Magnetism and structural chemistry of ternary borides RE2MB6 (RE = rare earth, M = Ru,Os)

The magnetic behavior of the ternary borides RE₂RuB₆ and RE₂OsB₆ (RE = Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) was studied in the temperature range 1.5 K < T < 1100 K. All compounds crystallize with the Y₂ReB₆-type structure and are characterized by direct RE-RE contacts and the formation of planar infinite two-dimensional rigid boron nets. The magnetic properties reveal a typical Van Vleck paramagnetism of free RE³⁺-ions at temperatures higher than 200 K with ferromagnetic interaction in the low-temperature range T < 55 K. The ferromagnetic ordering temperatures vary with the De Gennes factor. There is no indication for a magnetic contribution from the Ru(Os)-sublattice. Above 1.8 K none of the samples were found to be superconducting.     

Multiple magnetic phase transitions,dilute Fe hyperfine fields and europium valence instabilities in RMn2Si2-xGex,R=rare earth

Mössbauer studies of dilute⁵⁷Fe and¹⁵¹Eu in RMn₂Si_2-xGe_x (R=La, Sm, Eu and Gd) at temperatures 4.2 K to 480 K have been performed. The diamagnetic iron and europium reveal the magnetic order of the Mn and rare earth sublattices through transferred hyperfine interactions. The⁵⁷Fe studies show that in LaMn₂Si₂, LaMn₂Ge₂, and SmMn₂Ge₂ the Mn is magnetically ordered above the known Curie temperatures, and the compounds are antiferromagnets up to T_N=470 K, 415 K and 385 K respectively. Studies of¹⁵¹Eu in R_1-xEu_xMn₂Si₂, (R=La, Gd) display Eu subspectra corresponding to Eu²⁺, Eu³⁺ and intermediate valant Eu. All display large magnetic hyperfine fields.     

Study of the paramagnetic centers in heterofullerides MnM′3-nC60 (M = K, Rb, Cs; M′ = Be, Mg, Ca, Ba; n = 1, 2)

New heterofullerides Cs₂MC₆₀, CsM₂C₆₀, Rb₂MC₆₀, K₂MC₆₀, and KM₂C₆₀ (M = Be, Mg, Ca, Ba) have been synthesized; the temperature dependences of the magnetic susceptibilities of these compounds in the temperature range from 4.2 to 297 K have been measured. Among these heterofullerides, K₂MgC₆₀, KMg₂C₆₀, K₂CaC₆₀, K₂BeC₆₀, and Rb₂BeC₆₀ pass to the superconducting state at temperatures T _c = 13–24.3 K. The paramagnetic electronic states of the compounds have been studied by EPR at temperatures of 105–300 K, which shows the existence of two types of paramagnetic centers, related to oxygen defects and conduction electrons.     

A study of the new cubic,ordered perovskites BaLaMRuO6 (M = Mg,Fe, Co,Ni, or Zn) and the related phases La2MRuO6 (M = Mg,Co, Ni,or Zn) by 99Ru Mössbauer spectroscopy and other techniques

⁵⁷Fe and ⁹⁹Ru Mössbauer spectroscopy, coupled with magnetic susceptibility measurements down to 4.2 K, have been used to study the electronic and magnetic properties of the new cubic-ordered perovskites BaLaMRuO₆ (M = Mg, Fe, Co, Ni, or Zn). The ruthenium is present in the +5 oxidation state in all the compounds except BaLaFeRuO₆ which contains iron(III) and ruthenium(IV). All the compounds exhibit long-range antiferromagnetic order, with Néel temperatures in the range 20–40 K. Mössbauer spectra for the new compound La₂CoRuO₆ and the isostructural cubic perovskites La₂MRuO₆ (M = Mg, Ni, or Zn) confirm the presence of ruthenium(IV) in these phases and indicate that they are not ordered magnetically at 4.2 K.     

