Low binding energy satellites in the 3d X-ray photoelectron spectra of rare earths (R) in RMn2Si2 and RGa2

The 3_d core-level X-ray photoelectron spectra of rare earths (R) in RMn₂Si₂ (R = Pr, Nd, Sm, Gd) and RGa₂ (R = Pr, Nd, Sm) have been recorded. A structure has been detected on the low binding energy side of each of the 3d_{$\text{5}\text{2}$} and 3d_{$\text{3}\text{2}$} photoemission peaks. The structure identified as a shake-down satellite shows no chemical shift. The energy separation of the satellite has been measured with respect to the main 3d_{$\text{5}\text{2}$} peak. The present results have been examined in the light of recent experimental and theoretical reports.     

Magnetic properties of R3Co29Si4B10 (R=La, Ce, Pr, Nd, Sm, Gd and Dy) borides

The crystal structure and magnetic properties of quaternary rare-earth intermetallic borides R₃Co₂₉Si₄B₁₀ with R=La, Ce, Pr, Nd, Sm, Gd and Dy have been studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in a tetragonal crystal structure with the space group P4/nmm. Compounds with R=La, Ce, Pr, Nd and Sm are ferromagnets, while ferrimagnetic behavior is observed for R=Gd and Dy. The Curie temperatures vary between 149 K and 210 K. The Curie temperatures in R₃Co₂₉Si₄B₁₀ (R=Ce, Pr, Nd, Sm, Gd, Dy) compounds are roughly proportional to the de Gennes factors.     

Magnetic phase transition and the corresponding magnetostriction of intermetallic compounds RMnsGe2（R=Sm,Gd）

The temperature dependence of lattice constants a and c of intermetallic compounds RMn₂Ge₂ (R=Sm, Gd) is measured in the temperature range 10－800K by using the x-ray diffraction method. The magnetoelastic anomalies of lattice constants are found at the different kinds of spontaneous magnetic transitions. The transversal and longitudinal magnetostrictions of polycrystalline samples are measured in the pulse magnetic field up to 25T. In the external magnetic field there occurs a first-order field-induced antiferromagnetism－ferromagnetism transition in the Mn sublattice, which gives rise to a large magnetostriction. The magnitude of magnetostrictions is as large as 10^-3. The transversal and longitudinal magnetostrictions have the same sign and are almost equal. This indicates that the magnetostriction is isotropic and mainly caused by the interlayer Mn－Mn exchange interaction. The experimental results are explained in the framework of a two-sublattice ferrimagnet with the negative exchange interaction in one of the sublattices by taking into account the lattice constant dependence of interlayer Mn－Mn exchange interaction.     

A non-magnetic Fe probe of multiple magnetic phase transitions in RMn2Si2−x Ge x,R=rare earth

Summary Dilute⁵⁷Fe M?ssbauer-spectroscopy studies of RMn₂X₂ (X=Si and/or Ge, R=La, Ce, Pr, Nd, Sm, Eu and Gd) at 4.2 to 650 K yield the following results: Fe in RMn₂X₂ does not carry a magnetic moment. It reveals the magnetic order in the Mn and R sublattices through transferred hyperfine fields (∼100 kOe). The compounds LaMn₂Si₂, LaMn₂Ge₂, CeMn₂Ge₂, PrMn₂Ge₂, NdMn₂Ge₂ and SmMn₂Ge₂, known to be ferromagnets withT _c=300–350 K, are antiferromagnetically ordered above their correspondingT _c. TherT _N values extend from 385 K (SmMn₂Ge₂) to 470 K (LaMn₂Si₂). At the ferromagnetic-antiferromagnetic phase transition, a sharp reorientation of the Mn magnetic moments relative to the crystalline axes occurs. In RMn₂Si_2−x Ge _x with intermediatex values, the Ge is much more dominant in determining the magnetic properties of the Mn sublattice. While PrMn₂Si₂ is an antiferromagnet (T _N=365 K) and PrMn₂Ge₂ is a ferromagnetantiferromagnet (T _c=328 K,T _N=415 K), we find that in PrMn₂SiGe, the magnetic behaviour is similar to that in pure PrMn₂Ge₂,T _c=305 K andT _N=395 K. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

