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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...

High-quality single crystals of NaYbSe2, which resembles a perfect triangular-lattice antiferromagnet without the intrinsic disorder, are investigated by magnetization and specific-heat, as well as the local probe techniques nuclear magnetic resonance (NMR) and electron spin resonance (ESR). The low-field measurements confirm the absence of any spin freezing or long-range magnetic order down to 50 mK, which suggests a quantum spin liquid ground (QSL) state with gapless excitations. Instability of the QSL state is observed upon applying magnetic fields. For the H⊥c direction, a field-induced magnetic phase transition is observed above 2 T from the Cp(T ) data, agreeing with a clear Ms 3 plateau of M (H), which is associated with an up-up-down (uud) spin arrangement. For the H c direction, a field-induced transition could be evidenced at a much higher field range (9 -21 T). The 23 Na NMR measurements provide microscopic evidence for field-induced ordering for both directions. A reentrant behaviour of TN, originating from the thermal and quantum spin fluctuations, is observed for both directions. The anisotropic exchange interactions J ⊥ 4.7 K and Jz 2.33 K are extracted from the modified bond-dependent XXZ model for the spin-1 2 triangular-lattice antiferromagnet. The absence of magnetic long-range order at zero fields is assigned to the effect of strong bond-frustration, arising from the complex spin-orbit entangled 4f ground state. Finally, we derive the highly anisotropic magnetic phase diagram, which is discussed in comparison with the existing theoretical models for spin-1 2 triangular-lattice antiferromagnets. :1911.12712v1 [cond-mat.str-el] arXiv

We report a large exchange-bias effect after zero-field cooling the new tetragonal Heusler compound Mn(2)PtGa from the paramagnetic state. The first-principles calculation and the magnetic measurements reveal that Mn(2)PtGa orders ferrimagnetically with some ferromagnetic inclusions. We show that ferrimagnetic ordering is essential to isothermally induce the exchange anisotropy needed for the zero-field cooled exchange bias during the virgin magnetization process. The complex magnetic behavior at low temperatures is characterized by the coexistence of a field-induced irreversible magnetic behavior and a spin-glass-like phase. The field-induced irreversibility originates from an unusual first-order ferrimagnetic to antiferromagnetic transition, whereas the spin-glass-like state forms due to the existence of antisite disorder intrinsic to the material.

We report markedly different transport properties of ABA- and ABC-stacked trilayer graphenes. Our experiments in double-gated trilayer devices provide evidence that a perpendicular electric field opens an energy gap in the ABC trilayer, while it causes the increase of a band overlap in the ABA trilayer. In a perpendicular magnetic field, the ABA trilayer develops quantum Hall plateaus at filling factors of \nu = 2, 4, 6... with a step of \Delta \nu = 2, whereas the inversion symmetric ABC trilayer exhibits plateaus at \nu = 6 and 10 with 4-fold spin and valley degeneracy.Comment: 4 pages, 4 figure

Topological materials ranging from topological insulators to Weyl and Dirac semimetals form one of the most exciting current fields in condensed-matter research. Many half-Heusler compounds, RPtBi (R = rare earth), have been theoretically predicted to be topological semimetals. Among various topological attributes envisaged in RPtBi, topological surface states, chiral anomaly, and planar Hall effect have been observed experimentally. Here, we report an unusual intrinsic anomalous Hall effect (AHE) in the antiferromagnetic Heusler Weyl semimetal compounds GdPtBi and NdPtBi that is observed over a wide temperature range. In particular, GdPtBi exhibits an anomalous Hall conductivity of up to 60 Ω⋅cm and an anomalous Hall angle as large as 23%. Muon spin-resonance (μSR) studies of GdPtBi indicate a sharp antiferromagnetic transition () at 9 K without any noticeable magnetic correlations above Our studies indicate that Weyl points in these half-Heuslers are induced by a magnetic field via exchange splitting of the electronic bands at or near the Fermi energy, which is the source of the chiral anomaly and the AHE.

We have studied the thermodynamic properties of single-crystalline TbFe3(BO3)4. Magnetization measurements have been carried out as a function of magnetic field (up to 50 T) and temperature up to 350 K with the magnetic field both parallel and perpendicular to the trigonal c-axis of the crystal. The specific heat has been measured in the temperature range 2-300 K with a magnetic field up to 9 T applied parallel to the c-axis. The data indicate a structural phase transition at 192 K and antiferromagnetic spin ordering at TN ≈ 40 K. A Schottky anomaly is present in the specific heat data around 20 K, arising due to two low-lying energy levels of the Tb 3+ ions being split by f-d coupling. Below T N magnetic fields parallel to the c-axis drive a spin-flop phase transition, which is associated with a large magnetization jump. The highly anisotropic character of the magnetic susceptibility is ascribed mainly to the Ising-like behavior of the Tb 3+ ions in the trigonal crystal field. We describe our results in the framework of an unified approach which is based on mean-field approximation and crystal-field calculations.

Sr3Cr2O8 consist of a lattice of spin-1/2 Cr 5+ ions, which form hexagonal bilayers and which are paired into dimers by the dominant antiferromagnetic intrabilayer coupling. The dimers are coupled three-dimensionally by frustrated interdimer interactions. A structural distortion from hexagonal to monoclinic leads to orbital order and lifts the frustration giving rise to spatially anisotropic exchange interactions. We have grown large single crystals of Sr3Cr2O8 and have performed DC susceptibility, high field magnetisation and inelastic neutron scattering measurements. The neutron scattering experiments reveal three gapped and dispersive singlet to triplet modes arising from the three twinned domains that form below the transition thus confirming the picture of orbital ordering. The exchange interactions are extracted by comparing the data to a Random Phase Approximation model and the dimer coupling is found to be J0 = 5.55 meV, while the ratio of interdimer to intradimer exchange constants is J ′ /J0 = 0.64. The results are compared to those for other gapped magnets.