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The multiexciton quintet state, ⁵ TT, generated as a singlet fission intermediate in pairs of molecular chromophores, is a promising candidate as a qubit or qudit in future quantum information science schemes.

Here, e report the growth and characterization of MnPd₅P, a rare-earth-free ferromagnet, with T_C ≈ 295 K and planar anisotropy, and conduct a substitutional study with its antiferromagnetic analogue MnPt₅P. We provide a solution route to grow large single crystals of MnPd₅P and the series Mn(Pt_1–xPd_x)₅P by adding Mn into Pd-P and (Pt_1–xPd_x)-P based melts. All compounds in the family adopt the layered anti-CeCoIn5 type structure with the space group P4/mmm, and EDS and X-ray diffraction results indicate that MnPt₅P and MnPd₅P form a complete solid solution. Based on measurements of the temperature- and field-dependent magnetization and resistance, we constructmore » a temperature-composition (T-x) phase diagram for Mn(Pt_1–xPd_x)₅P and demonstrate that the initial antiferromagnetic order found in MnPt₅P is extraordinarily sensitive to Pd substitution. At low Pd fractions (x < 0.010), the single antiferromagnetic transition in pure MnPt₅P splits into a higher temperature ferromagnetic transition followed first, upon cooling, by a lower temperature ferromagnetic to antiferromagnetic transition and then by a re-entrant antiferromagnetic to ferromagnetic transition at even lower temperatures. The antiferromagnetic region makes up a bubble phase that persists up to x ≈ 0.008-0.009 for T ≈ 150 K, with all samples x < 0.008 recovering their initial ferromagnetic state upon further cooling to base temperature. Over the same low substitution range we find a non-monotonic change in the room temperature value of the unit cell volume, further suggesting that pure MnPt₅P is very close to an instability. Once x > 0.010, Mn(Pt_1–xPd_x)₅P undergoes a only single transition into the ferromagnetic phase. The Curie temperature initially increases rapidly with x, rising from T_C ≈ 197 K at x = 0.013 to a maximum of T_C ≈ 312 K for x ≈ 0.62, and then falling back to T_C ≈ 295 K for pure MnPd₅P (x = 1.00). Given that Pt and Pd are isoelectronic, this work raises questions as to the origin of the extreme sensitivity of the magnetic ground state in MnPt₅P upon introducing Pd.« less

In this work, we present the growth and basic magnetic and transport properties of Cr_1+xPt_5-xP. We show that single crystals can readily be grown from a high-temperature solution created by adding dilute quantities of Cr to Pt-P based melts. Like other 1-5-1 compounds, Cr_1+xPt_5-xP adopts a tetragonal P4/mmm, structure composed facesharing CrPts like slabs that are broken up along the c-axis by sheets of P atoms. EDS and X-ray diffraction measurements both suggest Cr_1+xPt_5-xP has mixed occupancy between Cr and Pt atoms, similar to what is found in the closely related compound CrPtg, giving real compositions of Cr_1.5Pt_4.5P (x =more » 0.5). We report that Cr_1.5Pt_4.5P orders ferromagnetically at T_c = 464.5 K with a saturated moment of ≈ 2.1 μs/Cr at 1.8 K. Likely owing to the strong spin-orbit coupling associated with the large quantity of high Z, Pt atoms, Cr_1.5Pt_4.5P has exceptionally strong planar anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and 300 K respectively. The resistance of Cr_1.5Pt_4.5P has a metallic temperature dependence with relatively weak magnetoresistance. Electronic band structure calculations show that CrPt₅P has a large peak in the density of states near the Fermi level which is split into spin majority and minority bands in the ferromagnetic state. Furthermore, the calculations suggest substantial hybridization between Cr-3d and Pt-5d states near the Fermi level, in agreement with the experimentally measured anisotropy.« less

Derived from the lateral fusion of benzene rings, acenes are a class of π-conjugated molecules containing a single aromatic sextet, where system size is inversely correlated with chemical stability. In the pursuit of creating graphene nanoribbons/nanowires, several extended-ring structures have been synthesized through linear combinations of azaacenes and pyrene. Importantly, these extended systems demonstrate enhanced chemical stability and allow for the construction of macromolecular-sized structures. In this report we present a combined quantum-chemical and experimental study to reveal the cost of these improved characteristics in fully carbon-based systems. The results clearly show that pyrene moieties inserted among acene units domore » not result in long acene-like structures, rather the pyrene-inserted acene is, electronically, a series of (nearly) isolated acenes. The origin of pyrene's electronic blocking effect and implications on oxidized and photoexcited states of these extended-ring systems are detailed. The results of this investigation definitively show that coupling pyrene in an orthogonal orientation (through the 4, 5/9, 10 positions or e/l faces) to acenes should be eschewed if nanographene-/nanowire-like structures are desired.« less