Hexagonal Intermetallic Compounds Research Articles

Anisotropy in the paramagnetic phase of RENi 5 hexagonal intermetallic compounds (RE = Tb, Ho, Nd)

A new alternative experimental method, the measurement of the polar dependence of the parallel and perpendicular magnetization components, is reported in order to determine all the individual components of the magnetic susceptibility tensors of second and fourth rank. Suitable theoretical expressions have been obtained for hexagonal systems with 6/mmm, 622, 6mm, and 6 m2 point symmetries. An extensive experimental study, following the method proposed, has been performed in the paramagnetic phase of RENi 5(RE = Tb, Ho, Nd) hexagonal intermetallic compounds. The interpretation of these results in terms of a microscopic model involving crystalline-electric-field, bilinear exchange, and total quadrupolar interactions is also reported.

Magnetic ordering and frustration in hexagonal UNi4B.

We have determined unusual magnetic ordering of the hexagonal intermetallic uranium compound U${\mathrm{N}}_{\mathrm{i}4}$B via neutron diffraction. In the easy basal plane the U moments have triangular symmetry with antiferromagnetic interactions. Along the hard $c$ axis ferromagnetic coupling occurs. Below ${T}_{N}=20$ K only two out of every three U moments of $1.2{\ensuremath{\mu}}_{B}$ order in vortexlike arrangements around the third paramagnetic spin. This novel magnetic structure is related to the occurrence of a crystallographic superstructure. Previously observed anomalies in bulk properties below ${T}_{N}$ are attributed to unconventional spin-wave excitations associated with this type of ordering.

μSR study of RNi5 intermetallics where R=La, Gd or Tb

Zero-field μSR studies of some hexagonal intermetallic compounds are described. Our LaNI5 data provide information on the muon localisation site. This site could be one of the deuterium sites deduced from neutron diffraction. A comparison of the temperature dependence of the exponential damping rate, λ(T), of our samples shows that λ(T) is strongly influenced by crystal field effects. The TbNi5 spectra exhibit two components forT<60 K. We discuss the possible explanations of this result. We see a μSR signal below the magnetic phase transition in GdNi5. This makes the study of the spin-lattice relaxation rate possible in the ordered magnetic state.

Anomalous behavior in the low temperature properties of UPd 3

The low temperature specific heat of the hexagonal intermetallic compound UPd 3 reveals a contribution from low lying crystal field levels. In annealed or single crystal samples, sharp phase transitions are observed at temperatures of 6 and 7 K respectively. Correlation with resistivity, susceptibility and X-ray measurements in this temperature range indicate that the collective phenomenon is probably due to the electric quadrupole interaction between the U 4+ ions.

Evidence of disordered substitutions in the “Th 2Ni 17-type” structure. Exact structure determination of the ThNi, YNi and ErCo compounds

Hexagonal intermetallic compounds close to R 2M 17 stoichiometry in the ThNi, YNi and ErCo systems have been studied by single crystal X-ray techniques. All of these compounds have been previously reported as belonging to the Th 2Ni 17-type structure. In fact, this structure type does not exist but is an ideal case. The nature of the observed extinctions and refinement of the crystal structures show that substitutions must occur on all R rows parallel to the c -axis with the subsequent displacements of the M atoms. This leads to a non-stoichiometric composition, e.g., ThNi 9.5.

Neutron diffraction study of MnB 2

It is found that the hexagonal intermetallic compound MnB 2 is antiferromagnetic. The magnetic moments are ferromagnetically coupled in the base plane and are perpendicular to the c-axis. The magnitude of the magnetic moments per manganese atom is 2.6μ B .

Physical metallurgy and magnetic measurements of SmCo&amp;lt;inf&amp;gt;5&amp;lt;/inf&amp;gt;-SmCu&amp;lt;inf&amp;gt;5&amp;lt;/inf&amp;gt;alloys

The magnetic properties of the hexagonal intermetallic compounds involving the rare-earth and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3d</tex> transition metals have been reported in the literature. These alloys look promising as fine-particle permanent magnets. A large number of samples in the system SmCo <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5-x</inf> Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> were prepared by induction melting under a protective atmosphere, and annealed at various temperatures. An outstanding feature of these alloys is their high intrinsic coercive force. After annealing at low temperatures, they show coercive forces above 20 kOe and an energy product of about 8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> G.Oe. The most important factors determining the coercive force appear to be the chemical composition, the cooling rate, the alignment of the SmCO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> -rich phase, and the annealing treatment. Examination by electron microscopy and electron probe techniques suggests a spinodal decomposition of a supersaturated solid solution into two phases, one rich in SmCo <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> and the other rich in SmCu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> .

