CMag

Recent Research

• Broken ergodicity, memory effect, and rejuvenation in Taylor-phase and decagonal Al3(Mn, Pd, Fe) complex intermetallics: J. Dolinšek, J. Slanovec, Z. Jagličić, M. Heggen, S. Balanetskyy, M. Feuerbacher, K. Urban, PRB, 77 (2008) 064430-1 Dolinsek J, Jaglicic Z, Chernikov MA, Fisher IR, Canfield PC PHYSICAL REVIEW B 6422 (22): art. no. 224209 DEC 1 2001

  Abstract: The Taylor-phase complex intermetallic compound T-Al3Mn, its solid solutions with Pd and Fe, T-Al3(Mn,Pd) and T-Al3(Mn,Fe), and the related decagonal d-Al-Mn-Fe quasicrystal belong to the class of magnetically frustrated spin systems that exhibit rich out-of-equilibrium spin dynamics in the nonergodic phase below the spin-freezing temperature Tf. Performing large variety of magnetic experiments as a function of temperature, magnetic field, aging time tw, and different thermal histories, we investigated broken-ergodicity phenomena of (i) a difference in the field-cooled and zero-field-cooled susceptibilities, (ii) the frequencydependent freezing temperature, Tf, (iii) hysteresis and remanence, (iv) ultraslow decay of the thermoremanent magnetization, (v) the memory effect (a state of the spin system reached upon isothermal aging can be retrieved after a negative temperature cycle), and (vi) “rejuvenation” (small positive temperature cycle within the nonergodic phase erases the effect of previous aging). We show that the phenomena involving isothermal aging periods (the memory effect, rejuvenation, and the ultraslow decay of the thermoremanent magnetization) get simple explanation by considering that during aging under steady external conditions, localized spin regions quasiequilibrate into more stable configurations, so that higher thermal energy is needed to destroy these regions by spin flipping, as compared to the thermal energy required to reverse a frustrated spin in a disordered spin-glass configuration that forms in the case of no aging. Common to all the investigated brokenergodicity phenomena is the slow approach of a magnetically frustrated spin system toward a global equilibrium, which can never be reached on accessible experimental time scales due to macroscopic equilibration times.

• Nonaqueous Synthesis of Manganese Oxide Nanoparticles, Structural Characterization, and Magnetic Properties: I. Djerdj, D. Arčon, Z. Jagličić, M. Niederberger: J. Phys. Chem. C, 111 (2007) 3614-3623.

  Abstract: The synthesis, structural characterization, and magnetic properties of crystalline manganese oxide nanoparticles are presented. The procedure is based on the reaction of benzyl alcohol with the two precursors: potassium permanganate KMnO4 and manganese(II) acetylacetonate Mn(acac)2. Depending on the precursor used, the composition of the final product can be varied in such a way that in the case of KMnO4 mainly Mn3O4 is formed, whereas Mn(acac)2 leads predominantly to MnO. Rietveld refinement of the XRD powder patterns, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and energy-dispersive X-ray (EDX) analysis, as well as electron energy loss spectroscopy (EELS) were employed for the structural characterization of the as-synthesized compounds. Especially the MnO manganosite nanocrystals exhibit some interesting features. HRTEM investigations point to the formation of a superstructure, which can be described as an ordered Mn vacancy cubic superstructure with the general formula of Mn0.875Ox and a lattice parameter of 8.888 A. The SQUID measurement proves a superparamagnetic behavior of the MnO nanoparticles.

• Unusual magnetic state in lithium-doped MoS2 nanotubes: Mihailovic D, Jaglicic Z, Arcon D, Mrzel A, Zorko A, Remskar M, Kabanov VV, Dominko R, Gaberscek M, Gomez-Garcia CJ, Martinez-Agudo JM, Coronado E PHYSICAL REVIEW LETTERS 90 (14): art. no. 146401 APR 11 2003

  Abstract: We report on the very peculiar magnetic properties of an ensemble of very weakly coupled lithium-doped MoS2 nanotubes. The magnetic susceptibility chi of the system is nearly 3 orders of magnitude greater than in typical Pauli metals, yet there is no evidence for any instability which would alleviate this highly frustrated state. Instead, the material exhibits peculiar paramagnetic stability down to very low temperatures, with no evidence of a quantum critical point as T --> 0 in spite of clear evidence for strongly correlated electron behavior. The exceptionally weak intertube interactions appear to lead to a realization of a near-ideal one-dimensional state in which fluctuations prevent the system from reordering magnetically or structurally.