Magnetic order in TbNiAl and TbCuAl intermetallic compounds

Polycrystalline samples of the ternary intermetallics TbNiAl and TbCuAl are investigated by means of magnetization and neutron diffraction measurements. When Cu replaces Ni in the crystal structure, the magnetic behaviour is shown to be totally different, although both elements are non-magnetic. Analysis of the neutron spectra by the Rietveld refinement method gives evidence that TbNiAl orders antiferromagnetically whereas TbCuAl becomes ferromagnetic. Frustrated spins at the Tb atoms are found only in the TbNiAl compound. Their alignment changes at a second magnetic transition. The magnetic structures and the transition temperatures are discussed.     

Magnetic and magnetocaloric properties of the intermetallic compound TbNiAl

Magnetization measurements have been carried out on the intermetallic compound TbNiAl in applied fields up to 120 kOe. Temperature dependence of magnetization under zero-field-cooled and field-cooled conditions shows thermomagnetic irreversibility, which is attributed to magnetic frustration. With the increase of field, the irreversibility decreases and vanishes completely at high fields. Magnetocaloric effect has been calculated in terms of isothermal magnetic entropy change using magnetization isotherms obtained at various temperatures. The maximum entropy change is 13.8 J kg⁻¹ K⁻¹ near the ordering temperature for a field change of 50 kOe. The refrigerant capacity is found to be 494 J kg⁻¹ for the same field change and for a temperature difference of 52 K between the cold and the hot sinks.     

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.     

Magnetic properties of some Cr-Ga intermetallic compounds

Magnetic susceptibility measurements in the range 10 – 300 K on the compounds Cr₃Ga, CrGa, Cr₅Ga₆ and CrGa₄ are reported here. All except CrGa₄ appeared to be Pauli paramagnetic, but CrGa₄ appeared to be basically diamagnetic with a parasitic weak ferromagnetic component.     

Magnetic properties of some gadolinium—Cobalt intermetallic compounds

Crystallographic and magnetic properties of the single crystals having the compositions of GdCo₃, Gd₂Co₇, GdCo₅, Gd_2.2Co_16.6 and Gd₂Co₁₇ were studied in order to contribute to the investigation of the magnetic anisotropy in the Gd–Co system. The single crystal used were prepared by means of the Bridgman method using BN-coated alumina crucibles.The room-temperature magnetocrystalline anisotropy constants K₁ of GdCo₃, Gd₂Co₇, GdCo₅, Gd_2.2Co_16.6 and Gd₂Co₁₇ are determined as 8.1 × 10⁶, 1.3 × 10⁷, 4.1 × 10⁷, 3.0 × 10⁶ and -2.7 × 10⁶ erg/cm³, respectively. it is also found that the magnetocrystalline anisotropy of Gd–Co phases in the stable region of the Th₂Zn₁₇-type structure changes very sensitively from negative to positive as the ratio Gd/Co increases above the stoichiometric ratio of 2/17.     

Magnetic properties of intermetallic ruthenium compounds with the CsCl structure

Magnetization measurements on six ruthenium compounds with the CsCl structure (B2-compounds) are reported. The magnetic properties can be described in terms of a temperature independent Pauli susceptibility and a contribution of localized moments of about 4μ_B which are very likely connected with magnetic centers consisting of one ruthenium atom which substitutes for an X-atom in an otherwise ordered compound RuX and its eight nearest neighbours. The results show that a weak antiferromagnetic coupling exists between these moments of which the concentration is about 0.003 per ruthenium atom.     

Magnetic field controlled floating-zone single crystal growth of intermetallic compounds

Radio-frequency (RF) floating zone single crystal growth is an important technique for the preparation of single bulk crystals. The advantage of the floating-zone method is the crucible-free growth of single crystals of reactive materials with high melting points. The strong heat diffusion on the surface, as well as the melt convection in the molten zone due to induction heating, often leads to an undesired solid-liquid interface geometry with a concave (towards the solid phase) outer rim. These concave parts aggravate the single crystal growth over the full cross-section. A two-phase stirrer was developed at IFW Dresden in order to avoid the problems connected with these concave parts. It acts as a magnetic field pump and changes the typical double vortex structure to a single roll structure, thus pushing hot melt into the regions where the concave parts may arise. The current in the secondary coil is induced by the primary coil, and the capacitor and the resistance of the secondary circuit are adjusted to get a stable 90 degree phase-shift between the coil currents. Single crystal growth of industrial relevant RuAl and TiAl intermetallic compounds was performed based on the material parameters and using the adjusted two-phase stirrer. Very recently, the magnetic system was applied to the crystal growth of biocompatible TiNb alloys and antiferromagnetic Heusler MnSi compounds.     

