Magnetic diffuse scattering in artificial kagome spin ice

This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevB.93.224413The study of magnetic correlations in dipolar-coupled nanomagnet systems with synchrotron x-ray scattering provides a means to uncover emergent phenomena and exotic phases, in particular in systems with thermally active magnetic moments. From the diffuse signal of soft x-ray resonant magnetic scattering, we have measured magnetic correlations in a highly dynamic artificial kagome spin ice with sub-70-nm Permalloy nanomagnets. On comparing experimental scattering patterns with Monte Carlo simulations based on a needle-dipole model, we conclude that kagome ice I phase correlations exist in our experimental system even in the presence of moment fluctuations, which is analogous to bulk spin ice and spin liquid behavior. In addition, we describe the emergence of quasi-pinch-points in the magnetic diffuse scattering in the kagome ice I phase. These quasi-pinch-points bear similarities to the fully developed pinch points with singularities of a magnetic Coulomb phase, and continually evolve into the latter on lowering the temperature. The possibility to measure magnetic diffuse scattering with soft x rays opens the way to study magnetic correlations in a variety of nanomagnetic systems.Seventh Framework Programme (Grant ID: 290605

Thermodynamic phase transitions in a frustrated magnetic metamaterial

The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 290605 (COFUND: PSI-FELLOW) and from the EPSRC (grant EP/J01060X).Materials with interacting magnetic degrees of freedom display a rich variety of magnetic behaviour that can lead to novel collective equilibrium and out-of-equilibrium phenomena. In equilibrium, thermodynamic phases appear with the associated phase transitions providing a characteristic signature of the underlying collective behaviour. Here we create a thermally active artificial kagome spin ice that is made up of a large array of dipolar interacting nanomagnets and undergoes phase transitions predicted by microscopic theory. We use low energy muon spectroscopy to probe the dynamic behaviour of the interacting nanomagnets and observe peaks in the muon relaxation rate that can be identified with the critical temperatures of the predicted phase transitions. This provides experimental evidence that a frustrated magnetic metamaterial can be engineered to admit thermodynamic phases.Publisher PDFPeer reviewe

Continuous magnetic phase transition in artificial square ice

Critical behavior is very common in many fields of science and a wide variety of many- body systems exhibit emergent critical phenomena. The beauty of critical phase transitions lies in their scale-free properties, such that the temperature dependence of physical parameters of systems differing at the microscopic scale can be described by the same generic power laws. In this work we establish the critical properties of the antiferromagnetic phase transition in artificial square ice, showing that it belongs to the two-dimensional Ising universality class, which extends the applicability of such concepts from atomistic to mesoscopic magnets. Combining soft x-ray resonant magnetic scattering experiments and Monte Carlo simulations, we characterize the transition to the low-temperature long-range order expected for the artificial square-ice system. By measuring the critical scattering, we provide direct quantitative evidence of a continuous magnetic phase transition, obtaining critical exponents which are compatible with those of the two-dimensional Ising universality class. In addition, by varying the blocking temperature relative to the phase transition temperature, we demonstrate its influence on the out-of-equilibrium dynamics due to critical slowing down at the phase transition

Measurement of the atmospheric muon depth intensity relation with the NEMO Phase-2 tower

The results of the analysis of the data collected with the NEMO Phase-2 tower, deployed at 3500 m depth about 80 km off-shore Capo Passero (Italy), are presented. Cherenkov photons detected with the photomultipliers tubes were used to reconstruct the tracks of atmospheric muons. Their zenith-angle distribution was measured and the results compared with Monte Carlo simulations. An evaluation of the systematic effects due to uncertainties on environmental and detector parameters is also included. The associated depth intensity relation was evaluated and compared with previous measurements and theoretical predictions. With the present analysis, the muon depth intensity relation has been measured up to 13 km of water equivalent.Comment: submitted to Astroparticle Physic

Long term monitoring of the optical background in the Capo Passero deep-sea site with the NEMO tower prototype

