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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260407T110000
DTEND;TZID=Europe/Paris:20260407T120000
DTSTAMP:20260407T014805
CREATED:20260320T150306Z
LAST-MODIFIED:20260320T150310Z
UID:10000105-1775559600-1775563200@sfp-alpes.fr
SUMMARY:Rajeesh KUMAR N  (Research Associate\, Experimental Physics IV – Solid State Physics\, Ruhr-Universität Bochum\, Germany)
DESCRIPTION:Magnetism and spin dynamics of a weakly interacting rare-earth stretched diamond lattice\nRésumé : \nIn condensed matter physics\, a quantum-disordered ground state is characterized by the absence of long-range order down to absolute zero temperature\, where the disorder is driven by quantum fluctuations that persist even at T=0. On the other hand\, the magnetism of rare-earth materials is particularly intriguing as it originates from their localized 4f electrons\, which exhibit strong spin–orbit coupling\, pronounced magnetic anisotropy\, and relatively weak exchange interactions between magnetic ions. These unique characteristics\, when combined with suitable lattice geometry\, can give rise to a wide variety of unconventional magnetic ground states. \nA diamond magnetic lattice is a bipartite network and in its ideal form\, does not exhibit geometric frustration. However\, “stretched” diamond lattices have recently gained attention where frustration can emerge due to competition between nearest-neighbor (J1) and next-nearest-neighbor (J2) exchange interactions\, despite preserving the bipartite nature. In this context\, we investigate the magnetic ground state of the rare-earth molybdate compound Na5Yb(MoO4)4\, which crystallizes in a stretched diamond magnetic lattice. This compound can be viewed as a complex derivative of the conventional scheelite- type ABO4 structure\, crystallizing in the tetragonal space group I41/a. The magnetic lattice in Na5Yb(MoO4)4 is highly unusual\, featuring a remarkably large nearest-neighbor Yb–Yb separation of approximately 6.3 Å\, in contrast to previously studied stretched-diamond systems where the J1 distance typically lies in the range of 3–5 Å and is predominantly governed by superexchange interactions. Furthermore\, the next-nearest-neighbor (J2) Yb–Yb distance exceeds 9 Å\, significantly weakening the J2 exchange interactions. As a result\, magnetic frustration arising from competing J1–J2 exchange is significantly suppressed in Na5Yb(MoO4)4\, distinguishing it from other frustrated diamond-lattice systems. \nWe employ neutron and synchrotron X-ray diffraction to elucidate the structural details of Na5Yb(MoO4)4. The magnetic properties and ground state are investigated using bulk magnetic susceptibility measurements\, specific heat studies\, and muon spin relaxation (μSR) experiments. In addition\, density functional theory calculations within the DFT+U framework are used to provide theoretical support for the experimental findings. Our results establish Na5Yb(MoO4)4 as a rare example of a dipolar quantum paramagnet in which single-ion physics and long-range dipolar interactions dominate\, while exchange interactions are suppressed to the millikelvin energy scale. \nReference \n1. N. D. Kelly et al.\, Physical Review Materials 6\, 044410 (2022).\n2. A. Chauhan et al.\, Physical Review B 108\, 134424 (2023).\n3. J. Kumar et al.\, Physical Review B 111\, 014411 (2025).\n4. T. Arh et al.\, Nat. Mater. 21\, 416 (2022). \n  \nCollege 5B Secretary \nAlberto Rodriguez Velamazan \nExternal visitors may ask for a site access to Brigitte Dubouloz (dubouloz@ill.fr)
URL:https://sfp-alpes.fr/event/rajeesh-kumar-n-research-associate-experimental-physics-iv-solid-state-physics-ruhr-universitat-bochum-germany/
LOCATION:ILL – Salle de Séminaire (110-111)\, ILL 50 71 avenue des Martyrs\, Grenoble\, 38042\, France
CATEGORIES:Séminaire
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260408T093000
DTEND;TZID=Europe/Paris:20260408T113000
DTSTAMP:20260407T014805
CREATED:20260402T160829Z
LAST-MODIFIED:20260402T160835Z
UID:10000120-1775640600-1775647800@sfp-alpes.fr
SUMMARY:Soutenance d'HDR de Marie-Aude MEASSON (Institut Néel\, équipe MagSup)
DESCRIPTION:Matériaux Quantiques en Conditions Extrêmes : Modes Collectifs et Ordres Quantiques Exotiques\nRésumé : A VENIR… \nPrésentation en français \n_ \nContact : marie-aude.measson@neel.cnrs.fr
URL:https://sfp-alpes.fr/event/soutenance-dhdr-de-marie-aude-measson-institut-neel-equipe-magsup/
LOCATION:CNRS – Bâtiment A\, CNRS - Institut Néel 25 avenue des Martyrs\, Grenoble\, 38054\, France
CATEGORIES:Soutenance,Soutenance HDR
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260408T140000
DTEND;TZID=Europe/Paris:20260408T150000
DTSTAMP:20260407T014805
CREATED:20260320T150834Z
LAST-MODIFIED:20260320T151400Z
UID:10000106-1775656800-1775660400@sfp-alpes.fr
SUMMARY:Javier CAMPO (Aragón Nanoscience and Materials Institute (CSIC - Universidad de Zaragoza)  Zaragoza\, Spain)
