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- ItemPhase transition and anomalous low temperature ferromagnetic phase in Pr 0.6Sr 0.4MnO 3 single crystals(New York, NY : Springer Science + Business Media B.V., 2009) Rößler, S.; Harikrishnan, S.; Naveen Kumar, C.M.; Bhat, H.L.; Elizabeth, S.; Rößler, U.K.; Steglich, F.; Wirth, S.We report on the magnetic and electrical properties of Pr 0.6Sr 0.4MnO 3 single crystals. This compound undergoes a continuous paramagnetic-ferromagnetic transition with a Curie temperature T C301 K and a first-order structural transition at T S64 K. At T S, the magnetic susceptibility exhibits an abrupt jump, and a corresponding small hump is seen in the resistivity. The critical behavior of the static magnetization and the temperature dependence of the resistivity are consistent with the behavior expected for a nearly isotropic ferromagnet with short-range exchange belonging to the Heisenberg universality class. The magnetization (M-H) curves below T S are anomalous in that the virgin curve lies outside the subsequent M-H loops. The hysteretic structural transition at T S as well as the irreversible magnetization processes below T S can be explained by phase separation between a high-temperature orthorhombic and a low-temperature monoclinic ferromagnetic phase.
- ItemFerroelectric switching in epitaxial GeTe films(New York : American Institute of Physics, 2014) Kolobov, A.V.; Kim, D.J.; Giussani, A.; Fons, P.; Tominaga, J.; Calarco, R.; Gruverman, A.In this paper, using a resonance-enhanced piezoresponse force microscopy approach supported by density functional theory computer simulations, we have demonstrated the ferroelectric switching in epitaxial GeTe films. It has been shown that in films with thickness on the order of several nanometers reversible reorientation of polarization occurs due to swapping of the shorter and longer Ge-Te bonds in the interior of the material. It is also hinted that for ultra thin films consisting of just several atomic layers weakly bonded to the substrate, ferroelectric switching may proceed through exchange of Ge and Te planes within individual GeTe layers.
- ItemThe impact of surface morphology on the magnetovolume transition in magnetocaloric LaFe11.8Si1.2(New York : American Institute of Physics, 2016) Waske, A.; Lovell, E.; Funk, A.; Sellschopp, K.; Rack, A.; Giebeler, L.; Gostin, P.F.; Fähler, S.; Cohen, L.F.First order magnetocaloric materials reach high entropy changes but at the same time exhibit hysteresis losses which depend on the sample’s microstructure. We use non-destructive 3D X-ray microtomography to understand the role of surface morphology for the magnetovolume transition of LaFe11.8Si1.2. The technique provides unique information on the spatial distribution of the volume change at the transition and its relationship with the surface morphology. Complementary Hall probe imaging confirms that on a morphologically complex surface minimization of strain energy dominates. Our findings sketch the way for a tailored surface morphology with low hysteresis without changing the underlying phase transition.
- ItemAll-on-Chip Concurrent Measurements of the Static Magnetization and of the Electron Spin Resonance with Microcantilevers(Wien [u.a.] : Springer, 2021) Alfonsov, A.; Büchner, B.; Kataev, V.A large variety of the samples of novel magnetic materials, which are of high interest due to their exotic properties, are only available in very small sizes. In some cases, it is not possible to synthesize large single crystals; in other cases, the small size itself is the key prerequisite to manifest a specifically interesting property of the material. The smallness of a sample rises a problem of the detection of the static magnetic response and of the electron spin resonance (ESR) signal. To overcome this problem, we propose to use a cantilever-based (torque-detected) setup with the capability of a simultaneous measurement of ESR and static magnetization. This setup offers a high sensitivity and the ability to acquire along with the ESR signal the components of the magnetization tensor in a single experimental run. Here, we present the working principle of this setup, as well as the estimate of its sensitivity from the measurements on the standard Co Tutton salt sample. © 2021, The Author(s).
- ItemMagnetic field-induced twin boundary motion in polycrystalline Ni-Mn-Ga fibres(Milton Park : Taylor & Francis, 2008) Scheerbaum, N.; Heczko, O.; Liu, J.; Hinz, D.; Schultz, L.; Gutfleisch, O.Magnetic field-induced twin boundary motion leading to large magnetic field-induced strain of ~1.0% was established in polycrystalline Ni50.9Mn27.1Ga22.0 (at.%) fibres at room temperature (~60–100 μm in diameter and ~3 mm in length). The fibres' grains are as large as the fibre diameter and of random orientation. At room temperature, a ferromagnetic 5M martensite is found. Magnetic field-induced twin boundary motion was indicated by magnetic measurements and validated by electron backscatter diffraction (EBSD). The application of a magnetic field shifts the equilibrium temperature of martensite and austenite by ~0.4 K T−1, which agrees with calculations using the Clapeyron–Clausius approach.
