Based on low temperature resistivity, heat capacity and magnetization investigations we show that the unusually strong suppression of superconductivity in LuxZr1−xB12 BSC-type superconductors in the range x<0.08 is caused by the emergence of static spin polarization in the vicinity of nonmagnetic lutetium impurities. The analysis of received results points to a formation of static magnetic moments with µ ef f ≈3µB per Lu-ion. The size of these spin polarized nanodomains was estimated to be about 5Å.

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The magnetoresistance (MR) ρ/ρ of the cage-glass compound Ho x Lu 1−x B 12 with various concentrations of magnetic holmium ions (x 0.5) has been studied in detail concurrently with magnetization M(T ) and Hall effect investigations on high-quality single crystals at temperatures 1.9-120 K and in magnetic field up to 80 kOe. The undertaken analysis of ρ/ρ allows us to conclude that the large negative magnetoresistance (nMR) observed in the vicinity of the Néel temperature is caused by scattering of charge carriers on magnetic clusters of Ho 3+ ions, and that these nanosize regions with antiferromagnetic (AF) exchange inside may be considered as short-range-order AF domains. It was shown that the Yosida relation − ρ/ρ ∼ M 2 provides an adequate description of the nMR effect for the case of Langevin-type behavior of magnetization. Moreover, a reduction of Ho-ion effective magnetic moments in the range 3-9 μ B was found to develop both with temperature lowering and under the increase of holmium content. A phenomenological description of the large positive quadratic contribution ρ/ρ ∼ μ 2 D H 2 which dominates in Ho x Lu 1−x B 12 in the intermediate temperature range 20-120 K allows us to estimate the drift mobility exponential changes μ D ∼ T −α with α = 1.3-1.6 depending on Ho concentration. An even more comprehensive behavior of magnetoresistance has been found in the AF state of Ho x Lu 1−x B 12 where an additional linear positive component was observed and attributed to charge-carrier scattering on the spin density wave (SDW). High-precision measurements of ρ/ρ = f (H,T ) have allowed us also to reconstruct the magnetic H-T phase diagram of Ho 0.5 Lu 0.5 B 12 and to resolve its magnetic structure as a superposition of 4f (based on localized moments) and 5d (based on SDW) components.

The model strongly correlated electron system Ho 0.8 Lu 0.2 B 12 which demonstrates a cooperative Jahn-Teller instability of the boron sub-lattice in combination with rattling modes of Ho(Lu) ions, dynamic charge stripes and unusual antiferromagnetic (AF) ground state has been studied in detail at low temperatures by magnetoresistance (Δρ/ρ), magnetization and heat capacity measurements. Based on received results it turns out that the angular H-φ-T magnetic phase diagrams of this non-equilibrium AF metal can be reconstructed in the form of a "Maltese cross". The dramatic AF ground state symmetry lowering of this dodecaboride with fcc crystal structure can be attributed to the redistribution of conduction electrons which leave the RKKY oscillations of the electron spin density to participate in the dynamic charge stripes providing with extraordinary changes in the indirect exchange interaction between magnetic moments of Ho 3+ ions and resulting in the emergence of a number of various magnetic phases. It is also shown that the two main contributions to magnetoresistance in the complex AF phase, the (i) positive linear on magnetic field and the (ii) negative quadratic -Δρ/ρ~H 2 component can be separated and analyzed quantitatively, correspondingly, in terms of charge carrier scattering on spin density wave (5d) component of the magnetic structure and on local 4f-5d spin fluctuations of holmium sites. PACS: 72.15.Qm, 72.15.Gd I. INTRODUCTION. The complexity of strongly correlated electron systems (SCES) is a subject of active debates, and numerous investigations have been carried out to clarify its nature [see e.g. [1-2]).In recent years it was demonstrated that at least some of SCES are spatially inhomogeneous materials and that their electronic complexity arises from charge, spin, lattice and orbital degrees of freedom which act simultaneously, leading to giant responses at small perturbations [1-5].Moreover, when several metallic and insulating phases compete, it creates the potential for novel behavior and practical applications, and well-known examples of it are the Mn oxides called manganites [1,[6][7][8][9][10][11][12], high temperature superconducting cuprates [1][2][3][4][13][14][15][16], iron-based pnictides and chalcogenides [4][5][17][18][19][20], etc. Among the widely discussed issues in these materials are very complicated phase diagrams with various magnetic phases and ground states in combination with diverse mechanisms responsible for their competition and stabilization [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. According to conclusions of ref. 7, the ground states diversity and mixed-phase tendencies have two origins: (i) electronic phase separation between phases with different densities that leads to nanometer scale coexisting clusters, and (ii) disorder-induced phase separation with