We present a comprehensive study of the evolution of the nematic electronic structure of FeSe using high resolution angle-resolved photoemission spectroscopy (ARPES), quantum oscillations in the normal state and elastoresistance measurements. Our high resolution ARPES allows us to track the Fermi surface deformation from four-fold to two-fold symmetry across the structural transition at ~87 K which is stabilized as a result of the dramatic splitting of bands associated with dxz and dyz character. The low temperature Fermi surface is that a compensated metal consisting of one hole and two electron bands and is fully determined by combining the knowledge from ARPES and quantum oscillations. A manifestation of the nematic state is the significant increase in the nematic susceptibility as approaching the structural transition that we detect from our elastoresistance measurements on FeSe. The dramatic changes in electronic structure cannot be explained by the small lattice effects and, in the absence of magnetic fluctuations above the structural transition, points clearly towards an electronically driven transition in FeSe stabilized by orbital-charge ordering.Comment: Latex, 8 pages, 4 figure

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We present the results of high-field magnetization and muon-spin relaxation measurements on the coordination polymer CuF2(H2O)2(pyrazine) in pressures up to 22.5 kbar. We observe a transition from a quasi-two-dimensional to a quasi-one-dimensional antiferromagnetic phase at 9.1 kbar, driven by a rotation of the Jahn-Teller axis. Long-range antiferromagnetic ordering is seen in both regimes, as well as a phase separation in the critical pressure region. The magnetic dimensionality switching as pressure is increased is accompanied by a halving of the primary magnetic exchange energy J and a fivefold decrease in the ordering temperature TN. J decreases gradually with pressure in the two-dimensional phase, and then increases in the one-dimensional regime. We relate both effects to the changes in the crystal structure with applied pressure.

[Ni(HF(2))(3-Clpy)(4)]BF(4) (py = pyridine) is a simple one-dimensional (1D) coordination polymer composed of compressed NiN(4)F(2) octahedra that form chains with bridging HF(2)(-) ligands. In spite of significant distortion of the HF(2)(-) bridge, a quasi-1D antiferromagnetic (AFM) behavior was observed with J(FHF) = 4.86 K.

Citation for published item:vnsterD F nd qoddrdD FeF nd flundellD FtF nd porondD pFF nd qhnndzdehD F nd w¤ ollerD tFF nd fkerD FtF nd rttD pFvF nd finesD gF nd rungD vF nd osnitzD tF nd whonldD FhF nd wodiD uFeF nd ingletonD tF nd oppingD gFF nd feleD FeFF nd ioD pF nd hlueterD tFeF nd frtonD eFwF nd grerD FhF nd grreiroD uFiF nd rnD rFiF nd wnsonD tFvF @PHIRA 9gontrolling mgneti order nd quntum disorder in moleuleEsed mgnetsF9D hysil review lettersFD IIP @PHAF pF PHUPHIF Further information on publisher's website: eprinted with permission from the emerin hysil oietyX F vnsterD FeF qoddrdD FtF flundellD pFF porondD F qhnndzdehD tFF w¤ ollerD FtF fkerD pFvF rttD gF finesD vF rungD tF osnitzD FhF whonldD uFeF wodiD tF ingletonD gFF oppingD FeFF feleD pF ioD tFeF hlueterD eFwF frtonD FhF grerD uFiF grreiroD rFiF rnD nd tFvF wnsonD hysil eview vettersD IIPD PHD PHUPHID PHIRF PHIR y the emerin hysil oietyF eders my viewD rowseD ndGor downlod mteril for temporry opying purposes onlyD provided these uses re for nonommeril personl purposesF ixept s provided y lwD this mteril my not e further reproduedD distriutedD trnsmittedD modi(edD dptedD performedD displyedD pulishedD or sold in whole or prtD without prior written permission from the emerin hysil oietyF Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We investigate the structural and magnetic properties of two molecule-based magnets synthesized from the same starting components. Their different structural motifs promote contrasting exchange pathways and consequently lead to markedly different magnetic ground states. Through examination of their structural and magnetic properties we show that ½CuðpyzÞðH 2 OÞðglyÞ 2 ðClO 4 Þ 2 may be considered a quasi-onedimensional quantum Heisenberg antiferromagnet whereas the related compound ½CuðpyzÞðglyÞðClO 4 Þ, which is formed from dimers of antiferromagnetically interacting Cu 2þ spins, remains disordered down to at least 0.03 K in zero field but shows a field-temperature phase diagram reminiscent of that seen in materials showing a Bose-Einstein condensation of magnons.

