Simple rules for the understanding of Heusler compounds

A review is given of the physical properties, composition and crystal structure of intermetallic compounds formed between rare-earth elements and non-magnetic metals, with emphasis on the magnetic properties. Included are the properties of compounds in which the non-rare-earth component is a 4d or 5d transition element. Special consideration is given to the properties of pseudo-binary compounds. Results of magnetisation measurements, neutron diffraction and neutron scattering are discussed together with results derived from NMR, ESR and Mossbauer effect spectroscopy. An evaluation is given of the relevance of the experimental results with respect to different types of exchange interactions in this class of intermetallics. Special consideration is also given to the influence of crystal field effects on the magnetic properties and, furthermore, to the occurrence of intermediate valences in several of the compounds of Ce, Sm, Eu and Yb.

https://iopscience.iop.org/article/10.1088/0034-4885/42/8/003/pdf

Intermetallic compounds of rare earths and non-magnetic metals

Superconductivity and ferromagnetic ordering are two antagonistic types of ordering, and their mutual influence leads to many interesting phenomena which have been studied recently in ternary compounds. Theoretical analysis of ferromagnetic materials which are type II superconductors near the superconducting transition point T cl shows that they become type I near the magnetic transition point T M. The proposed theory constructed for the case T M « T cl predicts the formation of a transverse domain-like (DS phase) magnetic structure below T M. The electronic spectrum appears to be gapless in the DS phase of clean compounds with a re-entrant transition. The change from type II to type I behaviour as the sample is cooled to T M has been observed in ErRh4B4. Experimental data for HoMo6S8, HoMo6Se8 and ErRh4B4 give evidence for the coexistence of super-conductivity and non-uniform magnetic ordering below T M. Mutual influence of superconducting and magnetic orderings is also studied.

Coexistence of superconductivity and magnetism theoretical predictions and experimental results

A comprehensive review of structure work on high-Tc oxides as reported during the years 1987 and 1988 is given. Thirteen structures are refined from X-ray single-crystal and/or neutron powder diffraction data:I. (Ba1−x,Kx)BiO3 (Tc=30 K),II. (La2−x, Srx)CuO4 (Tc=40 K),III. (Nd, Ce, Sr)2CuO4 (Tc=28 K),IV. (Nd2−x, Cex)CuO4 (Tc=24 K),V. YBa2Cu3O7 (Tc=90 K),VI. YBa2Cu4O8 (Tc=80 K),VII. Y2Ba4Cu7O14 (Tc=40 K),VIII. Pb2Sr2NdCu3O8 (Tc=70 K),IX. TlBa2CaCu2O7 (Tc=103 K),X. TlBa2Ca2Cu3O9 (Tc=120 K),XI. Tl2Ba2CuO6 (Tc=90 K),XII. Tl2Ba2CaCu2O8 (Tc=112 K),XIII. Tl2Ba2Ca2Cu3O10 (Tc=125 K). Except forI (perovskite type),II (K2NiF4 type) andIV (Nd2CuO4 type) they represent new structure types. Structure data, bond distances, structure drawings and calculated X-ray powder diffraction patterns are given for each compound. Structural features and correlations with superconductivity are discussed. The review contains 301 citations.

Crystal structures of high- T c oxides

Unlike YBa2Cu3O7−δ (Y123), the Nd-Ba-Cu-O system exhibits a solid solution, Nd1+xBa2−xCu3O7+δ (Nd123ss), for 0.04⩽x⩽0.6. However, the superconducting properties decrease nonlinearly for increasing x, and Tc can also be varied by lowering the annealing temperature without changing the low-temperature oxygen soak. The changes in microstructure and Tc with increasing x are analogous with Y123 with increasing δ, yet for fully oxygenated Nd123ss samples, electron energy loss spectroscopy (EELS) demonstrates that the total unoccupied density of states below the unfilled band is constant for all x. The neutron diffraction and the inert gas fusion analysis support an overall charge balance for all x. Tc is modeled in terms of a forced oxygen disorder resulting from Nd3+ atoms on the Ba sites relocating chain oxygens to anti-chain sites. The variability in Tc as a function of x and heat treatments can be explained by the number of four-fold coordinated Cu's on the chains which can be varied by differing the amounts of paired and unpaired Nd3+ substituting for Ba2+, resulting in more or less charge transfer from the planes to the chains.

Hole filling, charge transfer and superconductivity in Nd1+xBa2−xCu3O7+δ

Electronic and magnetic properties of rare-earth ions in REBa2Cu3O7−x (RE=Dy, Ho, Er)

The magnetic and superconducting properties of the Heusler alloy ${\mathrm{Pd}}_{2}$YbSn have been investigated with heat-capacity, resistivity, and magnetic-susceptibility measurements. The material undergoes a superconducting transition at 2.46 K and a magnetic transition at 0.23 K. The absence of reentrant behavior shows that the magnetically ordered state is coexistent with the superconductivity. A combined analysis of all the data gives the cubic crystalline electric-field parameters W=-12 K and x=-0.65, implying that the ground state of the ${\mathrm{Yb}}^{3+}$ ion in ${\mathrm{Pd}}_{2}$YbSn is a ${\ensuremath{\Gamma}}_{7}$ magnetic doublet.

