Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias.

Rational material design can accelerate the discovery of materials with improved functionalities. This approach can be implemented in Heusler compounds with tunable magnetic sublattices to demonstrate unprecedented magnetic properties. Here, we have designed a family of Heusler alloys with a compensated ferrimagnetic state. In the vicinity of the compensation composition in Mn-Pt-Ga, a giant exchange bias (EB) of more than 3 T and a large coercivity are established. The large exchange anisotropy originates from the exchange interaction between the compensated host and ferrimagnetic clusters that arise from intrinsic anti-site disorder. Our design approach is also demonstrated on a second material with a magnetic transition above room temperature, Mn-Fe-Ga, exemplifying the universality of the concept and the feasibility of room-temperature applications. These findings may lead to the development of magneto-electronic devices and rare-earth-free exchange-biased hard magnets, where the second quadrant magnetization can be stabilized by the exchange bias.

A missing high-spin molecule in the family of cyanido-bridged heptanuclear heterometal complexes, [(LCu(II))6Fe(III)(CN)6]3+, and its Co(III) and Cr(III) analogues, accompanied in the crystal by a novel octameric water cluster.

Three isostructural cyanido-bridged heptanuclear complexes, [{Cu(II)(saldmen)(H2O)}6{M(III)(CN)6}]-(ClO4)3·8H2O (M= Fe(III) 2; Co(III), 3; Cr(III) 4), have been obtained by reacting the dinuclear copper(II) complex, [Cu2(saldmen)2(µ-H2O)(H2O)2](ClO4)2·2H2O 1, with K3[Co(CN)6], K4[Fe(CN)6], and K3[Cr(CN)6], respectively (Hsaldmen is the Schiff base resulting from the condensation of salicylaldehyde with N,N-dimethylethylenediamine). A unique octameric water cluster, with bicyclo[2,2,2]octane-like structure, is sandwiched between the heptanuclear cations in 2, 3 and 4. The cryomagnetic investigations of compounds 2 and 4 reveal ferromagnetic couplings of the central Fe(III) or Cr(III) ions with the Cu(II) ions (J(CuFe) = +0.87 cm⁻¹, J(CuCr) = +30.4 cm⁻¹). The intramolecular Cu···Cu exchange interaction in 3, across the diamagnetic cobalt(III) ion, is -0.3 cm⁻¹. The solid-state ¹H-NMR spectra of compounds 2 and 3 have been investigated.