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We present a novel susceptometer with a particularly small spatial footprint and no moving parts. The susceptometer is suitable for use in systems with limited space where magnetic measurements may not have been previously possible, such as in pressure cells and rotators, as well as in extremely high pulsed fields. The susceptometer is based on the proximity detector oscillator, which has a broad dynamic resonant frequency range and has so far been used predominantly for transport measurements. We show that for insulating samples, the resonance frequency behavior as a function of field consists of a magnetoresistive and an inductive component, originating, respectively, from the sensor coil and the sample. The response of the coil is modeled, and upon subtraction of the magnetoresistive component the dynamic magnetic susceptibility and magnetization can be extracted. We successfully measure the magnetization of the organic molecular magnets Cu(H(2)O)(5)(VOF(4))(H(2)O) and [Cu(HF(2))(pyz)(2)]BF(4) in pulsed magnetic fields and by comparing the results to that from a traditional extraction susceptometer confirm that the new system can be used to measure and observe magnetic susceptibilities and phase transitions.

We report the temperature T and magnetic field H dependence of the thermopower S of an itinerant triangular antiferromagnet PdCrO 2 in high magnetic fields up to 32 T. In the paramagnetic phase, the zerofield thermopower is positive with a value typical of good metals with a high carrier density. In marked contrast to typical metals, however, S decreases rapidly with increasing magnetic field, approaching zero at the maximum field scale for T > 70 K. We argue here that this profound change in the thermoelectric response derives from the strong interaction of the 4d correlated electrons of the Pd ions with the shortrange spin correlations of the Cr 3þ spins that persist beyond the Néel ordering temperature due to the combined effects of geometrical frustration and low dimensionality. DOI: 10.1103/PhysRevLett.116.087202 The interplay between itinerant electrons and even simple magnetic structures can lead to spectacular effects, the giant magnetoresistance seen in magnetic multilayers being arguably the most prominent example [1]. In geometrically frustrated magnets, complex spin textures that couple to the conduction electrons create an altogether different landscape, where short-range correlations are expected to play a major role. Moreover, since magnetism in metals can be destabilized much more readily than in insulators, magnetic frustration in metallic systems offers a rich playground to search for the emergence of novel transport phenomena. Notable recent examples include the unconventional anomalous Hall effect (AHE) observed in magnetic pyrochlores [2,3] and the suppression of thermopower in a longitudinal magnetic field in the layered Curie-Weiss metal Na x CoO 2 [4].Despite their obvious potential for new physics, metallic frustrated magnets have been noticeably less studied than their insulating counterparts, largely due to the fact that such materials are rare. Of particular interest are materials in which the conduction electrons and magnetic moments arise from different subsystems. In this context, the quasi-two-dimensional (quasi-2D) antiferromagnet PdCrO 2 [4-6] is somewhat unique. PdCrO 2 has a delafossite crystal structure with layers of Pd ions arranged in a triangular lattice stacked between magnetic edgesharing CrO 6 octahedra. The latter contains Cr 3þ ions with localized (Mott insulating) 3=2 spins which order in the 120°antiferromagnetic (AFM) structure below T N ¼ 37.5 K [7,8]. The frustration parameter f, defined as an absolute ratio of the Weiss temperature Θ W and the ordering temperature T N , is around 13 for PdCrO 2 , indicating a high level of frustration [7][8][9]. According to band structure calculations [10], angle-resolved photoemission [10], and quantum oscillation (QO) studies [11,12],