Coexistence of ordered magnetism and superconductivity in Pd 2 YbSn

The magnetic properties of the neptunium monopnictides, NpN, NpP, NpAs, and NpSb, have been examined by a variety of experimental techniques. All compounds have the NaCl structure. The present paper reports the results of magnetization, M\"ossbauer, electrical-resistivity, neutron-diffraction, and lattice-parameter (x-ray) measurements between 1.5 and 300 \ifmmode^\circ\else\textdegree\fi{}K on polycrystalline samples prepared in this laboratory. Particular emphasis is placed on both the complementary information obtained by the different techniques, and how this helps to elucidate the microscopic magnetic behavior. Neptunium nitride is ferromagnetic with ${T}_{C}=87$ \ifmmode^\circ\else\textdegree\fi{}K. Neptunium phosphide orders antiferromagnetically at 130 \ifmmode^\circ\else\textdegree\fi{}K with an incommensurate magnetic structure. At 74 \ifmmode^\circ\else\textdegree\fi{}K the magnetic structure becomes commensurate with the lattice (repeat distance 3.0 unit cells) and at lower temperatures tends to form a 3+, 3- sequence. A complete solution for the magnetic structure at low temperature is obtained by combining the neutron and M\"ossbauer results. Neptunium arsenide becomes antiferromagnetic at ${T}_{N}=175$ \ifmmode^\circ\else\textdegree\fi{}K. At \ensuremath{\sim} 160 \ifmmode^\circ\else\textdegree\fi{}K, the high-temperature 4+, 4- structure transforms to the type-I arrangement (simple +,- sequence). The crystal lattice of NpAs becomes tetragonal at ${T}_{N}$, exhibits a first-order transition to cubic symmetry at 142 \ifmmode^\circ\else\textdegree\fi{}K, and remains cubic at lower temperatures. The electrical resistivity increases by an order of magnitude on cooling from 142 to 141 \ifmmode^\circ\else\textdegree\fi{}K. Neptunium antimonide is a type-I antiferromagnet with ${T}_{N}=207$ \ifmmode^\circ\else\textdegree\fi{}K. The variation of the ordered moments ($\frac{1.4{\ensuremath{\mu}}_{B}}{\mathrm{Np}}$ in NpN to $\frac{2.5{\ensuremath{\mu}}_{B}}{\mathrm{Np}}$ in NpSb), paramagnetic effective moment ($\ensuremath{\sim}\frac{2.5{\ensuremath{\mu}}_{B}}{\mathrm{Np}}$), and the M\"ossbauer parameters (hyperfine field, quadrupole interaction, and isomer shift) all suggest a trend toward ${\mathrm{Np}}^{3+}$, $5{f}^{4}$ free-ion behavior in progressing from the nitride to the antimonide.

Magnetic properties of the neptunium monopnictides

The magnetic properties of the $R{\mathrm{Rh}}_{4}{\mathrm{B}}_{4}$ ($R$ represents rare-earth metal) compounds are discussed in terms of a combined crystalline-electric-field and molecular-field approach. Magnetization data taken on single-crystal Er${\mathrm{Rh}}_{4}$${\mathrm{B}}_{4}$ in five orientations are used to obtain the crystal-field and molecular-field coefficients, resulting in a complete analysis for the paramagnetic properties of this compound. The crystal-field parameters are additionally used to discuss all previously published magnetic data for polycrystalline $R{\mathrm{Rh}}_{4}{\mathrm{B}}_{4}$ compounds. For these highly anisotropic materials, the effect of preferential crystallite orientation on the observed data is pointed out. Consideration of the variation of the magnetic transition temperature ${T}_{m}$ between different constituent rare earths has verified a previous conclusion that the crystal field has a pronounced effect on ${T}_{m}$, but this alone does not fully explain the observations.

Crystal-field effects and the magnetic properties of rare-earth rhodium borides

The magnetic properties of a series of neptunium cubic C-15-type Laves phases ($\mathrm{Np}{X}_{2}$, where $X=\mathrm{Al}, \mathrm{Os}, \mathrm{Ir}, or \mathrm{Ru}$) have been studied between 1.5 and 300 \ifmmode^\circ\else\textdegree\fi{}K by means of magnetization and nuclear $\ensuremath{\gamma}$-ray resonance measurements. The properties show a systematic variation with neptunium-neptunium distance ${d}_{\mathrm{Np}}$. Thus, Np${\mathrm{Al}}_{2}$ (${d}_{\mathrm{Np}}=3.37$ A\AA{}) is ferromagnetic with a transition temperature ${T}_{c}=56$ \ifmmode^\circ\else\textdegree\fi{}K and an ordered moment of 1.5 ${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$/mole; Np${\mathrm{Os}}_{2}$ (${d}_{\mathrm{Np}}=3.26$ A\AA{}) is ferromagnetic with ${T}_{c}=7.5$ \ifmmode^\circ\else\textdegree\fi{}K and an ordered moment of 0.4 ${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$/mole; Np${\mathrm{Ir}}_{2}$ (${d}_{\mathrm{Np}}=3.25$ A\AA{}) is antiferromagnetic with ${T}_{c}=7.5$ \ifmmode^\circ\else\textdegree\fi{}K and an ordered moment of 0.6 ${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$/mole; and Np${\mathrm{Ru}}_{2}$ (${d}_{\mathrm{Np}}=3.23$ A\AA{}) does not order magnetically down to 1.5 \ifmmode^\circ\else\textdegree\fi{}K. This trend is interpreted in terms of an increase in the delocatlization of the neptunium magnetic moment and the magnetic $5f$ electrons, as ${d}_{\mathrm{Np}}$ decreases.

B. D. Dunlap

Papers

Electronic and magnetic properties of rare-earth ions in REBa2Cu3O7−x (RE=Dy, Ho, Er)

Coexistence of ordered magnetism and superconductivity in Pd 2 YbSn

Magnetic properties of the neptunium monopnictides

Crystal-field effects and the magnetic properties of rare-earth rhodium borides

Magnetic properties of neptunium Laves phases: Np Al 2 , Np Os 2 , Np Ir 2 , and Np Ru 2