We study random dense packings of Heisenberg dipoles by numerical simulation. The dipoles are at the centers of identical spheres that occupy fixed random positions in space and fill a fraction $\mathrm{\Phi }$ of the spatial volume. The parameter $\mathrm{\Phi }$ ranges from rather low values, typical of amorphous ensembles, to the maximum $\mathrm{\Phi }=0.64$ that occurs in the random-close-packed limit. We assume that the dipoles can freely rotate and have no local anisotropies. As well as the usual thermodynamical variables, the physics of such systems depends on $\mathrm{\Phi }$. Concretely, we explore the magnetic ordering of these systems in order to depict the phase diagram in the temperature-$\mathrm{\Phi }$ plane. For $\mathrm{\Phi }\gtrsim 0.49$ we find quasi-long-range ferromagnetic order coexisting with strong long-range spin-glass order. For $\mathrm{\Phi }\lesssim 0.49$ the ferromagnetic order disappears giving way to a spin-glass phase similar to the ones found for Ising dipolar systems with strong frozen disorder.

• Received 22 July 2020
• Revised 29 October 2020
• Accepted 5 November 2020

DOI:https://doi.org/10.1103/PhysRevB.102.184423