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A novel metastable phase of DyGe2.85 synthesised in the AuCu3-structure under high pressure, has been studied by means of the magnetic susceptibility and electrical resistivity measurements (under the pressure P ≤ 3.1 GPa), neutron powder diffraction and time-differential γ-γ perturbed angular correlations (TDPAC) using 111Cd nuclear probes. Two distinct phase transitions have been found in this compound as the temperature is lowered. We assign the first transition occurring at the temperature T CDW = 80 K with charge density wave formation and the second transition at T N ≈ 18 K with an antiferromagnetic spiral ordering of Dy magnetic moments, and discuss a close relationship between them.

In this paper the charge density wave (CDW) and magnetic ordering for the high-pressure phase of ${\mathrm{TbGe}}_{2.85}$ with the ${\mathrm{AuCu}}_{3}$ structure have been studied by means of electrical resistivity and neutron powder diffraction at pressures up to 3 and 5 GPa, respectively. The electrical resistivity measurements showed that the charge density wave transition temperature ${T}_{\mathrm{CDW}}$ decreases with increasing the external pressure and the CDW transition in ${\mathrm{TbGe}}_{2.85}$ is suppressed at $P\ensuremath{\ge}2.6\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$. The N\'eel temperature ${T}_{N}$ is approximately independent of the pressure. The neutron powder diffraction at low temperatures and high pressures reveals the appearance of the second magnetic commensurate phase at $P=1.2\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ with wave-vector $\mathbf{k}=(1/2,0,0)$. The calculation of the electronic structure of the ${\mathrm{TbGe}}_{3}$ (${\mathrm{AuCu}}_{3}$-type structure) compound was also performed. The high value of the electronic states at the Fermi level confirms the instabilities of the stoichiometric compound ${\mathrm{TbGe}}_{3}$.

New cubic phases of YbGe2.85, TbGe2.85 and DyGe2.85 crystallized in the AuCu3 structure are synthesized at a pressure of 8 GPa. Using the differential perturbed angular γγ-correlation method (TDPAC) we measure the electric field gradient Vzz (the quadrupole frequency ν Q = eQV ZZ / h ) at 111Cd nuclei probes inserted in Ge vacancy lattice sites for all these compounds. In YbGe2.85 the electric field gradient (EFG) is obtained as a function of pressure (up to 8 GPa) at room temperature and as a function of temperature (down to 4 K) at normal pressure. In TbGe2.85 and DyGe2.85 EFG is measured only as a function of temperature (down to 77 K) at normal pressure. In YbGe2.85 the change of EFG and νQ with pressure indicate a change of Yb valance from 2.46 at normal pressure to 2.89 at 8 GPa. In all compounds EFG and νQ are found to be practically independent of temperature.

We have synthesized polycrystalline samples of EuFe2As2 by melting the stoichiometric mixture of constituent components at a high pressure (HP) of 8 GPa and measured the properties of HP-synthesized samples at ambient and high pressure up to 6 GPa. SDW-type antiferromagnetism appears below 150 K and Eu-related antiferromagnetism appears below 16 K in all HP synthesized samples. Also, all HP-synthesized samples exhibit superconductivity with Tc = 20–30 K at ambient pressure, though a zero-resistance state has not been observed. This superconductivity is very robust against application of magnetic field (dHc2/dT = −3.2 T K−1) and pressure (a tiny signal of superconductivity is still detectable below 2.5 K at 5.8 GPa). SDW antiferromagnetism is suppressed under pressure and is not observed above 1.7 GPa and below 60 K. The temperature of the magnetic ordering of Eu2+ moments increases under pressure. Specific heat measurements in a magnetic field reveal an increase of this temperature in field, therefore indicating field-induced ferromagnetism in the Eu sublattice.

