The temperature of this transition, as well as the magnetic ordering temperature were determined as a function of the hydrogen concentration. The temperature dependencies of the magnetic moment of 8i, 8j, 8f iron and Ho atoms and the unit cell parameters were determined using neutron diffraction methods.

Hydrogen desorption characteristics of MmNi5−xFex compounds☆

Hydrogen desorption in mischmetal intermetallics MmNi5−xFex (x = 0.3, 0.5, 0.7, 0.85, 1.0) prepared by arc melting were studied in the range 0–40 °C. The substitution of iron for nickel causes a decrease in the hydrogen dissociation pressure. This substitution does not, in practice, change the maximum hydrogen capacity (6.1−5.8 H atoms per formula unit) in the range x = 0.3−0.7, but for x > 0.7 it decreases considerably.

The effect of absorbed hydrogen on the magnetic properties of DyFe11Ti

Abstract The effect of absorbed hydrogen on the structural and magnetic properties of DyFe 11 Ti has been investigated. The compound DyFe 11 Ti was hydrogenated to the composition DyFe 11 TiH x , where x ranges from 0 to 1.5. The absorption hydrogen pressure-composition isotherms of the hydrides indicate solid solution behavior. Hydrogen absorption does not change the tetragonal structure of the host compound but is accompanied by an expansion in unit cell volume. Magnetic characteristics of the host material and its hydrides (measured in situ in a hydrogen atmosphere) were investigated over the temperature range 77–700 K and at applied fields up to 12 kOe. Upon hydrogenation the magnetic ordering temperature T c as well as the spin-reorientation temperatures T sr are observed to increase. Moreover, the incorporation of hydrogen leads to an expansion of the temperature range in which the magnetic anisotropy of the rare-earth sublattice dominates over that of the iron sublattice.

A change in magnetic properties of R2Co7 intermetallic compounds (R = Pr, Sm, Tb and Ho) upon hydrogen absorption

Abstract The magnetic properties of the compounds R2Co7 (R = Pr, Sm, Ho and Tb) and their hydrides with hydrogen concentration corresponding to β and γ phases are studied. Ferro to spin-glass magnetic transitions are found upon the β hydride phase formation in Tb2Co7 and Ho2Co7-ferri-magnetics. Strong reductions in exchange interactions and Tc for R2Co7 hydrides phases are observed.

Apparatus for in situ measurements of influence of hydrogen absorption on the magnetic properties of intermetallic compounds

Abstract A laboratory apparatus for studying in situ change of magnetic properties of the intermetallic compounds upon hydrogen absorption was constructed. Both magnetization and Pressure Temperature Concentration (PTC) relations are determined simultaneously by using a combination of the extraction magnetometer and PTC-measuring unit. Absorbed or desorbed amounts of hydrogen are measured volumetrically.

Neutron diffraction study of HoFe11TiDx deuterides

Abstract Powder neutron diffraction measurements have been performed on the HoFe 11 TiD x ( x =0, 0.7, 0.9) compounds. The results show the appearance of a spin–reorientation transition and a remarkable change of the crystallographic parameters and the magnetic moments of the Fe atoms after deuteration.

A change in magnetic and structural properties of the CeFe11Ti intermetallic compound upon hydrogen absorption

Abstract The intermetallic compound CeFe11Ti and corresponding hydride with H-concentration 0.55 at H/mole have been prepared; we present a study of the hydrogenization effect on some structural and magnetic properties. The alloy exhibited tetragonal ThMn12 structure. Hydrogenization expands the lattice without change of structure type. The host material and hydride are ferromagnetics. Hydrogenization increases Tc from 503 to 553 K as well as the net magnetic moment.

Magnetic properties of amorphous Gd4Fe3 and Y4Fe3 alloys

Abstract Amorphous alloys with non-S state rare earth ions (Gd 4 Fe 3 and Y 4 Fe 3 ) are prepared as ribbons. The amorphism is proved by X-ray diffraction and differential scanning calorimetry. The crystallization of the alloys was studied using a variable heating rate and the results were analysed by Kissingers method. The phases formed during the crystallization process were identified by means of X-ray diffraction and thermomagnetic measurements. The magnetic properties were investigated from 4.2 to 400 K in steady fields of up to 140 kOe. A spin-glass-like behaviour was observed for the amorphous Y 4 Fe 3 alloy and this was due to the presence of both positive and negative exchange interactions. The observed reduction in the iron magnetic moment was discussed in terms of the environmental model of Jaccarino and Walker. The magnetic properties of the alloys investigated were compared with those of similar rare earth alloys containing cobalt instead of iron.

Correlation between the magnitude of structural disorder and the frustration of magnetic order in Gd4Mn3 metallic glass

Abstract The magnetic properties of Gd 4 Mn 3 amorphous alloy have been investigated by ac and dc susceptibility measurements in the temperature range from 4.3 to 500 K. The alloy has been found to exhibit a re-entrant magnetic behaviour with paramagnetic to ferromagnetic to spin-glass-like state transitions at T c = 167 K and T f = 72 K, respectively. The radial distribution function for Gd 4 Mn 3 glass has been determined; the partial atomic distances and the partial coordination numbers have been estimated on the basis of a detailed structural analysis. The relationship between the magnitude of structural disorder and the frustration of magnetic order in Gd 4 Mn 3 glass has been clarified from the comparison of its structural and magnetic properties with those of Gd 4 T 3 glasses (T = Al, Cu).

Magnetic Properties of Some Solid Amorphous Rare Earth Alloys

The amorphous state is a metastable state, its structure characterized by a topological short-range order and an absence of long-range order. Nevertheless, in the majority of amorphous substances containing magnetic atoms or ions a strong long-range order exists under certain conditions. The magnetic properties of these substances show a prevailing difference of the temperatures of magnetic transitions from those of the respective crystal analogues, and the values of the spontaneous magnetizations in the amorphous state are smaller than those in a crystalline state.