- ItemHyper-domains in exchange bias micro-stripe pattern(Milton Park : Taylor & Francis, 2008) Theis-Bröhl, K.; Westphalen, A.; Zabel, H.; Rücker, U.; McCord, J.; Höink, V.; Schmalhorst, J.; Reiss, G.; Weis, T.; Engel, D.; Ehresmann, A.; Toperverg, B.P.A combination of experimental techniques, e.g. vector-MOKE magnetometry, Kerr microscopy and polarized neutron reflectometry, was applied to study the field induced evolution of the magnetization distribution over a periodic pattern of alternating exchange bias (EB) stripes. The lateral structure is imprinted into a continuous ferromagnetic/antiferromagnetic EB bilayer via laterally selective exposure to He-ion irradiation in an applied field. This creates an alternating frozen-in interfacial EB field competing with the external field in the course of the re-magnetization. It was found that in a magnetic field applied at an angle with respect to the EB axis parallel to the stripes the re-magnetization process proceeds via a variety of different stages. They include coherent rotation of magnetization towards the EB axis, precipitation of small random (ripple) domains, formation of a stripe-like alternation of the magnetization, and development of a state in which the magnetization forms large hyper-domains comprising a number of stripes. Each of those magnetic states is quantitatively characterized via the comprehensive analysis of data on specular and off-specular polarized neutron reflectivity. The results are discussed within a phenomenological model containing a few parameters, which can readily be controlled by designing systems with a desired configuration of magnetic moments of micro- and nano-elements.
- ItemDiode-pumped continuous-wave laser operation of co-doped (Ho,Tm):KLu(WO4)2 monoclinic crystal(Amsterdam [u.a.] : Elsevier, 2013) Jambunathan, V.; Mateos, X.; Cinta Pujol, M.; Josep Carvajal, J.; Griebner, U.; Petrov, V.; Aguiló, M.; Díaz, F.We report on room-temperature continuous-wave laser operation at 2.06 μm in co-doped (0.5 at% Ho, 5.0 at% Tm):KLu(WO4)2 monoclinic crystal pumped at 805 nm by a commercially available AlGaAs diode laser stack. A maximum output power of 93 mW and a slope efficiency of 14.7% with respect to absorbed power were achieved.
- ItemRolled-up magnetic microdrillers: Towards remotely controlled minimally invasive surgery(Cambridge [u.a.] : Royal Society of Chemistry, 2013) Xi, W.; Solovev, A.A.; Ananth, A.N.; Gracias, D.H.; Sanchez, S.; Schmidt, O.G.Self-folded magnetic microtools with sharp ends are directed at enabling drilling and related incision operations of tissues, ex vivo, in a fluid with a viscosity similar to that of blood. These microtools change their rotation from a horizontal to a vertical one when they are immersed into a rotational magnetic field. Novel self-assembly paradigms with magnetic materials can enable the creation of remotely controlled and mass-produced tools for potential applications in minimally invasive surgery.
- ItemMagnetocaloric performance of the three-component Ho1-xErxNi2 (x = 0.25, 0.5, 0.75) Laves phases as composite refrigerants([London] : Macmillan Publishers Limited, part of Springer Nature, 2022) Ćwik, Jacek; Koshkid’ko, Yurii; Nenkov, Konstantin; Tereshina-Chitrova, Evgenia; Małecka, Małgorzata; Weise, Bruno; Kowalska; KarolinaTo date, significant efforts have been put into searching for materials with advanced magnetocaloric properties which show promise as refrigerants and permit realization of efficient cooling. The present study, by an example of Ho1−xErxNi2, develops the concept of magnetocaloric efficiency in the rare-earth Laves-phase compounds. Based on the magneto-thermodynamic properties, their potentiality as components of magnetocaloric composites is illustrated. The determined regularities in the behaviour of the heat capacity, magnetic entropy change, and adiabatic temperature change of the system substantiate reaching high magnetocaloric potentials in a desired temperature range. For the Ho1−xErxNi2 solid solutions, we simulate optimal molar ratios and construct the composites used in magnetic refrigerators performing an Ericsson cycle at low temperatures. The tailored magnetocaloric characteristics are designed and efficient procedures for their manufacturing are developed. Our calculations based on the real empirical data are very promising and open avenue to further experimental studies. Systems showing large magnetocaloric effect (MCE) at low temperatures are of importance due to their potential utilization in refrigeration for gas liquefaction.
- ItemSpin-orbit coupling control of anisotropy, ground state and frustration in 5d2 Sr2MgOsO6(London : Nature Publishing Group, 2016) Morrow, Ryan; Taylor, Alice E.; Singh, D.J.; Xiong, Jie; Rodan, Steven; Wolter, A.U.B.; Wurmehl, Sabine; Büchner, Bernd; Stone, M.B.; Kolesnikov, A.I.; Aczel, Adam A.; Christianson, A.D.; Woodward, Patrick M.The influence of spin-orbit coupling (SOC) on the physical properties of the 5d2 system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d2 system of 0.60(2) μB –a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d2 systems relative to their 5d3 counterparts, providing an explanation of the high TN found in Sr2MgOsO6.