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

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

Influence of Ge addition on the magnetocaloric effect of a Co-containing Nanopermtype alloy.

The influence of the partial substitution of B by Ge on the magnetocaloric response of Fe78Co5Zr6B10Cu1 is studied. Ge addition produces a reduction in the temperature at which the peak entropy change takes place, as well as a slight decrease in the magnitude of the peak, SM pk . The refrigerant capacity, RC, and its field dependence is also analyzed: although Ge addition increases RC of the Co-containing alloy, the largest RC value corresponds to the Co- and Ge-free alloy. This will be discussed on the basis of the recently proposed universal curve for the magnetic entropy change, which is also followed by the FeZrBCu Co,Ge alloy series

Roles of Critical Valence Fluctuations in Ce- and Yb-Based Heavy Fermion Metals

The roles of critical valence fluctuations of Ce and Yb are discussed as a key origin of several anomalies observed in Ce- and Yb-based heavy fermion systems. Recent development of the theory has revealed that a magnetic field is an efficient control parameter to induce the critical end point of the first-order valence transition. Metamagnetism and non-Fermi liquid behavior caused by this mechanism are discussed by comparing favorably with CeIrIn5, YbAgCu4, and YbIr2Zn20. The interplay of the magnetic order and valence fluctuations offers a key concept for understanding Ce- and Yb-based systems. It is shown that suppression of the magnetic order by enhanced valence fluctuations gives rise to the coincidence of the magnetic-transition point and valence-crossover point at absolute zero as a function of pressure or magnetic field. The interplay is shown to resolve the outstanding puzzle in CeRhIn5 in a unified way. The broader applicability of this newly clarified mechanism is discussed by surveying promising materials such as YbAuCu4, beta-YbAlB4, and YbRh2Si2.Comment: 17 pages, 8 figures, invited paper in special issue on strongly correlated electron system

Combined local-density and dynamical mean field theory calculations for the compressed lanthanides Ce, Pr, and Nd

This paper reports calculations for compressed Ce (4f^1), Pr (4f^2), and Nd (4f^3) using a combination of the local-density approximation (LDA) and dynamical mean field theory (DMFT), or LDA+DMFT. The 4f moment, spectra, and the total energy among other properties are examined as functions of volume and atomic number for an assumed face-centered cubic (fcc) structure.Comment: 15 pages, 9 figure

Magnetic, magneto-thermal and magneto-transport properties in SmMn2Si2-xGex compounds

The effect of Ge substitution for Si in SmMMn2Si2-xGex compounds has been studied. The Sm ordering temperature is found to be much larger in the compound with x=2, as compared to the compounds with x=0 and 1. The increase in the intra layer Mn-Mn distance is found to be responsible for this increase. Among these three compounds, SmMn2Ge2 is found to show re-entrant ferromagnetism at low temperatures. The magnetic contribution to the heat capacity has been found in all the three compounds. The splitting of the ground state multiplet has been estimated by fitting the magnetic part of the heat capacity data using the Schottky formula. The isothermal magnetic entropy change is found to remain the same for x=0 and 1, but decrease in the compound with x=2, though the nature of magnetic transition changes from second order to first order, as x is increased from 0 to 2. The electrical resistivity increases with Ge concentration. The excess resistivity in the antiferromagnetic region has been calculated

Complex magnetism of lanthanide intermetallics unravelled

We explain a profound complexity of magnetic interactions of some technologically relevant gadolinium intermetallics using an ab-initio electronic structure theory which includes disordered local moments and strong $f$-electron correlations. The theory correctly finds GdZn and GdCd to be simple ferromagnets and predicts a remarkably large increase of Curie temperature with pressure of +1.5 K kbar$^{-1}$ for GdCd confirmed by our experimental measurements of +1.6 K kbar$^{-1}$. Moreover we find the origin of a ferromagnetic-antiferromagnetic competition in GdMg manifested by non-collinear, canted magnetic order at low temperatures. Replacing 35\% of the Mg atoms with Zn removes this transition in excellent agreement with longstanding experimental data.Comment: 11 pages, 4 figure

Field dependence of the magnetocaloric effect in Gd and (Er 1-xDyx)Al2: Does a universal curve exist?

The field dependence of the magnetic entropy change of ferromagnetic lanthanide- based materials has been studied. The recently proposed master curve for the field dependence of the magnetocaloric effect of Fe-based amorphous alloys can also be constructed for these lanthanide-based crystalline materials, suggesting a universal behavior. The exponent n controlling the field dependence of the magnetic entropy change can be used for the interpretation of results in the case of multiple magnetic ordering phenomena