Electrical resistivity of pyrochlore compounds R2Mo2O7(R =Nd,Sm, Gd,Tb, Y)

The electrical resistivity ofR₂Mo₂O₇(R =Nd, Sm, Gd, Tb, Y) pyrochlores was measured in the temperature range 4.2 to 300 K. Metallic behavior is observed for Nd₂Mo₂O₇, Sm₂Mo₂O₇, and Gd₂Mo₂O₇ which have relatively high magnetic ordering temperatures due to ferromagnetism on the molybdenum sublattice. A clear drop in resistivity is observed near the magnetic ordering point for all metallic materials. A resistance minimum observed at low temperatures, which may be due to the magnetic ordering of the rare-earth sublattice, is not completely understood. Tb₂Mo₂O₇ and Y₂Mo₂O₇, which show no molybdenum sublattice ordering down to 4.2 K, are semiconductors. However, the temperature dependence of the resistivity is not exponential. This unusual resistivity behavior is typical of degenerate semiconductors.     

New representatives of the Raddlesden-Popper homologous series: Anion-deficient oxides Sr3Co2−x ZnxO6 + δ (x = 0.5, 0.75)

New complex oxides Sr₃Co_2?x Zn_xO_{6 + δ} with x = 0.50 and 0.75, which belong to the Raddlesden-Popper homologous series (A _n+1B_nO_3n+1; n=2), are synthesized. The structural and magnetic properties of these oxides are studied. The unit cell parameters a and c for the x = 0.5 and 0.75 compounds are 0.38541(2) and 0.38573(2) nm and 2.03543(1) and 2.03999(11) nm, respectively. The magnetic susceptibility of Sr₃Co_1.5Zn_0.5O_6.25 as a function of temperature obeys the Curie-Weiss law (x = C/(T ? η)) only within a narrow temperature range from 250 to 300 K. At low temperatures, this compound has spin-glass properties with a characteristic magnetic and temperature hystereses and a freezing temperature of T _g = 25?30 K.     

Crystal and magnetic structures and magnetic properties of selenate containing natrochalcite, A(I)M(II)2(H3O2)(SeO4)2 where A = Na or K and M = Mn, Co, or Ni

The synthesis of a series of selenate containing natrochalcite, A(I)M(II)(2)(H(3)O(2))(SeO(4))(2) where A = Na or K and M = Mn, Co, or Ni (here labeled as AMH and AMD for the hydrogenated and deuterated compounds, respectively), the X-ray crystal structure determinations from single crystals (Ni) and powder (Mn), magnetic properties, and magnetic structures of the cobalt analogues are reported. The nuclear crystal structures for NaNiH, KNiH, and KMnH are similar to those reported for the cobalt analogues (NaCoH and KCoH) and consist of chains of edge-sharing octahedra (MO(6)) which are connected by H(3)O(2) and SeO(4) to form layers which are in turn bridged by the alkali, in an octahedral coordination site, to form the 3D-framework. The magnetic properties are characterized by antiferromagnetic interaction at high temperatures and antiferromagnetic ordering at low temperatures (NaCoH, 3.5 K; KCoH, 5.9 K; KNiH, 8.5 K; and KMnH, 16 K), except for KNi(2)(H(3)O(2))(SeO(4))(2) which displays a weak ferromagnetic interaction and no long-range ordering above 2 K. The neutron magnetic structures of the cobalt analogues, studied as a function of temperature, are different for the two cobalt salts and also different from all the known magnetic structures of the natrochalcite family. Whereas the magnetic structure of NaCoD has a k = (0, 0, 0), that of KCoD has one consisting of a doubled nuclear cell, k = (0, 0, 1/2). Both compounds have four magnetic sublattices related to the four cobalt atoms of the nuclear unit cell. In NaCoD the moments are in the bc-plane, M(y) = 2.51(2) μ(B) and M(z) = 1.29(4) μ(B), with the major component along the cobalt chain and the resultant moment, 2.83(3) μ(B), making an angle of 27° with the b-axis. The sum of the moments within the cell is zero. For KCoD the moment at each cobalt site has a component along each crystallographic axis, M(x) = 2.40(3), M(y) = 1.03(3), M(z) = 1.59(8) giving a total M = 2.49(3) μ(B). Within one nuclear cell the moments are fully compensated. The moments corresponding to the cobalt atoms of the second nuclear cell comprising the magnetic unit cell are oriented in opposite directions.     