The time differential perturbed angular γγ-correlation method (TDPAC) has been used to study the hyperfine quadrupole interaction (HQI) of 111 Cd probe nuclei introduced in the novel cubic phase of UGe2 (the AuCu3 crystal lattice). The HQI parameters have been measured as a function of pressure up to 8 GPa. At normal pressure the TDPAC spectrum is described by a single quadrupole frequency of 101.8 MHz. The quadrupole frequency increases with pressure to 118.4 MHz at 5.5 GPa. At a pressure of 7.0 GPa the TDPAC spectrum becomes complex and can be fit by two characteristic quadrupole frequencies: ν 1Q = 117 MHz and ν 2Q = 147 MHz. The appearance of the second quadrupole frequency of 111 Cd probe nuclei has been ascribed to a signal from 111 Cd probes in U sites, which become effective due to a structural phase transition in UGe 2 .

Itinerant magnets generally exhibit pressure induced transitions towards non magnetic states. Using synchrotron based X-ray diffraction and emission spectroscopy, the evolution of the lattice and spin moment in the chiral magnet MnGe was investigated in the paramagnetic state and under pressures up to 38 GPa. The collapse of spin-moment takes place in two steps. A first-order transition with a huge hysteresis around 7 GPa transforms the system from the high-spin at ambient pressure to a low-spin state. The coexistence of spin-states and observation of history-depending irreversibility is explained as effect of long-range elastic strains mediated by magnetovolume coupling. Only in a second transition, at about 23 GPa, the spin-moment collapses., Comment: 10 pages, 9 figures, includes supplement

We have studied by muon spin resonance ({\mu}SR) the helical ground state and fluctuating chiral phase recently observed in the MnGe chiral magnet. At low temperature, the muon polarization shows double period oscillations at short time scales. Their analysis, akin to that recently developed for MnSi [A. Amato et al., Phys. Rev. B 89, 184425 (2014)], provides an estimation of the field distribution induced by the Mn helical order at the muon site. The refined muon position agrees nicely with ab initio calculations. With increasing temperature, an inhomogeneous fluctuating chiral phase sets in, characterized by two well separated frequency ranges which coexist in the sample. Rapid and slow fluctuations, respectively associated with short range and long range ordered helices, coexist in a large temperature range below T$_{N}$ = 170 K. We discuss the results with respect to MnSi, taking the short helical period, metastable quenched state and peculiar band structure of MnGe into account., Comment: 13 pages, 11 figures

The capacity of YMn 2 to undergo reversible hydrogenization makes this compound a potential candidate for hydrogen storage. This report describes the successful synthesis of YMn 2 H 6 from hexagonal C14 YMn 2 as well as calorimetric studies of hexagonal C14 YMn 2 , cubic C15 YMn 2 and their isostructural derivatives, YMn 2 H 6 and YMn 2 D 6 . Complementary structural and physical property characterizations include X-ray diffraction, electrical resistivity, and magnetic susceptibility measurements. Of particular interest is a hysteretic first-order phase transition in C15 YMn 2 near 100 K, which does not occur in C14 YMn 2 . Analysis of a specific heat anomaly that is associated with this transition reveals a substantial latent heat of 330 J/mol. No such anomalous specific heat exists in YMn 2 D 6 , suggesting that the transition is suppressed upon deuterization.

We use the time-differential perturbed angular correlation technique to study nuclear electric quadupole hyperfine interactions of probe 111Cd nuclei in cerium lattice sites at room temperature under pressures up to 8 GPa. We have found that the well known γ → α phase transition in cerium is not isostructural. In α-Ce, the probe 111Cd nuclei reveal a quadrupole electron charge density component that is absent in γ-Ce. The hidden spacial structure of electronic quadrupoles in α-Ce is triple-q antiferroquadrupolar, as was suggested in [14]. We relate our findings to the current understanding of the γ → α phase transition and also report on nuclear quadrupole interactions in other high-pressure phases of cerium: α″ (C2/m space symmetry) and α′ (α-U structure).