Magnetic susceptibility of intermetallic compounds in the Er-In system at high temperatures

The temperature dependence of the magnetic susceptibility (T) of intermetallic compounds of Er with In in a wide temperature range from 20 to 1600°C inherent in the solid state and melting process of the materials under review was studied for the first time by the Faraday method. For all test compounds, the temperature dependence was found to be approximated by the Curie-Weiss linear law both in a solid and liquid state. The Curie paramagnetic temperature, Curie-Weiss constants, and effective magnetic moment numbers per Er atom were calculated by computer processing of the ^–1(T) data, using the least-squares technique. A semiempirical estimation of the indirect exchange interaction parameter showed the test compounds to be characterized by exchange interactions of the Ruderman-Kittel-Kasuya-Yosida type.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 7–10, December 2004     

Magnetic properties and magnetocaloric effects in Er_(1-x)Gd_xCoAl intermetallic compounds

The magnetism and magnetocaloric effect in Er1-xGdxCoAl(x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1) were investigated. The Er1-xGdxCoAl compounds were synthesized by arc melting. With the increasing Gd content, the N′eel temperature(T N)linearly increases from 14 K to 102 K, while the magnetic entropy change(-?S M) tends to decrease nonmonotonously.Under the field change from 0 T to 5 T, the-?S M of the compounds with x = 0.2–1 are stable around 10 J/kg·K, then a cooling platform between 20 K and 100 K can be formed by combining these compounds. For x = 0.6, 0.8, 1.0, the compounds undergo two successive magnetic transitions, one antiferromagnetism to ferromagnetism and the other ferromagnetism to paramagnetism, with increasing temperature. The two continuous magnetic transitions in this series are advantageous to broaden the temperature span of half-peak width(δT) in the-?S M–T curve and improve the refrigeration capacity.     

Magnetic aftereffect associated with narrow domain walls in some rare earth based intermetallic compounds

Using quasi-static fields and pulsed fields we have measured the magnetization rate dM/dt = v as a function of field H for Dy₃Al₂ and DyCoNi which present narrow domain walls. The experimental results follow the empirical law v = v∞ exp (−H_o/H). An analogous experimental law has been observed for domain reversal in ferroelectrics and for dislocation motion.     

Hydrides of intermetallic compounds

Aspects of the progress over the recent years on hydrides of intermetallic compounds are reviewed with emphasis on structure, stability, solid-state properties, catalysis, and kinetics. Some new routes to an understanding of hydride phenomenology are indicated. Generally speaking hydrides represent but one special aspect of intermetallic compounds. They are, however, unique as model systems for questions concerning the stability of intermetallics in general, as thermodynamic data become more readily available during synthesis than is the case with most other metallic systems. Stability criteria are exemplified on model systems chosen to represen instructive or extreme cases. Hydrides are, moreover, unique with respect to the unusual properties of hydrogen as a “metallic” component, especially concerning such characteristics as mass (light), size (ranging from average to exceedingly small as a proton) and electronegativity (relatively high and comparable to B). This promises a wealth of special solid-state properties concerning magnetism, electrical conductivity or superconductivity. Some selected examples in this direction are discussed with emphasis on questions pertaining to the electronic state and the stability of the hydrides. The kinetics of compound (hydride) formation are often extraordinarily fast around ambient conditions opening this facet of intermetallics to rigorous study. Also intriguing new catalytic activity has been identified with metal hydrides implicating in one way or another the special surface properties of metal hydrides. Finally, metal hydrides are gaining in importance with respect to technological applications within a projected hydrogen economy (H or heat storage, electrochemical cells, etc.). Many of the fundamental aspects of metal hybrides have therefore become of practical relevance. Financial support by the Department of Energy, Division of Basic Energy Sciences, is acknowledged.     

Magnetism and superconductivity in intermetallic uranium compounds

Superconductivity, spin-fluctuation effects and magnetic order are reviewed for intermetallic compounds of uranium with d-transition elements. Large values for the effective mass of the pairing electrons are deduced from critical field studies on the superconducting compounds. Magnetism in the 5f-electron compounds is strongly anisotropic even for paramagnetic materials. Magnetic order does not frequently occur in these intermetallics, spin fluctuations are often observed. A unique combination of spin-fluctuation phenomena and superconductivity is met in UPt₃.     

Magnetic symmetry in rare intermetallic compounds with CaZn5 type of structure

New magnetic structures which can arise in rare earth intermetallic compounds with CaZn₅ type of structure are suggested using a well known group theoretical method derived from the Landau theory of the second order phase transitions. Only symmetry consideratations are taken into account.