Magnetische Eigenschaften der Verbindungsreihe EuBX mit B = Element der ersten Neben- und X = Element der fünften Hauptgruppe

Magnetic Properties of the Compound Series EuBX with B = Element of the First Subgroup and X = Element of the Fifth Main Group The magnetic properties of the compounds EuBX (B ? Cu, Ag, Au; X ? P, As, Sb, Bi) in the temperature range between 3.8 and 300 K are reported. These compounds crystallize in a modified Ni₂In-type structure. The compounds EuCuP, EuAgP, EuAuP, and EuAuAs show at low temperatures ferromagnetic behaviour, EuCuAs and EuAgAs are metamagnetic. According to our measurements this seems to be the same with EuCuSb, EuAgSb, EuAuSb, and EuAuBi whereas EuCuBi and EuAgBi show antiferromagnetic interaction.     

Syntheses, structure, and selected physical properties of CsLnMnSe3 (Ln = Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y) and AYbZnQ3 (A = Rb, Cs; Q = S, Se, Te)

CsLnMnSe(3) (Ln = Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y) and AYbZnQ(3) (A = Rb, Cs; Q = S, Se, Te) have been synthesized from solid-state reactions at temperatures in excess 1173 K. These isostructural materials crystallize in the layered KZrCuS(3) structure type in the orthorhombic space group Cmcm. The structure is composed of LnQ(6) octahedra and MQ(4) tetrahedra that share edges to form [LnMQ(3)] layers. These layers stack perpendicular to [010] and are separated by layers of face- and edge-sharing AQ(8) bicapped trigonal prisms. There are no Q-Q bonds in the structure of the ALnMQ(3) compounds so the formal oxidation states of A/Ln/M/Q are 1+/3+/2+/2-. The CsLnMnSe(3) materials, with the exception of CsYbMnSe(3), are Curie-Weiss paramagnets between 5 and 300 K. The magnetic susceptibility data for CsYbZnS(3), RbYbZnSe(3), and CsYbMSe(3) (M = Mn, Zn) show a weak cusp at approximately 10 K and pronounced differences between field-cooled and zero-field-cooled data. However, CsYbZnSe(3) is not an antiferromagnet because a neutron diffraction study indicates that CsYbZnSe(3) shows neither long-range magnetic ordering nor a phase change between 4 and 295 K. Nor is the compound a spin glass because the transition at 10 K does not depend on ac frequency. The optical band gaps of the (010) and (001) crystal faces for CsYbMnSe(3) are 1.60 and 1.59 eV, respectively; the optical band of the (010) crystal faces for CsYbZnS(3) and RbYbZnSe(3) are 2.61 and 2.07 eV, respectively.     

Structures, magnetic, and thermal properties of Ln3MoO7 (Ln=La, Pr, Nd, Sm, and Eu)

Ternary lanthanide-molybdenum oxides Ln₃MoO₇ (Ln=La, Pr, Nd, Sm, Eu) have been prepared. Their structures were determined by X-ray diffraction measurements. They crystallize in a superstructure of cubic fluorite and the space group is P2₁2₁2₁. The Mo ion is octahedrally coordinated by six oxygens and the slightly distorted octahedra share corners forming a zig-zag chain parallel to the b-axis. These compounds have been characterized by magnetic susceptibility and specific heat measurements. The La₃MoO₇ shows complex magnetic behavior at 150 and 380 K. Below these temperatures, there is a large difference in the temperature-dependence of the magnetic susceptibility measured under zero-field-cooled condition and under field-cooled condition. The Nd₃MoO₇ show a clear antiferromagnetic transition at 2.5 K. From the susceptibility measurements, both Pr₃MoO₇ and Sm₃MoO₇ show the existence of magnetic anomaly at 8.0 and 2.5 K, respectively. The results of the specific heat measurements also show anomalies at the corresponding magnetic transition temperatures. The differential scanning calorimetry measurements indicate that two phase-transitions occur for any Ln₃MoO₇ compound in the temperature range between 370 and 710 K.     

