Hydrostatic pressure-induced modifications of structural transitions lead to large enhancements of magnetocaloric effects in MnNiSi-based systems

A remarkable decrease of the structural transition temperature of MnNiSi from 1200 to transitions, leading to a large magnetocaloric effect near room temperature. Application of relatively low hydrostatic pressures (∼2.4 kbar) lead to an extraordinary enhancement of the isothermal entropy change from -ΔS=44 to 89 J/kgK at ambient and 2.4 kbar applied pressures, respectively, for a field change of ΔB=5T, and is associated with a large relative volume change of about 7% with P=2.4 kbar

Anomalous metamagnetism in the low carrier density Kondo lattice YbRh3Si7

We report complex metamagnetic transitions in single crystals of the new low carrier Kondo antiferromagnet YbRh3Si7. Electrical transport, magnetization, and specific heat measurements reveal antiferromagnetic order at T_N = 7.5 K. Neutron diffraction measurements show that the magnetic ground state of YbRh3Si7 is a collinear antiferromagnet where the moments are aligned in the ab plane. With such an ordered state, no metamagnetic transitions are expected when a magnetic field is applied along the c axis. It is therefore surprising that high field magnetization, torque, and resistivity measurements with H||c reveal two metamagnetic transitions at mu_0H_1 = 6.7 T and mu_0H_2 = 21 T. When the field is tilted away from the c axis, towards the ab plane, both metamagnetic transitions are shifted to higher fields. The first metamagnetic transition leads to an abrupt increase in the electrical resistivity, while the second transition is accompanied by a dramatic reduction in the electrical resistivity. Thus, the magnetic and electronic degrees of freedom in YbRh3Si7 are strongly coupled. We discuss the origin of the anomalous metamagnetism and conclude that it is related to competition between crystal electric field anisotropy and anisotropic exchange interactions.Comment: 23 pages and 4 figures in the main text. 7 pages and 5 figures in the supplementary materia

Intermediate valence to heavy fermion through a quantum phase transition in Yb3(Rh1−xTx)4Ge13 (T=Co,Ir) single crystals

Single crystals of Yb3(Rh1−xTx)4Ge13 (T=Co,Ir) have been grown using the self-flux method. Powder x-ray diffraction data on these compounds are consistent with the cubic structure with space group Pm3¯n. Intermediate-valence behavior is observed in Yb3(Rh1−xTx)4Ge13 upon T = Co doping, while T = Ir doping drives the system into a heavy-fermion state. Antiferromagnetic order is observed in the Ir-doped samples Yb3(Rh1−xTx)4Ge13 for 0.5<x≤1 with TN=0.96 K for Yb3Ir4Ge13. With decreasing x, the magnetic order is suppressed towards a quantum critical point around xc = 0.5, accompanied by non-Fermi-liquid behavior evidenced by logarithmic divergence of the specific heat and linear temperature dependence of the resistivity. The Fermi-liquid behavior is recovered with the application of large magnetic fields

Effects of hydrostatic pressure on magnetostructural transitions and magnetocaloric properties in (MnNiSi)1-x(FeCoGe)x

The isostructural alloying of two compounds with different magnetic and thermo-structural properties has resulted in a new system, (MnNiSi)1-x(FeCoGe)x, that exhibits large magnetocaloric effects with acute sensitivity to both compositional variation and applied hydrostatic pressure. The maximum isothermal entropy change reaches a value of -ΔSmax=143.7J/kg K for a field change of ΔB=5T at atmospheric pressure. The first-order magnetostructural transition responsible for the entropy change shifts to lower temperature with applied hydrostatic pressure (∼-10K/kbar) but maintains a large value of -ΔSmax