Magnetic and transport properties of colossal magnetoresistance compound EuB 6
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TURE SOLID-STATE PHYSICS
Magnetic and Transport Properties of Colossal Magnetoresistance Compound EuB6 V. V. Glushkova, A. V. Bogacha, K. V. Gon’kova, S. V. Demisheva, V. Yu. Ivanova, A. V. Kuznetsovb, N. A. Samarina, N. Yu. Shitsevalovac, K. Flachbartd, and N. E. Sluchankoa a Prokhorov
General Physics Institute, Russian Academy of Sciences, Moscow, 119991 Russia e-mail: [email protected] b Moscow Institute of Engineering Physics, Kashirskoe sh. 31, Moscow, 115409 Russia c Institute for Problems in Materials Science, National Academy of Sciences of Ukraine, ul. Krzhizhanovskogo 3, Kiev, 03680 Ukraine d Centre of Low Temperature Physics, IEP SAS and IPS FS UPJS, Kosice, SK-04001 Slovakia
Abstract—The galvanomagnetic and magnetic properties of EuB6 single crystal have been measured over wide temperature (1.8–300 K) and magnetic-field (up to 70 kOe) ranges, and the parameters of charge carriers and the characteristics of the magnetic subsystem are estimated in the paramagnetic and ferromagnetic (T < TC ≈ 13.9 K) phases of this compound with strong electron correlations. In the temperature range T < T* ≈ 80 K, a magnetoresistance hysteresis ∆ρ(H)/ρ(0) is detected; it reaches a maximum amplitude of about 5% at T ≈ 12 K. The anomalies of charge transport observed in the temperature range TC < T < T* are shown to be related to the magnetic scattering of charge carriers (meff = (15–30)m0, where m0 is the free-electron mass) that results from a short-range magnetic order appearing upon the formation of ferromagnetic nanoregions (ferrons). PACS numbers: 71.30.+h, 75.47.-m DOI: 10.1134/S1063776107070278
Although europium hexaboride has been studied for a long time, the nature of the anomalies in the low-temperature properties of this semimetal with a simple cubic structure is still incompletely understood [1–10]. In particular, the colossal magnetoresistance observed in the vicinity of the metal-semiconductor transition [2] is considered to be related to magnetic polarons forming in the EuB6 matrix in the vicinity of the transition into the ferromagnetic phase [3, 4]. The difference in temperatures of transition to the metallic phase (Tm = 12.5–15.3 K) and ferromagnetic ordering (TC = 9–12.7 K) [2, 5] also indicates possible realization of the state with electronic and magnetic phase separation at T < Tm that was detected in experiments on polarized-muon scattering [6]. However, the choice of an adequate approach to describing the anomalous properties of this compound with strong electronic correlations [9] is substantially hampered by a universal relation between the magnetization and plasma frequency [7] and the absence of significant changes in the topology and sizes of the Fermi surface during the transition into the lowtemperature metallic state of EuB6 [8]. To obtain information on the characteristics of the paramagnetic and ferromagnetic phases of europium hexaboride, we studied the transport and magnetic properties of EuB6 single crystals over wide temperature (1.8–300 K) and magnetic-field (up to 70 kOe)
ranges.
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