2023, Sahoo, M., Salman, Z., Allodi, G., Isaeva, A., Folkers, L., Wolter, A.U.B., Büchner, B., De Renzi, R.

We investigated the magnetic properties of polycrystalline samples of the intrinsic magnetic topological insulators MnPn2Te4, with pnictogen Pn = Sb, Bi, by bulk magnetization and μSR. DC susceptibility detects the onset of magnetic ordering at TN = 27 K and 24 K and a field dependence of the macroscopic magnetization compatible with ferri- (or ferro-) and atiferro- magnetic ordering, respectively. Weak transverse field (wTF) Muon Spin Rotation (μSR) confirms the homogeneous bulk nature of magnetic ordering at the same two distinct transition temperatures. Zero Field (ZF) μSR shows that the Sb based material displays a broader distribution of internal field at the muon, in accordance with a larger deviation from the stoichiomectric composition and a higher degree of positional disorder (Mn at the Pn(6c) site), which however does not affect significantly the sharpness of the thermodynamic transition, as detected by the muon magnetic volume fraction and the observability of a critical divergence in the longitudinal and transverse muon relaxation rates.

2021, Ćwik, J., Koshkid’ko, Yu, Nenkov, K., Kolchugina, N.

Heat capacity measurements have been performed for multicomponent (Ho0.9Er0.1)1-xGdxCo2 compounds with x = 0.05, 0.1, and 0.15. The isothermal magnetic entropy change, ΔSmag, allowing the estimation of the magnetocaloric effect, was determined based on the heat capacity measurements in magnetic fields up to 2 T. A numerical method, with the magnetic entropy change of individual (Ho0.9Er0.1)1-xGdxCo2 compounds, was used to calculate the optimal molar composition of the constituents and the resulting change of the isothermal magnetic entropy of composite, ΔScomp. The results show that proposed composite can be considered as a refrigerant material in magnetic refrigerators performing an Ericsson cycle in a temperature range of 90-130 K.

2021, Kulbakov, Anton A., Avdoshenko, Stanislav M., Puente-Orench, Inés, Deeb, Mahmoud, Doerr, Mathias, Schlender, Philipp, Doert, Thomas, Inosov, Dmytro S.

Yb- and Ce-based delafossites were recently identified as effective spin-1/2 antiferromagnets on the triangular lattice. Several Yb-based systems, such as NaYbO2, NaYbS2, and NaYbSe2, exhibit no long-range order down to the lowest measured temperatures and therefore serve as putative candidates for the realization of a quantum spin liquid. However, their isostructural Ce-based counterpart KCeS2 exhibits magnetic order below TN = 400 mK, which was so far identified only in thermodynamic measurements. Here we reveal the magnetic structure of this long-range ordered phase using magnetic neutron diffraction. We show that it represents the so-called 'stripe-yz' type of antiferromagnetic order with spins lying approximately in the triangular-lattice planes orthogonal to the nearest-neighbor Ce–Ce bonds. No structural lattice distortions are revealed below TN, indicating that the triangular lattice of Ce3+ ions remains geometrically perfect down to the lowest temperatures. We propose an effective Hamiltonian for KCeS2, based on a fit to the results of ab initio calculations, and demonstrate that its magnetic ground state matches the experimental spin structure.

2021, Oka, T., Yamanaka, K., Sudo, K., Dadiel, L., Ogawa, J., Yokoyama, K., Häßler, W., Noudem, J., Berger, K., Sakai, N., Miryala, M., Murakami, M.

MgB2 superconducting bulk materials are characterized as simple and uniform metallic compounds, and capable of trapping field of non-distorted conical shapes. Although pulsed-field magnetization technique (PFM) is expected to be a cheap and an easy way to activate them, the heat generation due to the magnetic flux motion causes serious degradation of captured fields. The authors precisely estimated the flux trapping property of the bulk samples, found that the flux-shielding effect closely attributed to the sample dimensions. The magnetic field capturing of Ti-5.0wt% sample reached the highest value of 0.76 T. The applied field which reached the centre of the sample surface shifted from 1.0 T to 1.2 T with increasing sample thickness from 3.67 mm to 5.80 mm. This means that the shielding effect was enhanced with increasing the sample thickness. Moreover, Ti-addition affected the frequency of flux jump happenings. The occurrence of flux jumps was suppressed in 5.0wt%Ti-added sample. This means that the heat capacity of the compounds was promoted by Ti addition.

2022, Schuster, A.K., Voigt, K., Klemmed, B., Hartley, N.J., Lütgert, J., Zhang, M., Bähtz, C., Benad, A., Brabetz, C., Cowan, T., Döppner, T., Erb, D.J., Eychmüller, A., Facsko, S., Falcone, R.W., Fletcher, L.B., Frydrych, S., Ganzenmüller, G.C., Gericke, D.O., Glenzer, S.H., Grenzer, J., Helbig, U., Hiermaier, S., Hübner, R., Laso Garcia, A., Lee, H.J., MacDonald, M.J., McBride, E.E., Neumayer, P., Pak, A., Pelka, A., Prencipe, I., Prosvetov, A., Rack, A., Ravasio, A., Redmer, R., Reemts, D., Rödel, M., Schoelmerich, M., Schumacher, D., Tomut, M., Turner, S.J., Saunders, A.M., Sun, P., Vorberger, J., Zettl, A., Kraus, D.

This work presents first insights into the dynamics of free-surface release clouds from dynamically compressed polystyrene and pyrolytic graphite at pressures up to 200 GPa, where they transform into diamond or lonsdaleite, respectively. These ejecta clouds are released into either vacuum or various types of catcher systems, and are monitored with high-speed recordings (frame rates up to 10 MHz). Molecular dynamics simulations are used to give insights to the rate of diamond preservation throughout the free expansion and the catcher impact process, highlighting the challenges of diamond retrieval. Raman spectroscopy data show graphitic signatures on a catcher plate confirming that the shock-compressed PS is transformed. First electron microscopy analyses of solid catcher plates yield an outstanding number of different spherical-like objects in the size range between ten(s) up to hundreds of nanometres, which are one type of two potential diamond candidates identified. The origin of some objects can unambiguously be assigned, while the history of others remains speculative.

2022, Zaiets, Oleksandr, Kravchuk, Volodymyr P., Pylypovskyi, Oleksandr V., Makarov, Denys, Sheka, Denis D.

Vertically stacked exchange coupled magnetic heterostructures of cylindrical geometry can host complex noncolinear magnetization patterns. By tuning the interlayer exchange coupling between a layer accommodating magnetic vortex state and an out-of-plane magnetized layer, one can efficiently realize new topological chiral textures such as cone state vortices and circular stripe domains. We study how the number of circular stripes can be controlled by both the interlayer exchange coupling and the sample geometrical parameters. By varying geometrical parameters, a continuous phase transition between the homogeneous state, cone state vortex, circular stripe domains, and the imprinted vortex takes place, which is analysed by full scale micromagnetic simulations. The analytical description provides an intuitive pictures of the magnetization textures in each of these phases. The possibility to realize switching between different states allows for engineering magnetic textures with possible applications in spintronic devices.