E. A. Tereshina

Magnetic anisotropy and magnetostriction in a Lu2Fe17 intermetallic single crystal

The magnetic anisotropy and magnetostriction of a Lu2Fe17 single crystal are investigated. The temperature dependence of the magnetic anisotropy constant K1 is measured in the range 4.2–300 K. The results obtained are compared with the data calculated using the Callen theoretical formula. It is found that the temperature dependence of K1 for the Lu2Fe17 single crystal deviates from the temperature curve predicted by the localized single-ion model. The inference is drawn that a certain contribution to the magnetic anisotropy of the Lu2Fe17 compound is made by the magnetic anisotropy of band electrons. The longitudinal, transverse, and volume magnetostrictions of the Lu2Fe17 single crystal are studied, and the magnetostriction constants are calculated. It is demonstrated that the exchange integral of Lu2Fe17, as for the Y2Fe17 compound, substantially depends on the atomic volume. This dependence is responsible for the considerable difference between the Curie temperatures of the Lu2Fe17 and Y2Fe17 compounds. It is revealed that the magnetostriction of the Lu2Fe17 single crystal in the temperature range of the magnetic phase transition is determined by the two-ion exchange and single-ion contributions.

Magnetocaloric properties of distilled gadolinium: Effects of structural inhomogeneity and hydrogen impurity

High-purity Gd prepared by distillation is a structurally inhomogeneous system consisting of needle-shaped crystals of cross section 0.5–2.5 μm with near-c-axis orientation embedded in a matrix of nanosized (30–100 nm) grains. By measuring the magnetocaloric effect (MCE) directly, we find that the MCE values differ markedly for the plate-shaped samples cut out of a distillate along and perpendicular to the crystals. The effect of small controlled amounts of impurity (hydrogen) on the properties of distilled Gd is further studied. We observe opposite trends in the MCE response to hydrogen charging with respect to the crystals orientation within the samples and discuss mechanisms interrelating the unique structural morphology with the impurity behavior. As an overall assessment, the Curie temperatures of α-GdHx solid solutions increase from 291 K up to 294 K when increasing hydrogen concentration x from 0 to 0.15. Hydrogenation is found to broaden the ferromagnetic-to-paramagnetic phase transition. Hydroge...

Variation of the intersublattice exchange coupling due to hydrogen absorption in Er2Fe14B: a high-field magnetization study

Single crystals of a series of hydrides Er2Fe14BHx (x ≤ 2.5) have been produced and studied in pulsed magnetic fields up to 60 T. The magnetization curve of Er2Fe14B in the easy direction [100] features a stepwise anomaly at about 45 T, corresponding to the first-order phase transition. A similar magnetization jump is also present in the curve along [110], but at a higher field, ∼52 T. The [100] data of the parent and hydrogen-charged Er2Fe14BHx with x = 0.25, 1.5, 2.5 were used to deduce the Er-Fe molecular field Hmol as a function of hydrogen content x. After moderate initial decrease, Hmol(x) drops abruptly above x = 1.5. Hydrogenation results in a 12% reduction of the Er-Fe molecular field in Er2Fe14BH2.5 as compared to Er2Fe14B. For reference, influence of hydrogen on Hmol in an Er2Fe17-H system is also presented.

Multifunctional Phenomena in Rare-Earth Intermetallic Compounds With a Laves Phase Structure: Giant Magnetostriction and Magnetocaloric Effect