The time-differential perturbed angular correlations technique (TDPAC) has been employed for measuring the parameters of hyperfine interactions in earlier known RAl 3 compounds, synthesized at high pressure (8 GPa) and high temperature, where R = La, Ce, Sm, Gd, Tb, Dy, Ho, Er, Yb and Lu. The 111 Cd( 111 In) radioactive atom was used as a probe nucleus. The X-ray method has revealed that with the increase in the atomic number of a rare-earth element R, the obtained RAl 3 high-pressure phases crystallize, respectively, into orthorhombic, hexagonal and cubic structures. It has been found that in the compounds containing R=La, Ce, Sm and Gd, a deviation from earlier known structural types and the formation of new ones is observed, which is associated with the change of the stoichiometric composition of the said compounds. The results of the PAC measurements have confirmed the deviation from the predetermined stoichiometric composition 1R:3Al for the compounds LaAl 3 , CeAl 3 , SmAl 3 and GdAl 3 and have verified the RAl 3 stoichiometric structure for the other high-pressure phases obtained in this work.

Temperature dependencies of the electrical resistivity, magnetic susceptibility, and heat capacity have been obtained in the cubic phase of ${\mathrm{TbGe}}_{2.85}$ (the ${\mathrm{AuCu}}_{3}$ structure), synthesized at high pressure. The macroscopic measurements indicate that a charge density wave is formed below 145 K and an antiferromagnetic ordering is realized below 19 K. Hyperfine interaction data obtained with the time differential perturbed angular correlation method with $^{111}\mathrm{Cd}$ probes inserted in the ${\mathrm{TbGe}}_{2.85}$ lattice suggest that the charge density wave is incommensurate in the temperature region 19--145 K, but becomes commensurate below 19 K. The neutron diffraction reveals a complex antiferromagnetic spiral structure in the magnetically ordered phase. We discuss relations between the charge density wave and helical ordering in ${\mathrm{TbGe}}_{2.85}$ and ${\mathrm{TbPd}}_{3}$.

Time differential perturbed angular gamma-gamma-correlation (TDPAC) method on 111Cd nuclei probes inserted in ZrZn1.9 is used to measure the magnetic hyperfine fields (MHF) at Zr and Zn sites and the electric field gradient (EFG) Vzz at Zn sites as a function of temperature at various pressures and as a function of pressure at the temperature 4 K. Our data indicate that the local magnetic moment of Zr in the magnetically ordered state is substantially larger than its value obtained from the macroscopic measurements and that there is also an induced magnetic moment at the Zn site. We conclude that ZrZn2 is not a simple ferromagnet and discuss a possible type of its magnetic ordering., 7 pages, 6 figures, submitted for publication

Magnetic properties of hydrogen-amorphized LaCo2 with a relatively high hydrogen concentration, LaCo2H3.8, were investigated by magnetization and NMR measurements. The hydride behaves as a ferromagnet with TC = 400–500 K and averaged moment ∼0.5 μB/Co (at 1.5 K). The Co moment amplitude was found to distribute considerably from 0 to ∼1 μB. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The ground-state magnetism of a high-pressure-synthesized cubic Laves phase compound LaCo 2 was investigated by 59 Co NMR experiments. At low temperatures, we found two kinds of NMR signals corresponding to small internal fields, -2.8 and 0.1 T, which are separated due to the anisotropy in the hyperfine field. This result reveals the weak ferromagnetism in LaCo 2 , indicating that a small spontaneous Co moment can exist in rare-earth–cobalt Laves phase compounds with neither a molecular exchange field from rare-earth atoms nor effects of disorder. The ordered moment and the easy magnetization axis are estimated to be

Nuclear magnetic resonance measurements were performed for high-pressure synthesized alkaline-metal-cobalt Laves phase compounds, cubic CaCo 2 and hexagonal MgCo 2 . 59 Co ferromagnetic nuclear resonances corresponding to hyperfine fields of -15.7 and -8.0 T were found for CaCo 2 and MgCo 2 , respectively, indicating relatively large spontaneous Co moments in these compounds in contrast to zero or induced Co moments in the rare-earth-cobalt Laves phase system.

