We report on detailed magnetic measurements on the cubic helimagnet FeGe in external magnetic fields and temperatures near the onset of long-range magnetic order at T(C)=278.2(3) K. Precursor phenomena display a complex succession of temperature-driven crossovers and phase transitions in the vicinity of T(C). The A-phase region, present below T(C) and fields H<0.5 kOe, is split in several pockets. The complexity of the magnetic phase diagram is theoretically explained by the confinement of solitonic kinklike or Skyrmionic units that develop an attractive and oscillatory intersoliton coupling owing to the longitudinal inhomogeneity of the magnetization.

Weyl semimetals (WSMs) are topological quantum states wherein the electronic bands disperse linearly around pairs of nodes with fixed chirality, the Weyl points. In WSMs, nonorthogonal electric and magnetic fields induce an exotic phenomenon known as the chiral anomaly, resulting in an unconventional negative longitudinal magnetoresistance, the chiral-magnetic effect. However, it remains an open question to which extent this effect survives when chirality is not well-defined. Here, we establish the detailed Fermi-surface topology of the recently identified WSM TaP via combined angle-resolved quantum-oscillation spectra and band-structure calculations. The Fermi surface forms banana-shaped electron and hole pockets surrounding pairs of Weyl points. Although this means that chirality is ill-defined in TaP, we observe a large negative longitudinal magnetoresistance. We show that the magnetoresistance can be affected by a magnetic field-induced inhomogeneous current distribution inside the sample.

Eu 8 Ga 16 Ge 30 is the only clathrate known so far where the guest positions are fully occupied by a rare-earth element. Our investigations show that, in addition to the previously synthesized Eu 8 Ga 16 Ge 30 modification with clathrate-I structure, there exists a second modification with clathrate-VIII structure. Polycrystalline samples of both phases behave as local-moment ferromagnets with relatively low Curie temperatures ͑10.5 and 36 K͒. The charge-carrier concentrations are rather small ͑3.8 and 12.5ϫ10 20 cm Ϫ3 at 2 K͒ and, together with the low Curie temperatures, point to a semimetallic behavior. Both the specific heat and the thermal conductivity are consistent with the concept of guest atoms ''rattling'' in oversized host cages, leading to low thermal conductivities ͑''phonon glasses''͒. However, the electron mobilities are quite low, which, if intrinsic, would question the properties of an ''electron crystal'', commonly presumed in ''filled-cage'' materials. The dimensionless thermoelectric figure of merit reaches values of 0.01 at 100 K.

Hexagonal α-Ru trichloride single crystals exhibit a strong magnetic anisotropy and we show that upon applying fields up to 14 T in the honeycomb plane the successive magnetic order at T1 = 14 K and T2 = 8 K could be completely suppressed whereas in the perpendicular direction the magnetic order is robust. Furthermore the field dependence of χ(T) implies coexisting ferro-and antiferromagnetic exchange between in-plane components of Ru 3+ -spins, whereas for out-of-plane components a strong antiferromagnetic exchange becomes evident. 101 Ru zero-field nuclear magnetic resonance in the ordered state evidence a complex (probably non coplanar chiral) long-range magnetic structure. The large orbital moment on Ru 3+ is found in density-functional calculations. PACS numbers: 75.30.Gw, 75.40.Cx, Low dimensional 4d-and 5d-magnets show a wide variety of magnetic ground states due to crystal electric field (CEF) splitting in combination with a strong spin-orbit coupling (SOC). Especially the 5d 5 -iridate compounds earned great attention because of the predicted topological Mott insulating state due to the strong SOC and the Coulomb correlation [1]. Furthermore the strong SOC favors the asymmetric Dzyaloshinskii-Moriya (DM) interaction that often results in chiral spin arrangements in the ordered phases [2,3]. In addition, for spin-1/2 systems geometrical frustration of the magnetic exchange interactions frequently leads to a quantum spin-liquid ground state[4]. Among 4d-and 5d-systems, the Heisenberg-Kitaev model (HKM) was established to describe the competing bond-dependent magnetic exchange interactions in the honeycomb type of lattice structures [5]. Prominent examples are the 2-1-3 iridates (Li 2 IrO 3 , Na 2 IrO 3 ) where the magnetism is associated to the 5d 5 electrons on the Ir 4+ ions. According to the HKM, the phase diagram provides a transition from a conventional Neel-type of antiferromagnetic (AFM) order to a AFM stripy-(or zigzag-) type of order towards a pure quantum spin liquid (QSL) phase as a function of control parameter [6]. Indeed Na 2 IrO 3 shows an AFM order of zigzag-type at T = 15 K, whereas the Li 2 IrO 3 system is more close to the QSL regime and a non coplanar spiral order is discussed [7].In order to search for new 4d-or 5d-model system with the honeycomb lattice arrangement as a platform of HKM α-RuCl 3 turns out to be an excellent candidate because the low spin 3+ state of Ru (4d 5 ) is equivalent to the low spin 4+ state of Ir (5d 5 ). However, lowtemperature magnetic properties of α-RuCl 3 were not studied in detail and, so far, on powders only. Recently, Plumb and co-workers have shown in a spectroscopic experiment that α-RuCl 3 is a magnetic insulator due to sizable Coulomb correlations accompanied by the spinorbit coupling [8].In this Rapid Communication, we report detailed studies on the magnetic anisotropy by magnetization and specific heat on single crystals over a wide temperature and field range. Furthermore, we applied 99,101 Ru zero-field nuclear magnetic resonance as a local and ...