金属间化合物RMn2Ge2(R=La,Pr,Nd,Sm,Gd,Tb和Y)中的自发磁相变 及相变时的磁弹性异常

在10—800K的温度范围内用X射线衍射方法测量了RMn₂Ge₂(R=La,Pr ,Nd,Sm,Gd,Tb和Y)的晶格常数与温度的变化关系.在各种类型的自发磁相变观察到晶格常数 的磁弹性异常现象.实验得出,自发磁相变时的磁弹性异常主要由Mn次晶格引起,并且Mn-Mn 交换相互作用能不仅与晶格常数a有关,而且与晶格常数c有关.用Kittle的交换反转模型讨 论了低温时的铁磁—反铁磁一阶相变. 关键词： 稀土金属间化合物 磁相变 磁弹性     

X-ray studies of magnetic phase transitions in the intermetallic compounds RMn2Ge2 (R=La, Sm, Gd, Nd, Tb, and Y)

The lattice parameters a and c of the tetragonal intermetallic compounds RMn₂Ge₂ (R=La, Sm, Gd, Nd, Tb, and Y) have been measured by x-ray diffraction in the temperature interval 10–800 K. Anomalies are observed in the temperature dependence of a and c due to phase transitions from the paramagnetic to the magnetically ordered state in the Mn subsystem, transitions between various magnetically ordered phases due to a change in the magnitude and sign of the Mn-Mn exchange interaction, and magnetic transitions caused by ordering of the rare-earth subsystem leading to a rearrangement of the magnetic structure of the Mn subsystem. It is concluded that, along with the lattice parameter a, the lattice parameter c also has an influence on the Mn-Mn exchange interaction. Fiz. Tverd. Tela (St. Petersburg) 41, 2053–2058 (November 1999)     

Magnetic ordering in rare earth iron silicides and germanides of the RFe2X2 type

Rare earth iron silicides and germanides of the RFe₂Si₂ or RFe₂Ge₂ type with R = La, Ce, Pr, Nd, Sm, Gd and Dy were measured for their magnetic susceptibility. The silicides and germanides of Nd and Gd are antiferromagnetically ordered below a Neel point of, respectively, 11 and 7°K for the silicides and 13 and 11 for the germanides. The Nd sublattice under-goes a spin-flop transition which at 4.2°K is at 11 KOe. Although the Fe sublattice is diamagnetic, all the samples showed a weak ferromagnetic ordering below a temperature of about 700°K. The ratio between the dia- and ferromagnetic phases is 94:6 per cent in the silicides and 80:20 in the germanides, as determined by Mössbauer spectroscopy and supported by magnetization measurements.     

Magnetic properties of ternary RMn2Si2 and RMn2Ge2 compounds

Magnetic properties of RMn₂Si₂ and RMn₂Ge₂ compounds, where R is a rare earth metal, have been investigated by magnetometric measurements. RMn₂Ge₂ (where R is a light rare earth) and LaMn₂Si₂ are ferromagnets. Remaining compounds have antiferromagnetic properties. DyMn₂Si₂ and ErMn₂Si₂ show ferromagnetic properties at low temperatures. It was confirmed that the value of Curie (or Néel) temperature for the Mn sublattice decreases with increasing c constant.     

Magnetic properties and hyperfine interactions in RCo2B2 (R = Nd,Gd, Tb)

The magnetic properties of RCo₂B₂ compounds which crystallize in the ThCr₂Si₂ structure with R = Nd, Gd, Tb have been investigated. The magnetic structure is ferromagnetic for NdCo₂B₂ and GdCo₂B₂, T_c equals 32 and 26 K respectively and antiferromagnetic for TbCo₂B₂ (T_N = 19 K). Curie-Weiss behaviour is exhibited by all the compounds and the effective moments derived indicate that Co is diamagnetic. The difference in magnetic properties between RCo₂B₂ and other isomorphous RCo₂X₂ (X = Si, Ge) is discussed. Mössbauer studies of ¹⁵⁵Gd in GdCo₂B₂ yielded the hyperfine interaction parameters and determined the direction of the magnetization to be in the basal plane. The electric quadropole interaction at 4.1 K is 580 MHz sec^?1, this is the largest ever found in an intermetallic Gd containing compound.     