We have studied the MnGe chiral magnet below ${T}_{\text{N}}=170$ K, by magnetic measurements, M\"ossbauer spectroscopy, and by neutron diffraction at ambient and under nonhydrostatic pressure. At ambient pressure, we observe the coexistence of two magnetic phases belonging to the same crystal phase in a large temperature range (down to 100 K) below ${T}_{\mathrm{N}}$: ferromagnetically correlated rapidly fluctuating spins coexist with frozen spins involved in the helical order. Applying a uniaxial pressure component induces a strong magnetic texture, where most of the helical axes reorient along the stress axis. The magnetic texture persists in the fluctuating chiral state up to ${T}_{\mathrm{N}}$. Our results suggest that the zero field ground state at ambient pressure is a multidomain state consisting of helical domains with random orientations rather than a three-dimensional skyrmion lattice. They show the presence of an unusually broad transition to paramagnetism with a dynamical phase separation triggered by temperature.

International audience; Cubic helimagnets such as MnSi and FeGe have provided paradigmatic cases of pressure-induced collapse of band ferromagnetism in metals, accompanied with exotic partial order and chiral spin textures. Isostructural MnGe stands out owing to its much shorter helix pitch and high magnetic moment. By combining resistivity, ac susceptibility, and neutron diffraction measurements under very high pressure, we show that the helical order in MnGe transforms around 6 GPa from a high-spin to a low-spin state, recalling the weak ferromagnetism of MnSi at ambient pressure. Helical order collapses only above 10 GPa. The spin-state transition is supported by ab initio calculations.

Radioactive 111 In was introduced into the Laves phases YMn 2 , GdFe 2 and YbFe 2 synthesized under pressure of 8 GPa, and the hyperfine interaction of the daughter 111 Cd was measured by the perturbed angular correlation method. In the obtained hexagonal (C14) phase YMn 2 111 In is substituted for Mn, predominantly at h-sites, experiencing there an electric quadrupole interaction with ν Q = 32.0(5) MHz and η = 0.51(5) at 300 K. In GdFe 2 and YbFe 2 (cubic C15) most of the 111 In-1 1 Cd probes (80%) substituted mainly for the rare earth atoms and experienced a magnetic hyperfine field |B hf | = 2.92(4) T and 3.32(7) T, respectively, at 300 K. The results are discussed together with the published data for the normal cubic YMn 2 , and for LuFe 2 and ZrFe 2 .

Magnetic ground-state and dynamical properties of high-pressure synthesized YbMn2 were characterized microscopically by 55Mn NMR experiments. A 55Mn spectrum indicates that YbMn2 is paramagnetic down to 4.2 K. The nuclear spin-lattice relaxation is dominated by the Yb moment fluctuations below 30 K and by Mn spin fluctuations with antiferromagnetic correlations at higher temperatures.

The ground state magnetic properties of high-pressure synthesized Laves phase compounds with the hexagonal C14 structure, DyMn 2 , TbMn 2 and GdMn 2 , were investigated by 55 Mn nuclear magnetic resonance technique and compared with those of the equilibrium phases with the cubic C15 structure. We observed two different signals in zero field for DyMn 2 , which are just the same as those for the C15 phase, indicating the coexistence of magnetic and non-magnetic manganese sites. For TbMn 2 , a zero-field spectrum with two peaks was observed in the frequency range below 80 MHz, suggesting that the manganese moment becomes unstable and that manganese atoms are partially non-magnetic, which is in contrast to large and stable magnetic moments in the C15 phase. For GdMn 2 , a broad zero-field spectrum was observed just in the same frequency range as that of the C15 phase, indicating that all manganese atoms have stable large moments.

The magnetic structure of cubic MnGe has been determined by powder neutron diffraction. MnGe has a helical spin structure with a propagation vector $\mathbf{k}=(0,0,\ensuremath{\zeta}$), where $\ensuremath{\zeta}=0.107(5)$ just below the transition temperature ${T}_{N}=170$ K. The $\ensuremath{\zeta}$ value increases upon cooling and locks in to the value of 0.167(4) below 30 K. The moment value is 2.3(5)${\ensuremath{\mu}}_{B}$ at 2 K. The onset of the magnetic order is connected with a symmetry lowering from cubic to orthorhombic.