Preparation,Crystallographic, Spectroscopic and Magnetic Characterization of Low‐Valency Nitridometalates Li2[(Li1‐xMx)N] with M = Cu,Ni

Thermogravimetric and difference thermal analyses show that the reactions of lithium nitride with the transition metals Cu and Ni under molecular nitrogen to form phases Li₂[(Li_1‐xM^I_x)N] take place above 673 K. The maximum weight gains are reached at 926 K and 968 K for M = Cu and Ni, respectively. At higher temperatures, the ternary phases Li₂[(Li_1‐xM^I_x)N] decompose, limiting the substitutional level x. In the temperature range of 773 K — 873 K, the successful synthesis of Li₂[(Li_1‐xNi^I_x)N] (0 < x ≤ 0.85(1)) single phase products is demonstrated. Maximum substitution obtained for the Cu phases is x_max= 0.43(1). The dependence of the lattice parameters of the hexagonal unit cell on x is almost linear. The magnetic moment of M strongly depends on x. At low x the magnetic moments in phases with M = Ni are presumably enhanced by orbital effects. A decrease of μ_eff with x to μ_eff(x = 1) → 0 is explained by delocalization of the magnetic moments and by the gradual formation of a metal for the hypothetical compound Li₂[NiN] (x = 1). XAS spectroscopy at the transition metal K‐edges shows that Cu and Ni principally correspond to d¹⁰‐ and d⁹‐configurations, respectively.     

Metal-insulator transition of charge-transfer salts based on unsymmetrical donor DMET and metal halide anions (DMET)4(MCl4)(TCE)2 (M = Mn, Co, Cu, Zn; TCE = 1,1,2-trichloroethane)

New charge-transfer salts based on an unsymmetrical donor DMET [dimethyl(ethylenedithio)diselenadithiafulvalene] and metal halide anions (DMET)4MIICl4(TCE)2 (M = Mn, Co, Cu, Zn; TCE = 1,1,2-trichloroethane) have been synthesized and characterized by transport and magnetic measurements. The crystal structures of the DMET salts are isostructural, consisting of a quasi-one-dimensional stack of DMET and insulating layers containing metal halide anions and TCE. Semimetallic band structures are calculated by the tight-binding approximation. Metal-insulator transitions are observed at TMI = 25, 15, 5-20, and 13 K for M = Mn, Co, Cu, and Zn, respectively. The M = Cu salt exhibits anisotropic conduction at ambient pressure, being semiconducting in the intralayer current direction but metallic for the interplane current direction, down to T(MI). The metal-insulator transitions are suppressed under pressure. In the M = Co and Zn salts, large magnetoresistances with hysteresis are observed at low temperatures, on which Shubnikov-de Haas oscillations are superposed above 30 T. In the M = Cu salt, no hysteresis is observed but clear Shubnikov-de Haas oscillations are observed. The magnetoresistance is small and monotonic in the M = Mn salt. Paramagnetic susceptibilities of the spins of the magnetic ions are observed for the M = Mn, Co, and Cu salts with small negative Weiss temperatures of approximately 1 K. In the nonmagnetic M = Zn salt, Pauli-like pi-electron susceptibility that vanishes at TMI is observed. The ground state of the pi-electron system is understood as being a spin density wave state caused by imperfect nesting of the Fermi surfaces. In this pi-electron system, the magnetic ions of the M = Mn, Co, and Cu salts interact differently, exhibiting a variety of transport behaviors.     

Stoichiometry and physical properties of ternary molybdenum chalcogenides MxMo6X8 (X = S,Se; M = Li,Sn, Pb)

