We present an investigation of the influence of low levels of chemical substitution on the magnetic ground state and Néel skyrmion lattice (SkL) state in GaV 4 S 8-y Se y , where y = 0, 0.1, 7.9, and 8. Muon-spin spectroscopy (μSR) measurements on y = 0 and 0.1 materials reveal the magnetic ground state consists of microscopically coexisting incommensurate cycloidal and ferromagnetic environments, whereas chemical substitution leads to the growth of localized regions of increased spin density. μSR measurements of emergent low-frequency skyrmion dynamics show that the SkL exists under low levels of substitution at both ends of the series. Skyrmionic excitations persist to temperatures below the equilibrium SkL in substituted samples, suggesting the presence of skyrmion precursors over a wide range of temperatures.

Citation for published item:prnkeD u¡ evin tF eF nd ruddrtD fenjmin wF nd rikenD homs tF nd ioD pn nd flundellD tephen tF nd rttD prnis vF nd grisntiD wrt nd frkerD toel eF F nd glrkD tewrt tF nd § tefn § i § D ele § s nd rtnenD woni giomg nd flkrishnnD qeeth nd vnsterD om @PHIVA 9wgneti phses of skyrmionEhosting qRVyey @y a HD PD RD VA proed with muon spetrosopyF9D hysil review fFD WV @SAF HSRRPVF Further information on publisher's website: eprinted with permission from the emerin hysil oietyX prnkeD u¡ evin tF eFD ruddrtD fenjmin wFD rikenD homs tFD ioD pnD flundellD tephen tFD rttD prnis vFD grisntiD wrtD frkerD toel eF FD glrkD tewrt tFD § tefn § i § D ele § sD rtnenD woni giomgD flkrishnnD qeeth vnsterD om @PHIVAF wgneti phses of skyrmionEhosting qRVyey @y a HD PD RD VA proed with muon spetrosopyF hysil eview f WV@SAX HSRRPVF @PHIVA 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 oietyFAdditional 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 present the results of a muon-spin spectroscopy investigation of GaV 4 S 8−y Se y with y = 0, 2, 4, and 8. Zero-field measurements suggest that GaV 4 Se 8 and GaV 4 S 8 have distinct magnetic ground states, with the latter material showing an anomalous temperature dependence of the local magnetic field. It is not possible to evolve the magnetic state continuously between these two systems, with the intermediate y = 2 and 4 materials showing glassy magnetic behavior at low temperature. The skyrmion lattice (SkL) phase is evident in the y = 0 and 8 materials through an enhanced response of the muon-spin relaxation to the emergent dynamics that accompany the SkL. For our polycrystalline samples of GaV 4 Se 8 , this enhanced dynamic response is confined to a smaller region of the magnetic field-temperature phase diagram than the previous reports of the SkL in single crystals.

We present an investigation into the structural and magnetic properties of Zn-substituted Cu 2 OSeO 3 , a system in which the skyrmion lattice (SkL) phase in the magnetic field-temperature phase diagram was previously seen to split as a function of increasing Zn concentration. We find that splitting of the SkL is only observed in polycrystalline samples and reflects the occurrence of several coexisting phases with different Zn content, each distinguished by different magnetic behavior. No such multiphase behavior is observed in single-crystal samples.

We report small angle X-ray scattering (SAXS) measurements of the skyrmion lattice in two 200 nm thick Cu2OSeO3 lamellae aligned with the applied magnetic field parallel to the out of plane [110] or [100] crystallographic directions. Our measurements show that the equilibrium skyrmion phase in both samples is expanded significantly compared to bulk crystals, existing between approximately 30 and 50 K over a wide region of magnetic field. This skyrmion state is elliptically distorted at low fields for the [110] sample, and symmetric for the [100] sample, possibly due to crystalline anisotropy becoming more important at this sample thickness than it is in bulk samples. Furthermore, we find that a metastable skyrmion state can be observed at low temperature by field cooling through the equilibrium skyrmion pocket in both samples. In contrast to the behavior in bulk samples, the volume fraction of metastable skyrmions does not significantly depend on cooling rate. We show that a possible explanation for this is the change in the lowest temperature of the skyrmion state in this lamellae compared to bulk, without requiring different energetics of the skyrmion state. arXiv:1909.07855v1 [cond-mat.str-el]

The molecular coordination complex NiI2(3,5-lut)4 [where (3,5-lut) = (3,5-lutidine) = (C7H9N)] has been synthesized and characterized by several techniques including synchrotron X-ray diffraction, ESR, SQUID magnetometry, pulsed-field magnetization, inelastic neutron scattering and muon spin relaxation. Templated by the configuration of 3,5-lut ligands the molecules pack in-registry with the Ni-I· · · I-Ni chains aligned along the c-axis. This arrangement leads to through-space I· · · I magnetic coupling which is directly measured for the first time in this work. The net result is a near-ideal realization of the S = 1 Haldane chain with J = 17.5 K and energy gaps of ∆ = 5.3 K ∆ ⊥ = 7.7 K, split by the easy-axis single-ion anisotropy D = −1.2 K. The ratio D/J = −0.07 affords one of the most isotropic Haldane systems yet discovered, while the ratio ∆0/J = 0.40(1) (where ∆0 is the average gap size) is close to its ideal theoretical value, suggesting a very high degree of magnetic isolation of the spin chains in this material. The Haldane gap is closed by orientation-dependent critical fields µ0H c = 5.3 T and µ0H ⊥ c = 4.3 T, which are readily accessible experimentally and permit investigations across the entirety of the Haldane phase, with the fully polarized state occurring at µ0H s = 46.0 T and µ0H ⊥ s = 50.7 T. The results are explicable within the so-called fermion model, in contrast to other reported easy-axis Haldane systems. Zero-field magnetic order is absent down to 20 mK and emergent end-chain effects are observed in the gapped state, as evidenced by detailed low-temperature measurements. arXiv:1909.07900v1 [cond-mat.str-el]

We present longitudinal-field muon-spin relaxation (LF μSR) measurements on two systems that stabilize a skyrmion lattice (SkL): Cu 2 OSeO 3 , and Co x Zn y Mn 20−x−y for (x, y) = (10, 10), (8, 9), and (8, 8). We find that the SkL phase of Cu 2 OSeO 3 exhibits emergent dynamic behavior at megahertz frequencies, likely due to collective excitations, allowing the SkL to be identified from the μSR response. From measurements following different cooling protocols and calculations of the muon stopping site, we suggest that the metastable SkL is not the majority phase throughout the bulk of this material at the fields and temperatures where it is often observed. The dynamics of bulk Co 8 Zn 9 Mn 3 are well described by 2 GHz excitations that reduce in frequency near the critical temperature, while in Co 8 Zn 8 Mn 4 we observe similar behavior over a wide range of temperatures, implying that dynamics of this kind persist beyond the SkL phase.

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