arXiv subjects

M. C. Aronson

Publications and source records attributed to M. C. Aronson.

47 records · Page 3Linked to original sources

arXiv2008

A New Unconventional Antiferromagnet, Yb$_3$Pt$_4$

We report the synthesis and basic properties of single crystals of a new binary compound, Yb$_{3}$Pt$_{4}$. The Yb ions in this compound are fully trivalent, and heat capacity measurements show that the crystal field scheme involves a doublet ground state, well separated from the excited states, which are fully occupied above $\sim$ 150 K. The heat capacity displays a large, weakly first order anomaly at 2.4 K, where a cusp is observed in the magnetic susceptibility signalling the onset of antiferromagnetic order. The entropy associated with this order is the full Rln2 of the doublet ground state, however the magnetic susceptibility in the ordered phase is dominated by a large and temperature independent component below the Neel temperature. The heat capacity in the ordered state originates with ferromagnetic spin waves, giving evidence for the inherently local moment character of the ordered state. The electrical resistivity is unusually large, and becomes quadratic in temperature exactly at the Neel temperature. The absence of analogous Fermi liquid behavior in the heat capacity and the magnetic susceptibility implies that Yb$_{3}$Pt$_{4}$ is a low electron density system, where the Fermi surface is further gapped by the onset of magnetic order.

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arXiv2008

Yb$_{2}$Pt$_{2}$Pb: Magnetic frustration in the Shastry-Sutherland lattice

We have synthesized single crystals of Yb$_{2}$Pt$_{2}$Pb, which crystallize in the layered U$_{2}$Pt$_{2}$Sn-type structure, where planes of Yb ions lie on a triangular network. We report here the first results of magnetization, specific heat, and electrical resistivity experiments. The lattice constants and high temperature magnetic susceptibility indicate that the Yb ions are trivalent, while Schottky peaks in the specific heat show that the ground state is a well isolated doublet. Significant magnetic anisotropy is observed, with the ratio of susceptibilities perpendicular and parallel to the magnetic planes differing by as much as a factor of 30 at the lowest temperatures. Antiferromagnetic order occurs at a Néel temperature $T_{\rm N}$=2.07 K, a transition temperature which is more than an order of magnitude smaller than the mean field interactions reflected by the in-plane Weiss temperature. Further evidence for short ranged magnetic fluctuations is found in the magnetic susceptibility and electrical resistivity, which have broad peaks above $T_{\rm N}$, and in the slow development of the magnetic entropy at $T_{\rm N}$. Our experiments indicate that Yb$_{2}$Pt$_{2}$Pb is a quasi-two dimensional and localized moment system, where strong magnetic frustration may arise from the geometry of the underlying Shastry-Sutherland lattice.

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arXiv2007

Crystalline electric fields and the magnetic ground state of the novel Heusler intermetallic YbRh$_{2}$Pb

We have synthesized a new intermetallic compound with a distorted Heusler structure, YbRh$_{2}$Pb. We present a study of the magnetic, thermal, and transport properties. Heat capacity measurements revealed that YbRh$_{2}$Pb orders magnetically below T$_{N}$=0.57 K from a paramagnetic state with substantial crystal electric field splitting. Magnetic field further splits the ground state, which leads to the suppression of magnetic order in YbRh$_{2}$Pb.

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arXiv2007

Elastic neutron scattering in Quantum Critical Antiferromagnet Cr$_{0.963}$V$_{0.037}$

We have performed elastic neutron scattering studies of the quantum critical antiferromagnet Cr$_{0.963}$V$_{0.037}$. We have found that unlike pure Cr, which orders at two incommensurate wavevectors, Cr$_{0.963}$V$_{0.037}$ orders at four incommensurate and one commensurate wavevectors. We have found strong temperature dependent scattering at the commensurate and incommensurate wavevectors below 250 K. Results indicate that the primary effect of V doping on Cr is the modification of the nesting conditions of the Fermi surface and not the decreasing of the Neel temperature.

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arXiv2006

Crystalline electric fields and the ground state of Ce$_{3}$Rh$_{4}$Pb$_{13}$

We have succeeded in synthesizing of single crystals of a new intermetallic compound, Ce$_{3}$Rh$_{4}$Pb$_{13}$. Magnetic susceptibility measurements indicate that the Ce moments are highly localized, despite the metallic character of the electrical resistivity. Heat capacity measurements reveal that the cubic crystal electric field lifts the six-fold degeneracy of the Ce$^{3+}$ ground state, with the quartet state separated by approximately 60 K from the doublet ground state. The magnetic field dependence of the heat capacity at low temperature indicates a further splitting of the doublet, but no sign of magnetic order was found above 0.35 K.