Chemical and electrochemical insertion of Li at room temperature, as well as insertion of lead and tin at moderate temperatures (500°C), into the binary phase Mo₆X₈ forms ternary molybdenum chalcogenides M_xMo₆X₈ (X = S, Se). Crystallographic parameters, superconducting properties, and magnetic susceptibility are reported. The stoichiometry x for lead and tin is shown not to exceed x = 1, while for Li, x can reach approximately 4.0. For the lead and tin sulfide series, the hexagonal lattice parameters and superconducting critical temperatures (T_c) are invariant to changes in the nominal composition of 0.8 < x < 1.2, while both an increase in T_c and a small decrease in c_h is observed for the selenides; a narrow homogeneity range exists near x = 1 below 500°C for both these sulfides and selenides, the single-phase region being somewhat larger in the selenides. In contrast, several single-phase regions and large unit cell changes are observed in Li_xMo₆X₈ (0 < x < 3.2). Magnetic susceptibility measurements of the lithiated compounds at x ～ 3.2 reveals a structural phase transition at 140 and 185 K for the sulfide and selenide, respectively; but neither superconducts down to 1.5 K. At lower lithium concentration near x ～ 1.0, the T_c of the sulfide is raised from that of Mo₆S₈ (1.8 K) to 5.2 K but the T_c of Mo₆Se₈ (6.5 K) is depressed to 3.9 K.     

Magnetoelectronic properties of ferromagnetic compounds Rb2TaZ6 (Z = Cl,Br) for possible spintronic applications

Highly spin-polarized ferromagnetic materials are essential for efficient spintronic devices. Here, 100% spin-polarized compounds Rb₂TaZ₆ (Z = Cl, Br) studied via density functional theory are reported. These compounds show stability in the ferromagnetic phase with cubic symmetry and half metallic behavior, thereby exhibiting a nonzero direct band gap in the spin-down channel and zero band gap in the spin-up configuration. The Ta-d sates contribute mainly to the net magnetic moments as explained by the crystal field theory and density of states. High Curie temperatures of 960.35 and 1021.74 K for Ra₂TaCl₆ and Rb₂TaBr₆, along with maximum spin polarizability, make these compounds favorable for efficient spintronic applications.     

Die Gadoliniumcarbidhalogenide Gd4C2X3 (X = Cl,Br)

The Gadolinium Carbide Halides, Gd₄C₂X₃ (X = Cl, Br) The compounds Gd₄C₂X₃ (X = Cl, Br) and Tb₄C₂Br₃ have been prepared by reaction of the metals (RE), REX₃, and C in sealed Ta capsules at 1 100° and 1 300°C, respectively. Monophasic samples of Gd₄C₂Br₃ and Tb₄C₂Br₃ were obtained by reacting stoichiometric mixtures of the starting materials for five days. The needle shaped crystals are bronze-coloured and sensitive to air and moisture. Gd₄C₂X₃ crystallizes in the space group Pnma (No. 62) with lattice constants a = 1 059.6(4), b = 368.4(1), c = 1 962.7(8) pm (Gd₄C₂Cl₃), a = 1 084.4(1), b = 373.0(1), c = 2 036.1(1) pm (Gd₄C₂Br₃). According to Guinier photographs, Tb₄C₂Br₃ is isotypic (a = 1 074.3(2), b = 370.6(1), c = 2 019.4(1) pm). In the crystal structure C is octahedrally coordinated by Gd. The Gd₆ octahedra are linked via common edges to form corrugated layers. The X-anions coordinate all free edges and corners of these layers and connect them via Xⁱ? Xⁱ contacts parallel [001]. Gd₄C₂Br₃ shows metallic conductivity. The magnetic susceptibility follows at high temperatures a Curie Weiss law with an effective moment of 7.95 μ_B. At temperatures below 50 K antiferromagnetic order is observed.     

EuAuGe Type Indides RAgIn (R = Ca,Sr, La,Eu)

The equiatomic intermetallic phases CaAgIn [a = 482.75(7), b = 750.0(1), c = 835.5(1) pm], SrAgIn [a = 495.86(5), b = 794.71(9), c = 851.89(9) pm], LaAgIn [a = 489.99(5), b = 767.93(9), c = 837.53(9) pm], and EuAgIn [a = 493.02(7), b = 781.6(1), c = 844.2(1) pm] were synthesized from the elements in sealed niobum containers. They crystallize with the EuAuGe type structure, space group Imm2. The four structures were refined from single‐crystal X‐ray data. The silver and indium atoms build up orthorhombically distorted, puckered Ag₃In₃ hexagons, which are stacked in AA′ sequence, leading to direct Ag–Ag and In–In interlayer bonding (e.g. 303 and 304 pm in CaAgIn). Temperature dependent magnetic susceptibility measurements show a magnetic moment of 7.40(1) μ_B per europium atom. EuAgIn orders antiferromagnetically at 5.7(5) K. The divalent nature of europium is also evident from ¹⁵¹Eu Mössbauer spectra: δ = –10.50(1) mm · s^–1 at 78 K.     