Platelike high-quality NaYbS2 rhombohedral single crystals with lateral dimensions of a few mm have been grown and investigated in great detail by bulk methods like magnetization and specific heat, but also by local probes like nuclear magnetic resonance (NMR), electron-spin resonance (ESR), muon-spin relaxation (µSR), and inelastic neutron scattering (INS) over a wide field and temperature range. Our single-crystal studies clearly evidence a strongly anisotropic quasi-2D magnetism and an emerging spin-orbit entangled S = 1/2 state of Yb towards low temperatures together with an absence of long-range magnetic order down to 260 mK. In particular, the clear and narrow Yb ESR lines together with narrow 23 Na NMR lines evidence an absence of inherent structural distortions in the system, which is in strong contrast to the related spin-liquid candidate YbMgGaO4 falling within the same space group R3m. This identifies NaYbS2 as a rather pure spin-1/2 triangular lattice magnet and a new putative quantum spin liquid.Introduction. -In low-dimensional quantum magnets, competing confined magnetic exchange interactions restrict the magnetic degrees of freedom, which leads to a strong frustration accompanied by enhanced quantum fluctuations. Ultimately this prevents the systems from longrange order, and the ground state is supposed to be a magnetic liquid. There are various types of such quantum spin liquids (QSL) depending on the lattice geometry (in 2D: square-, triangular-, kagome-, or honeycomb-type; in 3D: hyperkagome, hyperhoneycomb, or pyrochlore), the magnetic exchange (e.g. Heisenberg, Kitaev, or Dzyaloshinskii-Moriya type), and the magnetic ion itself [1][2][3][4]. Planar spin-1/2 triangular lattice magnets (TLMs) with antiferromagnetic exchange interactions are ideal QSL candidates as proposed by P. W. Anderson [5]. A few examples are found among the organic materials, such as K-(BEDT-TTF) 2 Cu 2 (CN) 3 [6] and EtnMe 4−n Sb[Pd(DMIT) 2 ] 2 [7], whereas among inorganic compounds such QSL model systems are very rare, e.g. Ba 3 CuSb 2 O 9 [8].

The discovery of materials with improved functionality can be accelerated by rational material design.1 Heusler compounds with tunable magnetic sublattices allow to implement this concept to achieve novel magnetic properties. 2 Here, we have designed a family of Heusler alloys with a compensated ferrimagnetic state. In the vicinity of the compensation composition in Mn-Pt-Ga, a giant exchange bias (EB) of more than 3 T and a similarly large coercivity are established. The large exchange anisotropy originates from the exchange interaction between the compensated host and ferrimagnetic clusters that arise from intrinsic anti-site disorder. We demonstrate the applicability of our design concept on a second material, Mn-1 Fe-Ga, with a magnetic transition above room temperature, exemplifying the universality of the concept and the feasibility of room-temperature applications. Our study points to a new direction for novel magneto-electronic devices. At the same time it suggests a new route for realizing rare-earth free exchange-biased hard magnets, where the second quadrant magnetization can be stabilized by the exchange bias.Exchange bias corresponds to a shift of the hysteresis loop of a ferromagnet along the magnetic field axis due to interfacial exchange coupling with an adjacent antiferromagnet. fully compensated magnet with a compensation point for a particular Mn/Pt ratio. This design scheme is schematically depicted in Fig. 1. From first-principles calculations, it follows that the critical composition with the zero magnetization is achieved in the solid solution Mn 3−x Pt x Ga at a Pt content of about x 0 = 0.59, which is in good agreement with the experimental findings. On optimizing the Mn/Pt ratio in Mn 3−x Pt x Ga, we always find a small lack of compensation in the material, due to the formation of FM clusters by anti-site disorder. This leads to an exceptionally large bulk EB and a large coercivity. In contrast to an artificial antiferromagnet, which is a thin film structure composed of two ferromagnetic layers separated by a coupling layer 9 , here we combine two isostructural ferrimagnetic compounds Mn 3 Ga and Mn 2 PtGa to obtain an intrinsically anisotropic compensated magnetic state on an atomic scale in a bulk material.In order to characterize the magnetic properties of Mn 3−x Pt x Ga we have measured the temperature dependence of the low field magnetization, M(T ). We find a systematic increase in the 4 ferrimagnetic Néel temperature (T N ) with increasing Mn content as shown in Fig. 2. The irreversibility between the ZFC and FC curves reflects the appearance of coercivity. We suggest that FM clusters embedded in the compensated host are the source of this irreversibility. NMR measurements confirm that these clusters originate from random swaps between Pt in the Mn-Pt planes and Mn in the Mn-Ga planes ( Supplementary Fig. 2). The irreversibility between ZFC and FC M(T ) curves increases with increasing magnetic field demonstrating that cooling in higher fields helps the FM clusters to grow in siz...