The NEMO Phase-2 tower is the first detector which was operated underwater for more than 1 year at the "record" depth of 3500 m. It was designed and built within the framework of the NEMO (NEutrino Mediterranean Observatory) project. The 380 m high tower was successfully installed in March 2013 80 km offshore Capo Passero (Italy). This is the first prototype operated on the site where the Italian node of the KM3NeT neutrino telescope will be built. The installation and operation of the NEMO Phase-2 tower has proven the functionality of the infrastructure and the operability at 3500 m depth. A more than 1 year long monitoring of the deep water characteristics of the site has been also provided. In this paper the infrastructure and the tower structure and instrumentation are described. The results of long term optical background measurements are presented. The rates show stable and low baseline values, compatible with the contribution of K-40 light emission, with a small percentage of light bursts due to bioluminescence. All these features confirm the stability and good optical properties of the site.Funded by SCOAP3Adrián Martínez, S.; Aiello, S.; Ameli, F.; Anghinolfi, M.; Ardid Ramírez, M.; Barbarino, G.; Barbarito, E.... (2016). Long term monitoring of the optical background in the Capo Passero deep-sea site with the NEMO tower prototype. European Physical Journal C: Particles and Fields. 76(68):1-11. https://doi.org/10.1140/epjc/s10052-016-3908-0S1117668M. Ageron et al., ANTARES: the first undersea neutrino telescope. Nucl. Instr. Methods A 656, 11 (2011)V. Aynutdnov for the Baikal Coll., The BAIKAL neutrino project: results and perspective. Nucl. Instr. Methods. A 628, 115 (2011)A. Achterberg et al., First year performance of the IceCube neutrino telescope. Astropart. Phys. 26, 155 (2006)M.G. 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Methods A 487, 423 (2002)G. Riccobene et al., Deep seawater inherent optical properties in the Southern Ionian Sea. Astropart. Phys. 27, 1 (2007)A. Rubino et al., Abyssal undular vortices in the Eastern Mediterranean basin. Nat. Commun. 3, 834 (2012)KM3NeT web site. www.km3net.orgM. Sedita for the NEMO collaboration, Electro-optical cable and power feeding system for the NEMO Phase-2 project. Nucl. Instr. Methods A 567, 531 (2006)R. Cocimano for the NEMO collaboration, A comparison of AC and DC power feeding systems based on the NEMO experiences. Nucl. Instr. Methods A 602, 171 (2009)A. Orlando for the NEMO collaboration, On line monitoring of the power control and engineering parameters systems of the NEMO Phase-2 tower. Nucl. Instr. Methods. A 602, 180 (2009)M. Musumeci for the NEMO collaboration, Construction and deployment issues for a km {3} 3 underwater detector. Nucl. Instr. Methods. A 567, 545 (2006)S. Aiello et al., The optical modules of the phase-2 of the NEMO project. JINST 8, P07001 (2013)E. Leonora, S. Aiello, Design and assembly of the optical modules for phase-2 of the NEMO project. Nucl. Instr. Methods A 725, 234 (2013)S. Aiello et al., Procedures and results of the measurements on large area photomultipliers for the NEMO project. Nucl. Instr. Methods A 614, 206 (2010)C.A. Nicolau for the NEMO collaboration, An FPGA-based readout electronics for neutrino telescopes. Nucl. Instr. Methods A 567, 552 (2006)M. Cordelli et al., PORFIDO: oceanographic data for neutrino telescopes. Nucl. Instr. Methods A 626–627, S109 (2011)F. Ameli, The data acquisition and transport design for NEMO Phase-1. IEEE Trans. Nucl. Sci. 55(1), 233 (2008)A. D’Amico for the NEMO collaboration, Design of the optical Raman amplifier for the shore station of NEMO Phase-2. Nucl. Instr. Methods A 626–627, S173 (2011)T. Chiarusi for the NEMO collaboration, Scalable TriDAS for the NEMO project. Nucl. Instr. Methods A 630, 107 (2011)S. Viola et al., NEMO-SMO acoustic array: a deep-sea test of a novel acoustic positioning system for a km $$^3$$ 3 -scale underwater neutrino telescope. Nucl. Instr. Methods A 725, 207 (2013)S. Viola et al., in Underwater acoustic positioning system for the SMO and KM3NeT-Italia projects. AIP Conference Proceedings 1630, 134 (2014)M. Circella for the NEMO collaboration, Time calibration of the NEutrino Mediterranean Observatory (NEMO). Nucl. Instr. Methods A 602, 187 (2009)S. Aiello et al., Measurement of the atmospheric muon depth intensity relation with the NEMO phase-2 tower. Astropart. Phys. 66, 1 (2015)C. Hugon for the ANTARES and KM3NeT collaborations, Step by step simulation of phototubes for the KM3NeT and ANTARES optical modules. Nucl. Instr. Methods A 787, 189 (2015)Ch. Tamburini et al., Deep-sea bioluminescence blooms after dense water formation at the ocean surface. PLOS One 8, e67523 (2013