Using time-differential perturbed angular correlation spectroscopy we have measured the electric field gradient (EFG) at $^{111}\text{C}\text{d}$ probe nuclei in solid Ce in a pressure range up to 8 GPa. Covering various allotropic phases of Ce, we find that the value of the EFG in the cubic $\ensuremath{\alpha}$ phase is almost four times larger than in the cubic $\ensuremath{\gamma}$ phase and close to values in the noncubic phases ${\ensuremath{\alpha}}^{\ensuremath{'}}$ and ${\ensuremath{\alpha}}^{\ensuremath{''}}$. These results together with the differences in time modulation of the spectra are interpreted as evidence for quadrupolar electronic charge-density ordering and symmetry lowering at the $\ensuremath{\gamma}\ensuremath{\rightarrow}\ensuremath{\alpha}$ transition while the lattice remains face-centered cubic.

We synthesized tetragonal alpha-FeSe by melting a powder mixture of iron and selenium at high pressure. Subsequent annealing at normal pressure results in removing traces of hexagonal beta- FeSe, formation of a rather sharp transition to superconducting state at Tc ~ 7 K, and the appearance of a magnetic transition near Tm = 120 K. Resistivity and ac-susceptibility were measured on the annealed sample at hydrostatic pressure up to 4.5 GPa. A magnetic transition visible in ac-susceptibility shifts down under pressure and the resistive anomaly typical for a spin density wave (SDW) antiferromagnetic transition develops near the susceptibility anomaly. Tc determined by the appearance of a diamagnetic response in susceptibility, increases linearly under pressure at a rate dTc/dP = 3.5 K/GPa. Below 1.5 GPa, the resistive superconducting transition is sharp; the width of transition does not change with pressure; and, Tc determined by a peak in drho/dT increases at a rate ~ 3.5 K/GPa. At higher pressure, a giant broadening of the resistive transition develops. This effect cannot be explained by possible pressure gradients in the sample and is inherent to alpha-FeSe. The dependences drho(T)/dT show a signature for a second peak above 3 GPa which is indicative of the appearance of another superconducting state in alpha-FeSe at high pressure. We argue that this second superconducting phase coexists with SDW antiferromagnetism in a partial volume fraction and originates from pairing of charge carriers from other sheets of the Fermi surface.

High pressure was used to synthesize the unremitting series of the cubic Laves phase pseudobinary alloys of the composition Y(Fe1−xNix)2. The lattice constant, the magnetovolume, the magnetic moment per transition metal ion and the Curie temperature as a function of Ni concentration are reported for Y(Fe1−xNix)2 system. On these dependences have been observed the Invar-type anomaly. It has been concluded that the Ni ions in the Y(Fe1−xNix)2 alloys have a magnetic moment of about 0.36μmB for all values of x. The magnetic behavior of Ni is connected with the electronic phase transition which takes place when the Y(Fe1−xNix)2 alloys are crystallized under the influence of a high pressure.