The ground state properties of CeFePO, a homologue of the new high temperature superconductors RFePnO1-xFx, were studied by means of susceptibility, specific heat, resistivity, and NMR measurements on polycrystals. All the results demonstrate that this compound is a magnetically nonordered heavy fermion metal with a Kondo temperature TK approximately 10 K, a Sommerfeld coefficient gamma=700 mJ/mol K2, and a mass enhancement factor of the order of 50. Analysis of the susceptibility data and of the spin relaxation time indicates that the strong electronic correlation effects originate from the Ce-4f electrons rather than from Fe-3d electrons. An enhanced Sommerfeld-Wilson ratio R=5.5 as well as a Korringa product S0/T1TK2 approximately 0.065 well below 1 indicate the presence of ferromagnetic correlations. Therefore, CeFePO appears to be on the nonmagnetic side of a ferromagnetic instability.

We report on 6,7 Li nuclear magnetic resonance measurements of the spin-chain compound LiCu2O2 in the paramagnetic and magnetically ordered states. Below T ≈24 K the NMR lineshape presents a clear signature of incommensurate (IC) static modulation of the local magnetic field consistent with an IC spiral modulation of the magnetic moments.7 Li NMR reveals strong phason-like dynamical fluctuations extending well below 24 K. We hypothesize that a series of phase transitions at 24.2, 22.5, and 9 K reflects a "Devil's staircase" type behavior generic for IC systems. LDA based calculations of exchange integrals reveal a large in-chain frustration leading to a magnetical spiral.Despite extensive efforts during the last decades spin ordering in frustrated S=1/2 quantum spin chains still remains a matter of broad activities. [1,2,3,4,5, 6] Rich phase diagrams with commensurate (C) and incommensurate (IC) phases, with spin-and charge ordering, dimerization, or superconductivity have been predicted. Most studies have been focused on various cuprates with corner-or edge-shared CuO 4 plaquettes. Edge-sharing of CuO 4 plaquettes leads to CuO 2 chains with a nearly 90• Cu-O-Cu bond angle causing a reduced nearest neighbor (nn) transfer and a next-nearest neighbor (nnn) transfer of similar size allowing frustration effects. IC spiral states driven by ferromagnetic (FM) nn exchange and in-chain frustration have been predicted theoretically for CuO 2 chain compounds such as Ca 2 Y 2 Cu 5 O 10 but discarded experimentally. [5, 6] The observation of in-chain IC effects in undoped quasi-1D cuprates is so far restricted by a sharp magnetic field driven C-IC transition observed in the spin-Peierls system CuGeO 3 at high magnetic fields. [7] Here we report on 6,7 Li nuclear magnetic resonance measurements (NMR) and local density (LDA) based analysis of the electronic and magnetic structure of the chain compound LiCu 2 O 2 . We show that the observed spontaneous magnetic order can be described by a spiral modulation of the magnetic moments. Independently, LDA calculations and a subsequent Heisenberganalysis reveal strong in-chain frustration driving spiral ordering in accord with the NMR data.LiCu 2 O 2 is an insulating orthorhombic compound [1,8,9, 10] with bilayers of edge-shared Cu 2+ -O chains running parallel to the b-axis separated by Cu 1+ planes. It exhibits a high-temperature antiferromagnetic(AFM)-like Curie-Weiss susceptibility χ(T ). Low-temperature χ(T ) and specific heat stufies [1,11] point to a series of intrinsic phase transitions at T ≈24.2 K, T ≈22.5 K, and T ≈9 K pointing to a complex multi-stage rearrangement of the spin structure. Magnetization studies performed in external fields up to 5 T did not reveal any signatures of field-induced transitions. µSR data[11] point to a broad distribution of magnetic fields at the muon stopping sites. LSDA(+U) calculations point to an FM in-chain ordering.[10] However, a simple FM ordering is in conflict with the µSR data[11] and the AFM dimer liquid picture. [1,12] Thus, to...