Magnetoresistance and magnetic ordering in praseodymium and neodymium hexaborides
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Magnetoresistance and Magnetic Ordering in Praseodymium and Neodymium Hexaborides M. A. Anisimova,b, A. V. Bogachb, V. V. Glushkova,b, S. V. Demishevb, N. A. Samarinb, V. B. Filipovc, N. Yu. Shitsevalovac, A. V. Kuznetsovb,d, and N. E. Sluchankob,* a
Moscow Institute of Physics and Technology (State University), Institutskiі per. 9, Dolgoprudnyі, Moscow oblast, 141700 Russia b A. M. Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia * email: [email protected] c I. N. Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, ul. Krzhizhanovskogo 3, Kiev, 03680 Ukraine d Moscow Engineering Physics Institute (State University), Kashirskoe sh. 31, Moscow, 115409 Russia Received May 22, 2009
Abstract—The magnetoresistance Δρ/ρ of singlecrystal samples of praseodymium and neodymium hexaborides (PrB6 and NdB6) has been measured at temperatures ranging from 2 to 20 K in a magnetic field of up to 80 kOe. The results obtained have revealed a crossover of the regime from a small negative magne toresistance in the paramagnetic state to a large positive magnetoresistive effect in magnetically ordered phases of the PrB6 and NdB6 compounds. An analysis of the dependences Δρ(H)/ρ has made it possible to separate three contributions to the magnetoresistance for the compounds under investigation. In addition to the main negative contribution, which is quadratic in the magnetic field (–Δρ/ρ ∝ H2), a linear positive con tribution (Δρ/ρ ∝ H) and a nonlinear ferromagnetic contribution have been found. Upon transition to a mag netically ordered state, the linear positive component in the magnetoresistance of the PrB6 and NdB6 com pounds becomes dominant, whereas the quadratic contribution to the negative magnetoresistance is com pletely suppressed in the commensurate magnetic phase of these compounds. The presence of several components in the magnetoresistance has been explained by assuming that, in the antiferromagnetic phases of PrB6 and NdB6, ferromagnetic nanoregions (ferrons) are formed in the 5d band in the vicinity of the rare earth ions. The origin of the quadratic contribution to the negative magnetoresistance is interpreted in terms of the Yosida model, which takes into account scattering of conduction electrons by localized magnetic moments of rareearth ions. Within the approach used, the local magnetic susceptibility χloc has been esti mated. It has been demonstrated that, in the temperature range TN < T < 20 K, the behavior of the local mag netic susceptibility χloc for the compounds under investigation can be described with good accuracy by the Curie–Weiss dependence χloc ∝ (T – Θp)–1. PACS numbers: 72.15.Gd, 72.15.Qm DOI: 10.1134/S1063776109110119
1. INTRODUCTION Among the promising model objects in the physics of strongly correlated electron systems, RB6 hexaborides based on rareearth elements have attracted the special interest of researchers. This is associated primarily with the fact that these
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