New Permanent Magnet Materials Containing Rare-Earth Metals

Previously, most basic magnetic properties of the hexagonal intermetallic compounds involving the rare-earth (RE) and 3-d transition elements were reported in the literature. In addition, some of these compounds were investigated by various workers for permanent magnet properties by grinding ingots of the compounds into very fine powder. Recently, we discovered new permanent magnet materials which were based mostly on the hexagonal intermetallic compounds Co5RE. Replacement of cobalt with copper in some of these rare-earth compounds resulted in solid materials having substantial permanent magnet properties. An outstanding feature of these alloys is their high value of intrinsic coercive force. High-energy product alloys were found in the Co5−xCuxSm and Co5−xCoxCe systems with iron additions. Small pieces of Co3.5Fe0.4Cu1.35Sm exhibited BR=6450 G, BHC=4000 Oe, and (BH)m=9×105 G Oe. Also, small pieces of Co3.5Fe0.5CuCe exhibited BR=5100 G, BHC=3500 Oe, and (BH)m=5.2×106 G Oe. In general, these alloys are prepared by inert-electrode arc melting, resulting in a relatively rapid freezing from the molten state. The samples are then given a low-temperature anneal. Cross sections of the specimens show microstructural directionality which is a result of freezing in a direction normal to the cold surface of the hearth. These directional effects appear to be associated with the directional magnetic properties that are important because of the high crystal anisotropy of the alloys. When a specimen of the composition Co3.45Fe0.25Cu1.35Sm was annealed at 1100°C and examined by optical-microscope and electron-probe techniques, particles rich in Co5Sm were observed to be embedded in a Cu5Sm-rich matrix. The iron appeared largely in the cobalt-rich phase. The cobalt-rich particles were approximately 2.5×10 μ. Further work is in progress to improve directional properties and thus further improve the magnetic properties.

NEW PERMANENT MAGNET MATERIALS

New permanent magnet materials containing rare-earth elements (RE) have been discovered. For the most part, these alloys are based on the hexagonal intermetallic compounds, Co5RE. Replacement of cobalt with copper in some of these rare-earth compounds results in solid materials with substantial permanent magnet properties. Coercive forces as high as 28,700 Oe have been obtained in heat-treated samples of alloys in the Co5Sm–Cu5Sm system.

Mössbauer-Effect Determination of Crystalline Electric Field Splittings in Several Intermetallic Compounds of Thulium

By measuring the temperature dependence of the nuclear quadrupole splitting of the ${\mathrm{Tm}}^{169}$ 8.4-keV M\"ossbauer $\ensuremath{\gamma}$ transition, a measure of the strength of the crystalline electric field (CEF) in several hexagonal intermetallic compounds of the type $\mathrm{Tm}{X}_{2}$, where $X$ is another transition element, has been obtained. As in thulium metal, a zero-order model of the CEF incorporating only the ${{C}_{2}}^{0}$ parameter is found sufficient to describe the experimental results. On this basis, the over-all CEF splitting of the $^{3}H_{6}$ ground term of the ${\mathrm{Tm}}^{3+}$ ion is found to be 94 ${\mathrm{cm}}^{\ensuremath{-}1}$ in Tm${\mathrm{Ru}}_{2}$, 88 ${\mathrm{cm}}^{\ensuremath{-}1}$ in Tm${\mathrm{Re}}_{2}$, and 42 ${\mathrm{cm}}^{\ensuremath{-}1}$ in Tm${\mathrm{Mn}}_{2}$. The nuclear and ionic shielding parameters ${R}_{Q}$ and ${\ensuremath{\sigma}}_{2}$ were also determined from the experimental measurements, in reasonable agreement with theoretical expectations. Best agreement between experimental and calculated values of the CEF parameters is obtained when the effective charge on the $X$ ions is taken to be zero. Details of the calculation of the CEF parameter ${{C}_{2}}^{0}$ by the plane-wise summation method for the hexagonal Laves-phase intermetallics are also given.

The elastic constants of the intermetallic compound Ag 2Al from 77° TO 700°K

The five independent elastic constants of the hexagonal intermetallic compound Ag 2Al were determined by means of the ultrasonic pulse-echo technique over the temperature interval 77° to 700°K. The values obtained at 298°K are: c 11 = 1·415 , c 33 = 1·685 , c 44 = 0·341 c 66 = 0·284 , and c 13 = 0.747 , all expressed in units of 10 12 dyn/cm 2. The linear compressibility parallel to the c-axis, calculated from these elastic constants is smaller than the compressibility perpendicular to the c-axis, in agreement with the less-than-ideal c a ratio. Extrapolating the elastic constants to 0°K, the Debye temperature was calculated to be 276°K.