Magnetic and calorimetric studies on rare-earth iron borates LnFe3(BO3)4 (Ln=Y, La-Nd, Sm-Ho)

A series of rare-earth iron borates having general formula LnFe₃(BO₃)₄ (Ln=Y, La-Nd, Sm-Ho) were prepared and their magnetic properties have been investigated by the magnetic susceptibility, specific heat, and ⁵⁷Fe Mössbauer spectrum measurements. These borates show antiferromagnetic transitions at low temperatures and their magnetic transition temperatures increase with decreasing Ln³⁺ ionic radius from 22 K for LaFe₃(BO₃)₄ to 40 K for TbFe₃(BO₃)₄. In addition, X-ray diffraction, specific heat, and differential thermal analysis (DTA) measurements indicate that the phase transition occurs for the LnFe₃(BO₃)₄ compounds with Ln=Eu-Ho, Y, and its transition temperature increases remarkably with decreasing Ln³⁺ ionic radius from 88 K for Ln=Eu to 445 K for Ln=Y.     

Etude par effet Mössbauer des composés de type “bronzes fluorés” MxFeF3 (M = K,Rb, Cs,NH4)

The hexagonal, tetragonal and pyrochlore-type nonstoichiometric iron fluorides M_xFeF₃ (M = K, Rb, Cs, NH₄) have been studied by Mössbauer spectroscopy over the temperature range 4.2 to 295 K. The magnetic transition temperatures have been determined. The ferrous and ferric ions remain in discrete oxidation states indicating the absence of charge hopping. The broadened lines of the spectra of the hexagonal and tetragonal phases are consistent with the disordering of Fe²⁺ and Fe³⁺ in the structure. By contrast, the narrow linewidths of the spectra of the pyrochlore-type phases characterize a structural ordering between the ferrous and ferric ions.     

Three Novel Rare-earth Complexes with Nitronyl Nitroxide Radical [RE(hfac)3 (NITPhOCH3)2] [RE = GdIII, YIII and ErIII]: Syntheses, Crystal Structures and Magnetic Properties

Three novel isomorphous complexes of formula [RE(hfac)₃(NITPhOCH₃)₂], where RE = Gd^III, Y^III and Er^III; hfac = hexafluoroacetylacetonate; NITPhOCH₃ = 4′-methoxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, were synthesized, structurally and magnetically characterized. The crystal structure consists of isolated molecules where the nitronyl nitroxide radicals act as monodentate ligands towards RE(III) through the oxygen atom of the N–O group. The magnetic properties of the complexes were studied by measuring their magnetic susceptibilities at various temperatures in the 5–300 K range. The analyses of these magnetic measurements showed that the spin coupling between the gadolinium ion and the radicals in the Gd^III complex is ferromagnetic, while antiferromagnetic superexchange interaction exists between the two radicals in the Gd^III and Y^III complexes. The Er^III complex reveals an overall intramolecular antiferromagnetic exchange interaction.     

Etude comparative des propriétés cristallographiques,diélectriques et d'optique non linéaire des phases ABCNb5O15 (A = Ca,Sr, Ba,B = Ca,Sr, Ba,C = Na,K) de type “bronzes oxygénés de tungstène quadratiques”

The crystallographic, dielectric and nonlinear optic properties of the ABCNb₅O₁₅ phases (A = Ca, Sr, Ba; B = Ca, Sr, Ba; C = Na, K) are compared. Nine alkali-alkaline earth niobates, of which three are new, with tetragonal bronze-like structure, have been isolated; symmetry and parameters are determined. All are ferroelectric, the Curie temperatures are measured. Four phases have been shown to be potentially good materials for the harmonic generation of 0.53 μ radiation. The optical yield increases with rising Curie temperature.