Pressure-induced transition in a heavy fermion YbPd2Si2

We report the results of a room-temperature investigation of the thermoelectric and the dilatometric properties of a heavy fermion system YbPd₂Si₂ (itterbium-palladium-silicon, 1-2-2) at high pressure P up to 22 GPa; YbPd₂Si₂ is a less-studied representative of the RM₂X₂ family (R=Ce, Yb, U; M=transition metal; X=Si, Ge) with the tetragonal ThCr₂Si₂-type structure of the I4/mmm space group. Around P∼6±0.5 GPa, a phase transition in Yb-Pd-Si was registered by the drastic changes in the pressure dependencies of the electrical resistance R, the thermopower (Seebeck effect) S, a temperature difference along a sample ΔT, and a sample's thickness Δx (related to compressibility). Both a nature of the found phase transition and a presumable P-T phase diagram of YbPd₂Si₂ are discussed.     

Effect of Fe-substitution on microstructure, hysteresis behaviour and magnetocaloric effect in Gd5Si2Ge2 Alloys

Effect of Fe-substitution on the phase formation, partitioning behaviour of Fe in the co-existing phases, magneto-structural transition, magnetic entropy change and associated hysteresis losses has been investigated in Gd₅Si₂Ge₂ alloy. The virgin alloy crystallizes in monoclinic Gd₅Si₂Ge₂-type phase, while Fe-substituted alloys form mixed monoclinic Gd₅Si₂Ge₂-type and orthorhombic Gd₅Si₄-type phases. Electron probe microanalysis reveals that Fe does not dissolve in the matrix, but influences the magneto-structural transitions. Magneto-structural characterization of the Fe-containing alloys reveals that the Fe-substitution suppresses the structural transition observed at 273 K in virgin alloy. A maximum magnetic entropy change, ΔS_M of 6.5 J/kg-K at 273 K was observed for a field change of 2 T in Gd₅Si₂Ge₂ alloy. The Fe-substituted alloys exhibit lower value of ΔS_M but with reduced hysteresis losses.     

Magnetic and magneto-lattice dynamics in GdMn<Subscript>2</Subscript>O<Subscript>5</Subscript>

The dynamics of magnetoelectric RMn₂O₅ crystals (R=Eu and Gd) was studied in the frequency and temperature ranges 20–300 GHz and 5–50 K, respectively. The crystals possessed magnetic and ferroelectric long-range order and had close transition temperatures, T_{N, C}?36 and 30 K for R=Eu and Gd, respectively. Mixed magneto-lattice excitations were observed in GdMn₂O₅; the excitations were most intense near the transition temperature T?30 K at frequencies close to the antiferromagnetic resonance frequencies of the Mn subsystem. Along with the antiferromagnetic resonance of the Mn subsystem, the ferromagnetic resonance of the Gd subsystem was observed in GdMn₂O₅ in an external magnetic field. No such dynamics was characteristic of EuMn₂O₅.     

The119Sn Mössbauer effect in RMn6Sn6 compounds (R=Gd,Y)

The magnetic properties of intermetallic compounds RMn₆Sn₆ (T=Gd and Y) have been investigated by¹¹⁹Sn Mössbauer effect measurements. The differences of the hyperfine field on both the Sn₁ and Sn₃ sites were small between GdMn₆Sn₆ and YMn₆Sn₆, while the Mn sublattice orders ferromagnetically for R=Gd and antiferromagnetically for R=Y. This result indicated that Mn moments order antiferromagnetically in the intra-plane of the Kagomè net in YMn₆Sn₆.     

EXAFS study of the local Gd environment in the magnetic superconductor (La1−xGdx)Os2

The near-neighbor environment of Gd in the pseudobinary compound La_1?xGd_xOs₂ has been investigated by studying the EXAFS on the Gd LIII, La LII, and Os LIII edges. For Gd concentrations of x = 0.07 and x = 0.14, we find that the Gd predominantly substitutes on the La sites in the LaOs₂ lattice rather than forming local Gd metal or GdOs₂ clusters. These results are discussed in view of the fact that La_1?xGd_xOs₂ shows spin-glass-like properties (x ≤ 0.15) in the superconducting phase.     

