The vortex phase diagram in ${\mathrm{HgBa}}_2{\mathrm{CuO}}_{4+\delta }$ single crystals ${(T}_c=95\mathrm{}$ K) is investigated using dc-magnetic measurements. The irreversibility magnetic field $H_{\mathrm{irr}}\mathrm{}\left(T\right)\mathrm{}$ decreases exponentially in the temperature range $20<~T<~88$ K. At $T^{*}\approx 88$ K, the $H_{\mathrm{irr}}\mathrm{}\left(T\right)\mathrm{}$ curve changes slope abruptly and a new mechanism controls the irreversibility up to $T_c.$ Magnetization versus magnetic field measurements $\left(\mathbf{H}\Vert c\right)$ show a second peak (increase of the critical current) in the range $5<~T<~50$ K. The overall picture resembles the phase diagram of the ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ and ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ compounds if one considers the anisotropy $\varepsilon {=(m/M)\mathrm{}}^{1/2}$ of ${\mathrm{HgBa}}_2{\mathrm{CuO}}_{4+\delta },$ which lies in between the two others.

We have studied the vortex matter phase diagram in two carbon doped ${\mathrm{MgB}}_{2-x}{\mathrm{C}}_x$ ($x=0.04$ and 0.1) single crystals. We have found that, as in pristine ${\mathrm{MgB}}_2$, the peak effect is also present in carbon doped crystals. The regime where the peak effect is developed is more extended in comparison to the undoped crystal. The enhancement of the peak effect regime, combined with the higher $H_{c2}^c\left(0\right)$, makes doped ${\mathrm{MgB}}_2$ more favorable for practical applications. The absence of significant bulk pinning below the line $H_{\mathrm{on}}\left(T\right)$, which denotes the onset points of the peak effect, implies that the Bragg glass phase is present for $H<H_{\mathrm{on}}\left(T\right)$. Interestingly the end points $H_{\mathrm{ep}}\left(T\right)$ of the peak effect are placed well below the upper critical fields $H_{c2}\left(T\right)$. The unexpected absence of bulk pinning above the end-point line $H_{\mathrm{ep}}\left(T\right)$ of the peak effect implies the presence of a slightly pinned vortex phase in the regime $H_{\mathrm{ep}}\left(T\right)<H<H_{c2}\left(T\right)$.

The temperature and magnetic-field dependence of activation energy $U_{\mathrm{o}}\mathrm{}(T,H)\mathrm{}$ for creep has been studied in an $\mathrm{Hg}{\mathrm{Ba}}_2{\mathrm{CuO}}_{4+\delta }$ single crystal below and above the “fishtail” peak $H_{\mathrm{sp}}\mathrm{}\left(T\right).$ At constant temperature, $U_{\mathrm{o}}\mathrm{}\left(H\right)\mathrm{}$ increases up to $H_{\mathrm{sp}}^{/}\mathrm{}\left(T\right)\mathrm{}$ and then for $H>\mathrm{}{H}_{\mathrm{sp}}^{/}\mathrm{}\left(T\right)\mathrm{}$ it decreases. $H_{\mathrm{sp}}^{/}\mathrm{}\left(T\right)\mathrm{}$ is located lower than the field $H_{\mathrm{sp}}\mathrm{}\left(T\right)\mathrm{}$ deduced from the hysteresis loops. The decrease of the activation energy is probably indicative of a plastic-type creep of the vortex lattice. We demonstrate that the overall behavior of $U_{\mathrm{o}}\mathrm{}(T,H)\mathrm{}$ at the second magnetization peak line $H_{\mathrm{sp}}\mathrm{}\left(T\right)\mathrm{}$ in the phase diagram of $\mathrm{Hg}{\mathrm{Ba}}_2{\mathrm{CuO}}_{4+\delta }$ exhibits similarities with that observed in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ and $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.95}$ compounds.

Two-dimensional (2D) metal borides are a class of ceramic materials with diverse structural and topological properties. These diverse material properties of metal borides are what forms the basis of their interdisciplinarity and their applicability in various research fields. In this study, we highlight which fundamental and practical parameters need to be taken into consideration when designing nanomaterials for specific applications. A simple one-pot chemical reduction method was applied for the synthesis of manganese mono-boride nanoflakes at room temperature. How the specific surface area and boron-content of the as-synthesized manganese mono-boride nanoflakes influence their magnetic and electrocatalytic properties is reported. The sample with the highest specific surface area and boron content demonstrated the best magnetic and electrocatalytic properties in the HER. Whereas the sample with the lowest specific surface area and boron content exhibited the best electric conductivity and electrocatalytic properties in the OER.

The reaction of the Schiff base ligand o-OH-C₆H₄-CH=N-C(CH₂OH)₃, H₄L, with Ni(O₂CMe)₂·4H₂O and lanthanide nitrate salts in a 4:2:1 ratio lead to the formation of the trinuclear complexes [Ni₂Ln(H₃L)₄(O₂CMe)₂](NO₃) (Ln = Sm (1), Eu (2), Gd (3), Tb (4)). The complex cations contain the strictly linear Ni^II-Ln^III-Ni^II moiety. The central Ln^III ion is bridged to each of the terminal Ni^II ions through two deprotonated phenolato groups from two different ligands. Each terminal Ni^II ion is bound to two ligands in distorted octahedral N₂O₄ environment. The central lanthanide ion is coordinated to four phenolato oxygen atoms from the four ligands, and four carboxylato oxygen atoms from two acetates which are bound in the bidentate chelate mode. The lattice structure of complex 4 consists of two interpenetrating, supramolecular diamond like lattices formed through hydrogen bonds among neighboring trinuclear clusters. The magnetic properties of 1–4 were studied. For 3 the best fit of the magnetic susceptibility and isothermal M(H) data gave J_NiGd = +0.42 cm⁻¹, D = +2.95 cm⁻¹ with g_Ni = g_Gd = 1.98. The ferromagnetic nature of the intramolecular Ni···Gd interaction revealed ground state of total spin S = 11/2. The magnetocaloric effect (MCE) parameters for 3 show that the change of the magnetic entropy (−ΔS_m) reaches a maximum of 14.2 J kg⁻¹ K⁻¹ at 2 K. A brief literature survey of complexes containing the Ni^II-Ln^III-Ni^II moiety is discussed in terms of their structural properties.

Fe₃O₄ nanoparticles “decorated” by LAPONITE® nanodisks have been materialized utilizing the Schikorr reaction and tested as mediators of heat for localized magnetic hyperthermia (MH) and as magnetic resonance imaging (MRI) agents.