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arXiv2005

Critical Phenomena and the Quantum Critical Point of Ferromagnetic Zr1-xNbxZn2

We present a study of the magnetic properties of Zr1-xNbxZn2, using an Arrott plot analysis of the magnetization. The Curie temperature TC is suppressed to zero temperature for Nb concentration xC=0.083+/-0.002, while the spontaneous moment vanishes linearly with TC as predicted by the Stoner theory. The initial susceptibility chi displays critical behavior for x<=xC, with a critical exponent which smoothly crosses over from the mean field to the quantum critical value. For high temperatures and x<=xC and for low temperatures and x>=xC we find that chi^(-1)=chi_o^(-1)+aT^(4/3), where chi_o^(-1) vanishes as x approaches xC. The resulting magnetic phase diagram shows that the quantum critical behavior extends over the widest range of temperatures for x=xC, and demonstrates how a finite transition temperature ferromagnet is transformed into a paramagnet, via a quantum critical point.

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arXiv2005

Non-Fermi-liquid behavior in Ce(Ru$_{1-x}$Fe$_x$)$_2$Ge$_2$: cause and effect

We present inelastic neutron scattering measurements on the intermetallic compounds Ce(Ru$_{1-x}$Fe$_x$)$_2$Ge$_2$ ($x$=0.65, 0.76 and 0.87). These compounds represent samples in a magnetically ordered phase, at a quantum critical point and in the heavy-fermion phase, respectively. We show that at high temperatures the three compositions have the identical response of a local moment system. However, at low temperatures the spin fluctuations in the critical composition are given by non-Fermi-liquid dynamics, while the spin fluctuations in the heavy fermion system show a simple exponential decay in time. In both compositions, the lifetime of the fluctuations is determined solely by the distance to the quantum critical point. We discuss the implications of these observations regarding the possible origins of non-Fermi-liquid behavior in this system.

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arXiv2003

Magnetotransport in Single Crystal Half-Heusler Compounds

We present the results of electrical resistivity and Hall effect measurements on single crystals of HfNiSn, TiPtSn, and TiNiSn. Semiconducting behavior is observed in each case, involving the transport of a small number of highly compensated carriers. Magnetization measurements suggest that impurities and site disorder create both localized magnetic moments and extended paramagnetic states, with the susceptibility of the latter increasing strongly with reduced temperature. The magnetoresistance is sublinear or linear in fields ranging from 0.01 - 9 Tesla at the lowest temperatures. As the temperature increases, the normal quadratic magnetoresistance is regained, initially at low fields, and at the highest temperatures extending over the complete range of fields. The origin of the vanishingly small field scale implied by these measurements remains unknown, presenting a challenge to existing classical and quantum mechanical theories of magnetoresistance.

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arXiv2003

The Origin of Weak Ferromagnetism in CaB6

We have combined the results of magnetization and Hall effect measurements to conclude that the ferromagnetic moments of lightly doped CaB6 samples display no systematic variation with electron doping level. Removal of the surface with acid etching substantially reduces the measured moment, although the Hall constant and resistivity are unaffected, indicating that the ferromagnetism largely resides on and near the sample surface. Electron microprobe experiments reveal that Fe and Ni are found at the edges of facets and growth steps, and on other surface features introduced during growth. Our results indicate that the weak ferromagnetism previously reported in undoped CaB6 is at least partly extrinsic.

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arXiv2002

non-Local Quantum Criticality in Ce(Ru_{1-x} Fe_x)_2 Ge_2 (x = x_c = 0.76)

We present the results of inelastic neutron scattering measurements, performed near the antiferromagnetic quantum critical point in Ce(Ru_{0.24} Fe_{0.76})_2 Ge_2. Both local and long range fluctuations of the local moments are observed, but due to the Kondo effect only the latter are critical. We propose a phenomenological expression which fits the energy $E$, temperature T and wave vector q dependences of the generalized susceptibility chi(q,E,T), describing the non-Fermi liquid E/T scaling found at every wave vector.

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arXiv1999

Magnetotransport in the low carrier density ferromagnet EuB_6

We present a magnetotransport study of the low--carrier density ferromagnet EuB_6. This semimetallic compound, which undergoes two ferromagnetic transitions at T_l = 15.3 K and T_c = 12.5 K, exhibits close to T_l a colossal magnetoresistivity (CMR). We quantitatively compare our data to recent theoretical work, which however fails to explain our observations. We attribute this disagreement with theory to the unique type of magnetic polaron formation in EuB_6.

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