The quadrupole interaction at $^{111}\mathrm{Cd}$ impurity nuclei in the intermediate-valence compound $\mathrm{Yb}{\mathrm{Al}}_{2}$ has been measured under pressure up to $80\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$ by the time-differential perturbed angular correlation spectroscopy. It was found that the quadrupole frequency ${\ensuremath{\nu}}_{Q}$ measured on the $^{111}\mathrm{Cd}$ nuclei located at the Al sites in $\mathrm{Yb}{\mathrm{Al}}_{2}$ varies nonlinearly and increases by almost four times with the pressure increase up to $80\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. A linear correlation between the mean Yb valence, derived from Yb ${L}_{3}$ OFY-XAS and RXES measurements, and the electric field gradient (the quadrupole frequency ${\ensuremath{\nu}}_{Q}=eQ{V}_{zz}∕h$) has been observed. The quadrupole frequencies on $^{111}\mathrm{Cd}$ in the $\mathrm{Gd}{\mathrm{Al}}_{2}$, $\mathrm{Yb}{\mathrm{Al}}_{3}$, $\mathrm{Tm}{\mathrm{Al}}_{3}$, and $\mathrm{Ca}{\mathrm{Al}}_{2}$ compounds have been also measured. The possibility of determining the valence of Yb in the Yb compounds with $p$ metals from the relation ${\ensuremath{\nu}}_{Q}\mathbf{(}\ensuremath{\upsilon}(P)\mathbf{)}={\ensuremath{\nu}}_{2}+({\ensuremath{\nu}}_{3}\ensuremath{-}{\ensuremath{\nu}}_{2})\ensuremath{\upsilon}(P)$ has been considered.

The specific heat of C14 YMn 2 , YbMn 2 and ThMn 2 was measured in the temperature range of 1.4 K to 10 K. The huge values of specific heat were observed for all compounds. The origin of the huge values of specific heat are considered to be derived from two mechanisms. For C14 YMn 2 and ThMn 2 , those are ascribed to the excitations of large spin fluctuations of Mn moments. On the other hand, the extraordinary large value of YbMn 2 is due to the paramagnetic Yb moment.

The cubic Laves phase NdFe 2 was synthesized by melting at the pressure of 8 GPa the constituents with a small admixture of HfFe 2 . The hyperfine magnetic field at Ta at the Nd sites was measured by the PAC method in the temperature range 97–635 K. The value of the hf field extrapolated to T =0 K is -4.7(3) T; it reaches its maximum absolute value 7.2 T at 420 K.

The transition from the “normal” electronic state in the cubic Laves intermetallics GdFe 2 into a metastable one, created by melting and crystallization of the samples at high pressure, is studied by TDPAC measurements of the magnetic hyperfine fields at 181 Ta in the samples prepared at 3.0, 5.6 and 6.3 GPa.

The hyperfine magnetic fields for181Ta in the cubic (C 15) Laves phases LuFe2 and GdFe2 have been measured by the TDPAC method. At 300 K, Bhf=−20.5(4) T for LuFe2 and +19.0(5) T and +10.2(4) T for the samples of GdFe2, prepared at normal and high (7.7 GPa) pressure, have been obtained. Temperature dependence of these fields in the range 77–900 K has been also measured.

The temperature dependence of powder neutron diffraction for hexagonal C14-Laves-phase TbMn2 and DyMn2 has been measured. Ferromagnetism and antiferromagnetism coexist in TbMn2. The ferromagnetic component continues up to 60 K, whereas the antiferromagnetic component takes its maximum value at around 55 K, begins to decrease above 55 K and vanishes at around 80 K. The magnetic unit cell of the antiaferromagnetism is twice of the chemical one in an a-direction. A presumable magnetic structure has been discussed. For C14-DyMn2, no other structure is observed except for the ferromagnetic one which disappears at around 35 K.

Magnetic properties of metastable C14-RMn 2 Laves phase (R  Y, Gd, Tb, Dy and Yb), have been measured. YMn 2 and YbMn 2 are paramagnetic down to 4.2 K. GdMn 2 , TbMn 2 and DyMn 2 are ferromagnetic at low temperatures and the temperature dependence of their susceptibilities obeys the Curie-Weiss law at high temperatures. An antiferromagnetic order of Mn local moments for GdMn 2 and TbMn 2 has been suggested. These properties are discussed together with those of other stable C14-RMn 2 (R  Pr, Nd, Sm, Ho, Er, Tm and Lu). The onset of local moments of itinerant Mn 3d electrons are mainly determined by the MnMn distance.