We report on the magnetic and thermal properties [magnetization, specific heat, thermal expansion, magnetostriction, and magnetocaloric effect (MCE)] for the three multicomponent systems Tb_xDy_yGd_zCo₂, Tb_xDy_yHo_z(Co, Fe)₂, and Tb_xDy_yEr_z(Co, Fe)₂ (x + y + z = 1). We show that for Tb_xDy_yR_zCo₂, the Curie temperatures, TC (which ranged from 130 to 300 K), and order of the phase transition (first or second order) could be controlled by composition. The highest MCE values (the adiabatic temperature change ΔT_ad = 2.2-2.3 K at μ₀ΔH = 1.8 T) were observed for the compounds exhibiting the transitions of the first order. Giant volume magnetostriction of 1500-2000 and 500-600 ppm is demonstrated at a field of μ₀H = 10 and 1.2 T, respectively. Structural and magnetic entropy contributions to the total isothermal entropy change are estimated for Tb_xDy_yR_zCo₂. Regular recurrence and/or change of the physical properties across the varied composition of the compounds allows us to find the materials with desired magnetic characteristics, such as T_C, MCE, and magnetostriction, to use them in practice.

Magnetocaloric and magnetoelastic effects in (Tb0.45Dy0.55)1-xErxCo2 multicomponent compounds

The magnetocaloric effect (MCE) and magnetoelastic (ME) anomalies at the magnetic phase transitions in (Tb0.45Dy0.55)1-xErxCo2 compounds (0.1 ≤ x ≤ 0.3) are studied. For the compounds synthesized with the use of high-pure rare-earth metals, the measurements of MCE performed by a direct method and the study of magnetostriction and thermal expansion by a strain-gauge technique are carried out. Large MCE and a maximum of magnetostriction are observed in the vicinity of phase transitions in the studied compounds, which can be considered as potential materials for magnetic refrigeration. It is shown that the magnetoelastic energy contribution to the MCE for (Tb0.45Dy0.55)1-xErxCo2 cannot be neglected.

Magnetocaloric effect in (Tb,Dy,R)(Co,Fe)2 (R = Ho, Er) multicomponent compounds

The magnetic, magnetocaloric, and magnetoelastic properties of TbxDyyRz(Co,Fe)2 (R = Ho, Er; x + y + z = 1) single-phase alloys prepared by arc melting were investigated. The high-purity samples with various compositions were used for the study, and a comprehensive investigation of the properties was performed. The measurements of the magnetocaloric effect (MCE) were carried out by a direct method; and the magnetostriction was determined using the strain-gauge technique. In the vicinity of the magnetic phase transition, an abrupt change of the magnetization, a large MCE, and the maxima of volume magnetostriction were observed for the compounds studied. Obtained results of MCE in (Tb,Dy)Co2 agree well with available theoretical calculations.

Magnetic ordering temperature of nanocrystalline Gd: enhancement of magnetic interactions via hydrogenation-induced “negative” pressure

Gadolinium is a nearly ideal soft-magnetic material. However, one cannot take advantage of its properties at temperatures higher than the room temperature where Gd loses the ferromagnetic ordering. By using high-purity bulk samples with grains ~200 nm in size, we present proof-of-concept measurements of an increased Curie point (TC) and spontaneous magnetization in Gd due to hydrogenation. From first-principles we explain increase of TC in pure Gd due to the addition of hydrogen. We show that the interplay of the characteristic features in the electronic structure of the conduction band at the Fermi level in the high-temperature paramagnetic phase of Gd and “negative” pressure exerted by hydrogen are responsible for the observed effect.

Magnetostriction in (Tb0.45Dy0.55)1−xErxCo2 (x = 0.1, 0.2): high-field investigation

Intermetallic compounds (Tb0.45Dy0.55)1−xErxCo2 (x = 0.1; 0.2) were synthesized using high purity rare-earth metals. Multicomponent compositions with compensated magnetic anisotropy (MA) were chosen with respect to theoretical predictions based upon the single-ion MA model. Magnetostriction was measured in magnetic fields up to 10 T within the temperature range of 1.5–200 K by means of strain gauges. In the vicinity of magnetic phase transitions (160–170 K), giant volume magnetostriction (~2×10−3 in 10 T) provided by the band magnetism of a Co sublattice was observed in the compounds studied.

Magnetic Properties of Zr-Doped Lu

Influence of Zr-substitution on magnetic properties of (Lu

_{2}

_{1-x}