The Berry Group has synthesized an unusual heterotrimetallic MoMo-Ni chain complex for which the following effect is observed: ferromagnetic alignment of δ-symmetry electrons at both the Mo2 and Ni centers arising from delocalization of a σ-symmetry electron across the MoMo-Ni chain .[1]

Heterometallic chain compounds Mo2Ni(dpa)4Cl2 (compound 1) and [Mo2Ni(dpa)4Cl2]OTf  (dpa = 2,2’-dipyridylamine) (compound 2) were prepared and studied with SQUID magnetometry.

Crystal structures of compound 1 (left) and 2 (right.) Hydrogen atoms and any solvent molecules have been removed for clarity.

Magnetic susceptibility data for compound 1 and 2 are shown in the figure below. The χT value for 1 at 300 K, 1.09 emu*K*mol-1, agrees with the spin-only value for an S=1 system of 1.0 emu*K*mol-1. In the case of 2 the high temperature limit in our data is 1.75 emu*K*mol-1, for which the only reasonable assignment is to an S=3/2 system (spin only value of 1.875 emu*K*mol-1). Thus, the data for 1 and 2 were modeled as S=1 or S=3/2 systems, respectively. For both 1 and 2, a sharp downward feature is seen in the χT versus T plot below 50 K, indicative of zero field splitting. The data for 1 and 2 were fitted with giso= 2.053(3); |D| =9.19(3) cm-1, and giso=1.916(3); |D| = 2.86(4) cm-1, respectively.

Variable temperature magnetic susceptibility data for compound 1 (black squares) and 2 (red triangles).

Thus, in reporting the first example of a one-electron oxidized Mo2MB(dpa)4Cl2 monocation in which MB represents a first-row transition metal, they find that the cation displays unusual, strongly ferromagnetic coupling affording an S=3/2 ground state that persists to room temperature. This conclusion is supported through EPR spectroscopy, SQUID magnetometry, as well as DFT computations. The ferromagnetism arises via a new mechanism in which a delocalized itinerant electron couples ferromagnetically to electrons in orthogonal orbitals in neighboring spin centers. The resulting magnitude of the coupling (J≥150 cm-1) suggests promise for the use of this effect in the design of novel magnetic materials.


Jin Group reported a method for the low pressure, low temperature synthesis of both FeGe and Fe1−xCoxGe alloys with the cubic B20 structure. AC magnetic susceptibility analysis of Fe0.95Co0.05Ge provided clear evidence for the existence of a skyrmion phase observed in any Fe1−xCoxGe alloy compound for the first time. These results not only introduce a more facile synthetic method to make high quality cubic B20 FeGe and Fe1−xCoxGe materials without the need for a high pressure apparatus but also enable the construction of Fe0.95Co0.05Ge’s magnetic phase diagram. [2]

Magnetic property analysis and magnetic phase determination of Fe0.95Co0.05Ge. (a) DC and (b) AC magnetic field sweeps of Fe0.95Co0.05Ge. Transitions in the (b) AC field sweeps are characteristic of a skyrmion phase, and the relevant magnetic transitions have been highlighted with dashed lines. (c, d) Magnetic phase diagrams for (c) Fe0.95Co0.05Ge and (d) FeGe illustrating the pocket of stability for the skyrmion phase as well as the existence of the other relevant magnetic phases: helimagnetic, conical, field polarized, and paramagnetic (above Tc).




[1] Chipman, Jill A., and John F. Berry. “Extraordinarily Large Ferromagnetic Coupling (J≥ 150 cm− 1) by Electron Delocalization in a Heterometallic Mo≣ Mo− Ni Chain Complex.” Chemistry-A European Journal 24.7 (2018): 1494-1499.

[2] Stolt, Matthew J., et al. “Chemical Pressure Stabilization of the Cubic B20 Structure in Skyrmion Hosting Fe1-xCoxGe Alloys.”Chemistry of Materials (2018): 1146-1154.