Pulmonary metastasis of breast cancer cells is promoted by a distinct population of macrophages, metastasis-associated macrophages (MAMs), which originate from inflammatory monocytes (IMs) recruited by the CC-chemokine ligand 2 (CCL2). We demonstrate here that, through activation of the CCL2 receptor CCR2, the recruited MAMs secrete another chemokine ligand CCL3. Genetic deletion of CCL3 or its receptor CCR1 in macrophages reduces the number of lung metastasis foci, as well as the number of MAMs accumulated in tumor-challenged lung in mice. Adoptive transfer of WT IMs increases the reduced number of lung metastasis foci in Ccl3 deficient mice. Mechanistically, Ccr1 deficiency prevents MAM retention in the lung by reducing MAM-cancer cell interactions. These findings collectively indicate that the CCL2-triggered chemokine cascade in macrophages promotes metastatic seeding of breast cancer cells thereby amplifying the pathology already extant in the system. These data suggest that inhibition of CCR1, the distal part of this signaling relay, may have a therapeutic impact in metastatic disease with lower toxicity than blocking upstream targets.

Magnets with noncentrosymmetric lattice structures can host a three-dimensional noncoplanar spin texture called the magnetic hedgehog lattice (HL) with a periodic array of magnetic monopoles and anti-monopoles. Despite recent discovery of two types of short-period HLs in MnSi1−xGex, their microscopic origin remains elusive. Here, we study the stability of such magnetic HLs for an effective spin model with long-range interactions arising from the itinerant nature of electrons. By variational calculations and simulated annealing, we find that the HLs are stabilized in the ground state at zero magnetic field by the synergetic effect of the antisymmetric exchange interactions generated by the spin-orbit coupling and the multiple-spin interactions generated by the spin-charge coupling. We also clarify the full phase diagram in the magnetic field, which includes multiple phase transitions with changes in the number of monopoles and anti-monopoles.Chirality, often termed as handedness, is a key concept in a broad field of science, ranging from particle physics to biology. In condensed matter physics, chiral magnetic textures, which break both inversion and mirror symmetries in additon to time-reversal symmetry, have recently attracted considerable attention for potential applications to next-generation electronic devices. There are a variety of the chiral magnetic textures, such as skyrmion lattices [1] and chiral soliton lattices [2]. Noncollinear and noncoplanar spin arrangements in these textures generate emergent electromagnetic fields through the Berry phase mechanism, which induce unconventional transport, optical, and magnetoelectric properties [3][4][5].Recently, a three-dimensional chiral magnetic texture, which is called the hedgehog lattice (HL), was discovered in the B20-type compound MnGe [6,7]. The magnetic structure is characterized by cubic three wave vectors, and hence, it is referred as the triple-Q hedgehog lattice (3Q-HL) [ Fig. 1(a)]. The 3Q-HL has a periodic array of hyperbolic hedgehog and anti-hedgehog spin textures, which generates an emergent magnetic field with a periodic array of radial hedgehogs and anti-hedgehogs regarded as magnetic monopoles and anti-monopoles, as shown in Fig. 1(c) [8][9][10]. The peculiar magnetic field was discussed as a source of the enormous topological Hall effect [11] and thermoelectoric effect [12,13]. In addition, in MnSi 1−x Ge x , the 3Q-HL changes into a different HL characterized by tetrahedral four wave vectors, dubbed the quadruple-Q hedgehog lattice (4Q-HL) [ Fig. 1(b)] [14,15]. Remarkably, the magnetic periods of these 3Q-and 4Q-HLs are very short ∼ 2-3 nm, in contrast to most of the skyrmion lattices.Such magnetic HLs have been theoretically studied prior to the experimental discovery, e.g., by the Ginzburg-Landau theory [16], variational calculations [17], and Monte Carlo (MC) simulations [18]. The variational study for a classical spin model showed that the 3Q-HL is not stabilized, whereas the 4Q-HL is obtained in an applied magnetic field [17]. The 4Q...

Unbiased quantum Monte-Carlo simulations are performed on the nearest-neighbor spin-1 2 pyrochlore XXZ model with an antiferromagnetic longitudinal and a weak ferromagnetic transverse exchange couplings, J and J ⊥ . The specific heat exhibits a broad peak at TCSI ∼ 0.2J associated with a crossover to a classical Coulomb liquid regime showing a suppressed spin-ice monopole density, a broadened pinch-point singularity, and the Pauling entropy for |J ⊥ | J, as in classical spin ice. On further cooling, the entropy restarts decaying for J ⊥ > J ⊥c ∼ −0.104J, producing another broad specific heat peak for a crossover to a bosonic quantum Coulomb liquid, where the spin correlation contains both photon and quantum spin-ice monopole contributions. With negatively increasing J ⊥ across J ⊥c , a first-order thermal phase transition occurs from the quantum Coulomb liquid to an XY ferromagnet. Relevance to magnetic rare-earth pyrochlore oxides is discussed.

In the search for quantum spin liquids, candidate materials for the Kitaev model and its extensions have been intensively explored during the past decade, as the models realize the exact quantum spin liquids in the ground state. Thus far, insulating magnets in the low-spin d 5 electron configuration under the strong spin-orbit coupling have been studied for realizing the Kitaev-type bond-dependent anisotropic interactions between the spin-orbital entangled Kramers doublets. To extend the candidates, here we investigate the systems in a high-spin d 7 electron configuration, whose ground state is described by the spin-orbital entangled Kramers doublet. By the secondorder perturbation in terms of the t 2g -t 2g and t 2g -e g hoppings, we show that the effective spin model possesses the anisotropic Kitaev interactions as well as the isotropic Heisenberg ones. While the Kitaev interaction is always ferromagnetic, the Heisenberg interaction can become either ferromagnetic or antiferromagnetic depending on the Coulomb interactions and the crystalline electric fields. We also derive the effective model for the low-spin d 5 electron configuration within the same perturbation scheme, in which the Kitaev interaction becomes both ferromagnetic and antiferromagnetic, while the Heisenberg one always ferromagnetic. Referring to the previous study for the Kitaev-Heisenberg model, we find that the quantum spin liquid phase exists in the reasonable parameter region in both d 7 and d 5 cases, while the former has a richer structure of the phase diagram. We discuss the advantages of the d 7 case in comparison with the d 5 case. Our results indicate that the high-spin d 7 state provides another platform for the Kitaev-type quantum spin liquid.