C14 YMn 2 synthesized under high pressure was investigated by NMR technique. It was found that C14 YMn 2 is paramagnetic down to the lowest temperature, in contrast with the antiferromagnetic ground state found for C15 YMn 2 . The nuclear spin-lattice relaxation rate of 55 Mn in C14 YMn 2 increases rapidly at low temperatures and tends to saturate above about 50 K, indicating that strong spin fluctuations with antiferromagnetic correlation are rapidly induced on Mn sites by the temperature.

The hyperfine magnetic fields and their temperature dependence for 181Ta in ErFe2 and TmFe2 have been measured by the TDPAC method. Respectively, the following values were obtained at T ≈ 80 K: 16·3(2) T and 17·6(2) T. These data complete those for other RFe2 Laves phases (except CeFe2) obtained earlier and are discussed in common in the framework of the model predicting the induction of the localised 5d moment at Ta ions due to 5d-3d band hybridisation enhanced by the 4f-5d interaction.

The magnetic properties of the Yb6Mn23 intermetallic compound were investigated using magnetometry and neutron diffraction. The Yb6Mn23 phase was found to have a ferrimagnetic structure. The magnetic and chemical unit cells of the compound coincide and the Curie point is 406 K. Neutron diffraction and magnetic measurements at low temperatures indicate that the ytterbium sublattice magnetization rapidly compensates the manganese sublattice magnetization.

The energy band structure for hexagonal TaN is calculated. Die Energiebandstruktur fur hexagonales TaN wird berechnet.

The crystallization of the intermetallic compounds in the MnYb system was investigated at a pressure of 7.7 GPa and temperatures up to 1300°C. The new phases Yb 6 Mn 23 , Yb 2 Mn 17 and Yb 4 Mn 3 , all of which are metastable at room pressure, were found under these conditions.

High pressures and temperatures were used to synthesize the previously unknown compounds Yb3Co, Yb3Ni, Yb2Ni7. The role of chemical contraction and pressure in the formation of Yb-T compounds (T ≡ Mn, Fe, Co, Ni) is discussed.

High pressure synthesis and magnetic measurements are reported for YFeCu, GdFeCu and Yb(Fe 1 − v Cu v ) 2 . In all the alloys evcept Yb(Fe 1 − v Cu v ) 2 , for 0.5 v ⩽ 1, high Curie temperatures were found. The Yb(Fe 1 − v Cu v ) 2 alloys with the copper contents up to 5 at.% have a compensation point. At other copper concentrations and at low temperatures and in low magnetic fields the reduction of the magnetic moment of ytterbium and freeving effects were observed. The magnetivation data were interpreted on the basis of the occurrence of a magnetic moment at the copper atoms for some copper concentrations.

The formation of the intra-rare-earth alloys in the system YYb has been investigated at 0.75, 2.5, 4.0 and 7.7 GPa. It has been found that the alloys synthesized at high pressure crystallize in the sequence of structures h.c.p.-d.h.c.p.-f.c.c. with increasing ytterbium concentration. The magnetic susceptibility of Y1 − xYbx alloys prepared at 7.7 GPa was measured as a function of temperature from 4.2 to 300 K. The concentration dependence of the valence of the ytterbium ions in these alloys has been determined both from lattice parameter measurements and from experimentally measured magnetic susceptibility x by using a relationship between x and the average number of f-electrons derived in the mean-field approximation. Increasing x in the Y1 − xYbx alloys is shown to drive the valence transition first order at 0.3

New phases were detected in alloys of the R-Fe series which were obtained by quenching from the melt at a constant pressure of 7.7 GPa. These compounds have the following imperfect disordered Laves phase structures: MgZn2 type (C14) for R≡Tb, Ho, Er, Tm, Yb, Lu, and MgCu2 type (C15) for R≡Pr, Sm, Dy. The connection between the structures of the new phases and the structure of metallic RFe2 glasses is discussed.

The compounds RNiAl (R ≡ Sm — Lu, Y) with Laves phase structures (C14) were obtained from mixtures of the powdered initial components by annealing at 1450–1500 °C and a pressure of 7.7 GPa.