Lanthanide Al-Ni base Ericsson cycle magnetic refrigerants

A magnetic refrigerant for a magnetic refrigerator using the Ericsson thermodynamic cycle comprises DyAlNi and (Gd.sub.0.54 Er.sub.0.46)AlNi alloys having a relatively constant ΔTmc over a wide temperature range

Erbium-based magnetic refrigerant (regenerator) for passive cryocooler

A two stage Gifford-McMahon cryocooler having a low temperature stage for reaching approximately 10K, wherein the low temperature stage includes a passive magnetic heat regenerator selected from the group consisting of Er.sub.6 Ni.sub.2 Sn, Er.sub.6 Ni.sub.2 Pb, Er.sub.6 Ni.sub.2 (Sn.sub.0.75 Ga.sub.0.25), and Er.sub.9 Ni.sub.3 Sn comprising a mixture of Er.sub.3 Ni and Er.sub.6 Ni.sub.2 Sn in the microstructure

Electrical resistivity, electronic heat capacity, and electronic structure of Gd5Ge4

Temperature and dc magnetic-field dependencies of the electrical resistivity (4.3–300 K, 0–40 kOe) and heat capacity (3.5–14 K, 0–100 kOe) of polycrystalline Gd5Ge4 have been measured. The electrical resistivity of Gd5Ge4 shows a transition between the low-temperature metallic and high-temperature insulatorlike states at ∼130 K. In the low-temperature metallic state both the resistivity and electronic heat capacity of Gd5Ge4 indicate a possible presence of a narrow conduction band. Both low- and high-temperature behaviors of the electrical resistivity of Gd5Ge4 correlate with the crystallographic and magnetic phase transitions induced by temperature and/or magnetic field. Several models, which can describe the unusual behavior of the electrical resistance of Gd5Ge4 above 130 K, are discussed. Preliminary tight-binding linear muffin-tin orbital calculations show that Gd5Ge4 behaves as a metal in the low-temperature magnetically ordered state, and as a Mott-Hubbard “semiconductor” in the high-temperature magnetically disordered state

Permanent magnet structure for generation of magnetic fields

A permanent magnet structure for maximizing the flux density per weight of magnetic material comprising a hollow body flux source for generating a magnetic field in the central gap of the hollow body, the magnetic field having a flux density greater than the residual flux density of the hollow body flux source. The hollow body flux source has a generally elliptic-shape, defined by unequal major and minor axis. These elliptic-shaped permanent magnet structures exhibit a higher flux density at the center gap while minimizing the amount of magnetic material used. Inserts of soft magnetic material proximate the central gap, and a shell of soft magnetic material surrounding the hollow body can further increase the strength of the magnetic field in the central gap by reducing the magnetic flux leakage and focusing the flux density lines in the central gap

The crystal structure and magnetic properties of Pr117Co56.7Ge112

The ternary intermetallic compound Pr117Co56.7 Ge 112 adopts the cubic Tb117Fe52 Ge 112-type related structure with the lattice parameter a = 29.330(3) Å. The compound exhibits one prominent magnetic transition at ∼10 K and two additional weak magnetic anomalies are observed at ∼26 K and ∼46 K in a 1 kOe applied field. At a higher field of 10 kOe, only one broad ferromagnetic-like transition remains at 12 K. The inverse magnetic susceptibility of Pr117Co56.7 Ge 112 obeys the Curie-Weiss law with a positive value of the paramagnetic Curie temperature (θP = 24 K), indicating that ferromagnetic interactions are dominant. The effective magnetic moment is 3.49 μ B/Pr, which is close to the theoretical effective paramagnetic moment of 3.58 μ B for the Pr3+ ion

Decoupling of the Magnetic and Structural Transformations in Er5Si4

Er5Si4 is a member of the R5(Si4−xGex) family of alloys, where R=rare earth metal. Many of these compounds display a strong coupling between the magnetic and crystal lattices. In the naturally layered R5(Si4−xGex) materials, inter- and intralayer interactions can be controlled by chemical and physical means; thus their physical properties can be tailored within wide limits. The Er5Si4 is unique in that the temperature dependent structural sequence is opposite that of other representatives of this family. The magnetism of Er5Si4 is reflective of its exceptional place within the series

Making and Breaking Covalent Bonds across the Magnetic Transition in the Giant Magnetocaloric Material Gd5(Si2Ge2)

A temperature-dependent, single crystal x-ray diffraction study of the giant magnetocaloric material, Gd5(Si2Ge2), across its Curie temperature (276 K) reveals that the simultaneous orthorhombic to monoclinic transition occurs by a shear mechanism in which the (Si,Ge)−(Si,Ge) dimers that are richer in Ge increase their distances by 0.859(3) Å and lead to twinning. The structural transition changes the electronic structure, and provides an atomic-level model for the change in magnetic behavior with temperature in the Gd5(SixGe1−x)4

Phase relationships and structural, magnetic, and thermodynamic properties of alloys in the pseudobinary Er5Si4-Er5Ge4 system

The room temperature crystal structures of Er5SixGe4−x alloys change systematically with the concentration of Ge from the orthorhombic Gd5Si4-type when x=4, to the monoclinic Gd5Si2Ge2 type when 3.5⩽x⩽3.9 and to the orthorhombic Sm5Ge4 type forx⩽3. The Curie-Weiss behavior of Er5SixGe4−x materials is consistent with the Er3+ state. The compounds order magnetically below 30 K, apparently adopting complex noncollinear magnetic structures with magnetization not reaching saturation in 50 kOe magnetic fields. In Er5Si4, the structural-only transformation from the monoclinic Gd5Si2Ge2-type to the orthorhombic Gd5Si4-type phase occurs around 218 K on heating. Intriguingly, the temperature of this polymorphic transformation is weakly dependent on magnetic fields as low as 40 kOe (dT∕dH=−0.058 K∕kOe) when the material is in the paramagnetic state nearly 200 K above its spontaneous magnetic ordering temperature. It appears that a magnetostructural transition may be induced in the 5:4 erbium silicide at ∼18 K and above by 75 kOe and higher magnetic fields. Only Er5Si4 but none of the other studied Er5SixGe4−x alloys exhibit magnetic field induced transformations, which are quite common in the closely related Gd5SixGe4−x system. The magnetocaloric effects of the Er5SixGe4−x alloys are moderate

Magnetic anisotropy and magnetic phase diagram of Gd5Ge4

The magnetization of single crystal Gd5Ge4, which in a zero magnetic field orders antiferromagnetically at 128 K, indicates a reversible spin-flop transition when the magnetic field is along the c axis and the absence of similar transformations when the magnetic field vector is perpendicular to the c axis. This anisotropic behavior is due to variation of magnetization energy between the c axis and the a or b axes of the orthorhombic crystal caused by a different alignment of the Gd moments with respect to the magnetic field vector. The anisotropy of the antiferromagnetic state diminishes with the increasing magnetic field and temperature. The critical magnetic field for the antiferromagnetic-ferromagnetic transition is the smallest and the ferromagnetic state is most stable when the magnetic field vector is parallel to the b axis, indicating an easy magnetization direction along this axis. The anisotropy of the magnetic field-induced transformation in Gd5Ge4 is discussed in connection with the coupled magnetic and structural transitions. Anisotropic magnetic phase diagrams along the three major crystallographic axes are constructed