DESCRIPTION:A new magnetic state\, “B-Phase”\, found in MnSi at Low Temperatures \nRésumé : \nIn cubic chiral magnets\, Dzyaloshinskii-Moriya (DM) interactions within the chiral crystal structure result in diverse magnetic textures\, including skyrmion lattices (SkL) and chiral soliton lattices\, which hold promise for spintronic and magnonic devices. Among these\, MnSi has been extensively studied due to the SkL formation in the so-called “A-phase” just below Tc [1].  Recently\, it was suggested theoretically that at low temperatures (T)\, the conical helimagnetic (CH) and forced-ferromagnetic (FFM) phases in MnSi might not be directly connected but separated by another SkL phase\, possibly metastable\, or a new phase of unknown nature near the critical magnetic field (Bc) [2]. The theoretical prediction of the new SkL phase at low T is in good agreement with the experiments reported in MnSi and Cu2OSeO3 [3\,4]. On the other hand\, by using careful ac susceptibility measurements at low temperature\, we determined the magnetic phase diagrams of oriented crystals of MnSi [5]. A new unexpected region\, termed “B-phase”\, was observed when the magnetic field was applied along the main diagonal <111>. \nTo clarify the nature of the “B-phase”\, we performed small-angle neutron scattering (SANS) measurements at TAIKAN in J-PARC and transverse field (TF)-μSR experiments at TRIUMF. At low temperatures and fields near Bc\, SANS patterns revealed two peaks along the horizontal axis\, corresponding to the magnetic Bragg peaks of the CH state. Notably\, no diffraction peaks indicative of a six-fold-symmetric SkL were observed. Meanwhile\, μSR results showed a distinct internal magnetic field distribution in the “B-phase”\, different from those in the CH or FFM phases\, suggesting that the “B-phase” could involve a reorientation of Mn helices within the unit cell. \nIn the presentation\, we will discuss these SANS and μSR findings in detail and their implications for understanding the spin texture in the “B-phase”. \nReferences \n\nS. Mühlbauer et al.\, Science 323\, 915 (2009).\nV. Laliena and J. Campo\, Phys. Rev. B 96\, 134420 (2017).\nT. Nakajima et al.\, Sci. Adv. 3\, e1602562 (2017).\nA. Chacon et al.\, Nature Phys 14\, 936–941 (2018).\nM. Ohkuma et al.\, APL Mater. 10\, 041104 (2022).\n\n  \nCollege 5B Secretary \nAlberto Rodriguez Velamazan \nExternal visitors may ask for a site access to Brigitte Dubouloz (dubouloz@ill.fr)
URL:https://sfp-alpes.fr/event/javier-campo-aragon-nanoscience-and-materials-institute-csic-universidad-de-zaragoza-zaragoza-spain/
LOCATION:ILL – Salle de Séminaire (110-111)\, ILL 50 71 avenue des Martyrs\, Grenoble\, 38042\, France
CATEGORIES:Séminaire
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260409T140000
DTEND;TZID=Europe/Paris:20260409T150000
DTSTAMP:20260407T014805
CREATED:20260320T151906Z
LAST-MODIFIED:20260320T151906Z
UID:10000107-1775743200-1775746800@sfp-alpes.fr
SUMMARY:Gonzalo PEREZ-BLASCO  (Aragón Nanoscience and Materials Institute (CSIC - Universidad de Zaragoza) - Physics Condensed Matter Dept. Zaragoza\, Spain)
DESCRIPTION:Empirical machine learning for 3He spin-filter polarisation decay\nRésumé : \nA lightweight\, empirical machine-learning framework is presented for predicting the time evolution of the nuclear polarisation of 3He spin-filter cells under realistic neutron beam line conditions. The method bridges the gap between detailed microscopic modelling of polarisation relaxation and purely heuristic correction schemes by combining supervised learning with basic physics-informed constraints on spin relaxation. This strategy ensures physically consistent polarisation forecasts while maintaining computational efficiency and ease of implementation. \nThe framework is tailored to the limited number of heterogeneous experimental datasets typically encountered during routine instrument operation. Rather than explicitly modelling all relaxation mechanisms\, it learns an effective representation of polarisation decay directly from experimental data. Within the domain spanned by the training dataset\, the model demonstrates stable predictive performance while preserving the expected exponential relaxation behaviour and accommodating non-linear\, history-dependent effects. \nThe resulting predictions enable reliable\, time-dependent corrections of neutron scattering data affected by polarisation efficiency drift. Compared with traditional single-parameter relaxation models\, the approach accounts for the combined influence of multiple experimental parameters and their temporal evolution. Although extrapolation beyond the training domain requires careful validation\, the method provides an operationally efficient and reproducible tool for polarisation monitoring and correction in realistic experimental environments. \n  \nCollege 6 Secretary \nGabriel Cuello \nExternal visitors may ask for a site access to Brigitte Dubouloz (dubouloz@ill.fr)
URL:https://sfp-alpes.fr/event/gonzalo-perez-blasco-aragon-nanoscience-and-materials-institute-csic-universidad-de-zaragoza-physics-condensed-matter-dept-zaragoza-spain/
LOCATION:ILL – Salle de Séminaire (110-111)\, ILL 50 71 avenue des Martyrs\, Grenoble\, 38042\, France
CATEGORIES:Séminaire
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