Ferromagnetic rare-earth and diamagnetic iron sublattices in ternary RFe0.67Ge1.33 type compounds

The magnetic properties of RM_2?xSi_x and RM_2?xGe_x where R = La, Ce, Nd, Sm, Eu and Gd and M = Fe, Co, Ni and Ag have been measured. It has been found that for samples of x = 0.4 both R and M sublattices are paramagnetically above 4.2δ K in the high spin state, whereas, if x = 0.67, R is magnetically ordered whereas M is diamagnetic.     

Local structure of multiferroic RMn2O5: Important role of the R site

The temperature and magnetic field dependent local structure of RMn₂O₅ systems was examined. While no significant displacements of the Mn ions are observed, it is found that the R-O distribution exhibits changes at low temperature which are possibly related to the changes in the electric polarization. Density functional computations are used to explore the system dynamics and to link the local structural measurements with anomalous changes in the infrared absorption spectra. The anomalous R-O distribution and observed coupling to magnetic fields point to the need to properly treat the 4f electrons on the R sites in these systems.     

Magnetic phase transitions in layered intermetallic compounds

Magnetic, magnetoelastic, and magnetotransport properties have been studied for the RMn₂Si₂ and RMn₆Sn₆ (R is a rare earth metal) intermetallic compounds with natural layered structure. The compounds exhibit wide variety of magnetic structures and magnetic phase transitions. Substitution of different R atoms allows us to modify the interatomic distances and interlayer exchange interactions thus providing the transition from antiferromagnetic to ferromagnetic state. Near the boundary of this transition the magnetic structures are very sensitive to the external field, temperature and pressure. The field-induced transitions are accompanied by considerable change in the sample size and resistivity. It has been shown that various magnetic structures and magnetic phase transitions observed in the layered compounds arise as a result of competition of the Mn–Mn and Mn–R exchange interactions.     

Magnetism and structural chemistry of ternary silicides: (RE,Th, U)Pt2Si2 (RE = rare earth)

Ternary silicides (RE, U, Th)Pt₂Si₂ have been prepared from the elements. All the compounds (RE= Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and U, Th) were found to be isotypic and crystallize with the primitive tetragonal CePt₂Si₂-type structure closely related to the CaBe₂Ge₂-type. The magnetic properties of these alloys were studied in the temperature range 1.5 K < T < 1100 K and in fields up to 1.3 T revealing a typical Van Vleck paramagnetism of free RE³⁺-ions for temperatures T > 200 K. A nonmagnetic ground state is reflected from the magnetic susceptibility data of CePt₂Si₂, which are interpreted in terms of interconfiguration fluctuations (ICF). The magnetic results of SmPt₂Si₂ (μ_eff = 0.7 BM) compare well with the ideal Van Vleck behavior of Sm₃₊ ions with a $\text{J =}\text{5}\text{2}$ ground state and a low-lying excited first level $\text{J =}\text{7}\text{2}$. At temperatures below 40 K antiferromagnetic ordering is found for (Gd, Tb, U)Pt₂Si₂; whereas in case of (Dy, Ho, Er, Tm)Pt₂Si₂ the onset of ferromagnetism is indicated below 4 K. None of the samples exhibited a superconducting transition above 1.8 K.     

Magnetic and quadrupole interaction studies at 111Cd in GdMn2 and TbMn2

The temperature dependence of the electric quadrupole interaction and the magnetic hyperfine field at ¹¹¹Cd probe sites in RMn₂ (R=Gd, Tb) has been studied by TDPAC method. In the paramagnetic region the quadrupole interaction frequency ν_Q in both compounds varies linearly with temperature. Below the Neel temperature, we find an abrupt decrease in the magnitude of ν_Q which is consistent with an expansion of the unit cell. As an important feature, the data near T_N shows the coexistence of localized and itinerant magnetism of Mn atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Elastooptic effect and sources of the spontaneous birefringence in Gd2(MoO4)3

It is shown that a shear stress applied to support the spontaneous shear in improper ferroelectric Gd₂(MoO₄)₃(GMO) reduces the birefringence Δn'₁₂ measured when viewing along the c-axis. The elastooptic coefficient p₆₆^E in the paraelectric phase has been determined including sign. Using these and known electrooptical data, the soft mode, electrooptic and elastooptic contributions to Δn′₁₂ of GMO are evaluated. The two latter contributions have opposite sign to that of the soft mode which plays a prevailing role.