Spin Freezing and Its Impact on Pore Size, Tortuosity and Solid State

Spin freeze-drying, as a part of a continuous freeze-drying technology, is associated with a much higher drying rate and a higher level of process control in comparison with batch freeze-drying. However, the impact of the spin freezing rate on the dried product layer characteristics is not well understood at present. This research focuses on the relation between spin-freezing and pore size, pore shape, dried product mass transfer resistance and solid state of the dried product layer. This was thoroughly investigated via high-resolution X-ray micro-computed tomography (µCT), scanning electron microscopy (SEM), thermal imaging and solid state X-ray diffraction (XRD). It was concluded that slow spin-freezing rates resulted in the formation of highly tortuous structures with a high dried-product mass-transfer resistance, while fast spin-freezing rates resulted in lamellar structures with a low tortuosity and low dried-product mass-transfer resistance.

Development and Application of a Mechanistic Cooling and Freezing Model of the Spin Freezing Step within the Framework of Continuous Freeze-Drying

During the spin freezing step of a recently developed continuous spin freeze-drying technology, glass vials are rapidly spun along their longitudinal axis. The aqueous drug formulation subsequently spreads over the inner vial wall, while a cold gas flow is used for cooling and freezing the product. In this work, a mechanistic model was developed describing the energy transfer during each phase of spin freezing in order to predict the vial and product temperature change over time. The uncertainty in the model input parameters was included via uncertainty analysis, while global sensitivity analysis was used to assign the uncertainty in the model output to the different sources of uncertainty in the model input. The model was verified, and the prediction interval corresponded to the vial temperature profiles obtained from experimental data, within the limits of the uncertainty interval. The uncertainty in the model prediction was mainly explained (>96% of uncertainty) by the uncertainty in the heat transfer coefficient, the gas temperature measurement, and the equilibrium temperature. The developed model was also applied in order to set and control a desired vial temperature profile during spin freezing. Applying this model in-line to a continuous freeze-drying process may alleviate some of the disadvantages related to batch freeze-drying, where control over the freezing step is generally poor.

Evolution of spin freezing transition and structural, magnetic phase diagram of Dy$$_{2-\textit{x}}$$La$$_\textit{x}$$Zr$$_{2}$$O$$_{7}$$ (0 $$\le$$ $$\textit{x}$$ $$\le$$ 2.0)

Dy$$_{2}$$ 2 Zr$$_{2}$$ 2 O$$_{7}$$ 7 a disordered pyrochlore system, exhibits the spin freezing behavior under the application of the magnetic field. We have performed detailed magnetic studies of Dy$$_{2-\textit{x}}$$ 2 - x La$$_\textit{x}$$ x Zr$$_{2}$$ 2 O$$_{7}$$ 7 to understand the evolution of the magnetic spin freezing in the system. Our studies suggest the stabilization of the pyrochlore phase with the substitution of non-magnetic La along with the biphasic mixture of fluorite and pyrochlore phases for the intermediate compositions. We observed that the spin freezing (T$$_{f}$$ f $$\sim$$ ∼ 17 K) at higher La compositions (1.5 $$\le$$ ≤ $$\textit{x}$$ x $$\le$$ ≤ 1.99) is similar to the field-induced spin freezing for low La compositions (0 $$\le$$ ≤ $$\textit{x}$$ x $$\le$$ ≤ 0.5) and the well-known spin ice systems Dy$$_{2}$$ 2 Ti$$_{2}$$ 2 O$$_{7}$$ 7 and Ho$$_{2}$$ 2 Ti$$_{2}$$ 2 O$$_{7}$$ 7 . The low-temperature magnetic state for higher La compositions (1.5 $$\le$$ ≤ $$\textit{x}$$ x $$\le$$ ≤ 1.99) culminates into a spin-glass like state below 6 K. Cole–Cole plot and Casimir-du Pr$$\acute{e}$$ e ´ fit shows the narrow distribution of spin relaxation time in these compounds.

Exchange Bias in a Layered Metal–Organic Topological Spin Glass

<p><b>The discovery of conductive and magnetic two-dimensional (2D) materials is critical for the development of next generation spintronics devices. Coordination chemistry in particular represents a highly versatile, though underutilized, route toward the synthesis of such materials with designer lattices. Here, we report the synthesis of a conductive, layered 2D metal–organic kagome lattice, Mn₃(C₆S₆), using mild solution-phase chemistry. Strong geometric<i> </i>spin frustration in this system mediates spin freezing at low temperatures, which results in glassy magnetic behavior consistent with a geometrically frustrated (topological) spin glass. Notably, the material exhibits a large exchange bias of 1625 Oe, providing the first example of exchange bias in a coordination solid or a topological spin glass. More generally, these results demonstrate the potential utility of geometrically frustrated lattices in the design of new nanoscale spintronic materials.</b></p>

Exchange Bias in a Layered Metal–Organic Topological Spin Glass

<p><b>The discovery of conductive and magnetic two-dimensional (2D) materials is critical for the development of next generation spintronics devices. Coordination chemistry in particular represents a highly versatile, though underutilized, route toward the synthesis of such materials with designer lattices. Here, we report the synthesis of a conductive, layered 2D metal–organic kagome lattice, Mn₃(C₆S₆), using mild solution-phase chemistry. Strong geometric<i> </i>spin frustration in this system mediates spin freezing at low temperatures, which results in glassy magnetic behavior consistent with a geometrically frustrated (topological) spin glass. Notably, the material exhibits a large exchange bias of 1625 Oe, providing the first example of exchange bias in a coordination solid or a topological spin glass. More generally, these results demonstrate the potential utility of geometrically frustrated lattices in the design of new nanoscale spintronic materials.</b></p>

Role of spin-glass behavior in the formation of exotic magnetic states in GdB6

Randomness and frustration are believed to be two crucial criteria for the formation of spin glass state. However, the spin freezing occurs in some well-ordered crystals below the related temperature Tf due to the instability of each spin state, which induces the variation of either magnetic moment value or exchange energy. Here we explore the new mechanism of the in-site originated disorder in antiferromagnets Gd0.73La0.27B6 and GdB6, which is caused by the random mutual shifts of Gd3+ spins from the centrally symmetrical positions in the regular cubic lattice. The universal scaling of ESR linewidth temperature dependencies to the power law ΔH(T) ~ ((T − TD)/TD)α with α = − 1.1 ± 0.05 in the paramagnetic phase of both compounds demonstrates the identity of the origin of magnetic randomness. In Gd0.73La0.27B6 the resulting random spin configurations freeze at Tf ≈ 10.5 K where the maximum of magnetization is observed. Below Tf the splitting of ZFC and FC magnetization curves takes place as well as the magnetic state depends on the antecedent sample history. In the case of GdB6 the coherent displacement of Gd ions compete with these random shifts forming an antiferromagnetic (AFM) phase at TN = 15.5 K, which prevails over the spin freezing at Tf ≈ 13 K, expected from the ESR data. The observation of the hysteresis of the ESR spectrum in the AFM phase suggests that its properties may be determined by the competition of two types of AFM orders, which results in formation of stable magnetic domains with nonequivalent positions of AFM Gd pairs at T < 10 K.