Magnetocaloric effect in the intermetallic compound DyNi

Magnetic and heat capacity measurements have been carried out on the polycrystalline sample of DyNi which crystallizes in the orthorhombic FeB structure (space group Pnma). This compound is ferromagnetic with a Curie temperature of 59 K. Magnetization-field isotherms at low temperatures shows a step-like behavior characteristic of metamagnetic transitions. The magnetocaloric effect has been measured both in terms of isothermal magnetic entropy change and adiabatic temperature change for various applied magnetic fields. The maximum values of the entropy change and the temperature change are found to be 19 Jkg-1K-1 and 4.5 K, respectively, for a field of 60 kOe. The large magnetocaloric effect is attributed to the field-induced spin-flop metamagnetism occurring in this compound, which has a noncollinear magnetic structure at low fields.Comment: 11 page

Role of Fe substitution on the anomalous magnetocaloric and magnetoresistance behavior in Tb(Ni1-xFex)2 compounds

We report the magnetic, magnetocaloric and magnetoresistance results obtained in Tb(Ni1-xFex)2 compounds with x=0, 0.025 and 0.05. Fe substitution leads to an increase in the ordering temperature from 36 K for x=0 to 124 K for x=0.05. Contrary to a single sharp MCE peak seen in TbNi2, the MCE peaks of the Fe substituted compounds are quite broad. We attribute the anomalous MCE behavior to the randomization of the Tb moments brought about by the Fe substitution. Magnetic and magnetoresistance results seem to corroborate this proposition. The present study also shows that the anomalous magnetocaloric and magnetoresistance behavior seen in the present compounds is similar to that of Ho(Ni,Fe)2 compounds

Quantum Valence Criticality as Origin of Unconventional Critical Phenomena

It is shown that unconventional critical phenomena commonly observed in paramagnetic metals YbRh2Si2, YbRh2(Si0.95Ge0.05)2, and beta-YbAlB4 is naturally explained by the quantum criticality of Yb-valence fluctuations. We construct the mode coupling theory taking account of local correlation effects of f electrons and find that unconventional criticality is caused by the locality of the valence fluctuation mode. We show that measured low-temperature anomalies such as divergence of uniform spin susceptibility \chi T^{-\zeta) with $\zeta~0.6$ giving rise to a huge enhancement of the Wilson ratio and the emergence of T-linear resistivity are explained in a unified way.Comment: 5 pages, 3 figures, to be published in Physical Review Letter

On the Bragg, Leibfried, and Modified Leibfried Numbers

The Bragg, Leibfried, and modified Leibfried numbers are defined in the context of a theory of dislocation-mediated melting, and their values are determined from the properties of the dislocation ensemble at the melting temperature. The approximate numerical coincidence of the Bragg and modified Leibfried numbers is explained. The parameter K in the definition of the modified Leibfried number is shown to be the natural logarithm of the effective coordination number. Our analysis reveals that the Bragg number can be considered an elemental constant, in contrast to the Leibfried and modified Leibfried numbers.Comment: 5 pages, LaTe

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

Magnetocaloric effect in nano- and polycrystalline manganite La0.7Ca0.3MnO3La_{0.7}Ca_{0.3}MnO_3

$La_{0.7}Ca_{0.3}MnO_3$ samples were prepared in nano- and polycrystalline forms by sol-gel and solid state reaction methods, respectively, and structurally characterized by synchrotron X-ray diffraction. The magnetic properties determined by ac susceptibility and dc magnetization measurements are discussed. The magnetocaloric effect in this nanocrystalline manganite is spread over a broader temperature interval than in the polycrystalline case. The relative cooling power of the poly- and nanocrystalline manganites is used to evaluate a possible application for magnetic cooling below room temperature.Comment: 6 pages, 5 (double) figures, 1 table, 16 references; submitted to Appl. Phys.

Magnetism of (Dy0.5Er0.5)Al2 single crystal in ac and dc magnetic fields

The temperature (4.2–90 K), ac magnetic field (1.25–50 Oe), frequency (5–125 Hz), and bias dc magnetic field (0–10 kOe) dependencies of the real and imaginary components of the ac magnetic susceptibility, and the temperature (4.2–250 K) and dc magnetic field(0.1–50 kOe) dependencies of the dc magnetic susceptibility and magnetization of a(Dy0.5Er0.5)Al2 single crystal have been studied. Isothermal magnetization measurement in a dc magnetic field indicates that (Dy0.5Er0.5)Al2 orders ferromagnetically at 37 K. The ac and dc magnetic susceptibilities of (Dy0.5Er0.5)Al2 exhibit a similar behavior in the paramagnetic region but quite different behaviors in the ferromagnetic state. Both the real and imaginary components of the ac magnetic susceptibility are sensitive to the applied ac magnetic field, the crystallographic direction, and the bias magnetic field, showing that domain wall dynamics mainly account for the response to the ac magnetic field. The contributions to the magnetization process arise from the magnetically ordered Dy and Er sublattices and depend upon the single-ion anisotropy of the Dy and Er ions

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