Grupo de Materiales Magnéticos (GMM). Universidad de Castilla-La Mancha

The nanostructured magnetic systems, as, e.g., multilayers, nanoparticles and granular films (dispersion of nanoparticles in a solid matrix), have been recently deeply studied in order to better understand two physical processes that determine the thermal stability of nanomagnets (crucial for increasing the storage density in hard disks) in addition of the obvious influence of their size: the interaction between particles (dipolar and/or RKKY in metallic matrix) and the exchange bias in nanoparticles with core-shell structure (ferromagnetic core and antiferromagnetic shell or matrix). In a complementary way, this second phenomenon is also studied in the multilayer geometry, configuration used indeed in most of the applications (e.g.: spin valves in reader heads).

On the other hand, the multilayers of transition metals and rare earths are especially relevant for the study of magnetic interactions, as both materials have an anti-parallel coupling between them, giving place to an artificial ferrimagnet (i.e., a multilayer acting as an ferrimagnetic material but with anti-parallel coupling between the layers, not the atoms).

Additionally, depending on the Curie temperature of the materials, the temperature and the applied field, many interesting magnetic states (exchange spring, spin flop, etc.) can be obtained.

The Magnetic Materials Group of the UCLM has a broad experience in the preparation (by sputtering and also recently with a cluster gun) and characterization of the commented materials by SQUID magnetometry, X-ray and neutron scattering, and magneto-transport measurements.

Personnel

• Researchers: José Manuel Riveiro Corona, Juan Pedro Andrés González, Juan Antonio González Sanz, Pablo Muñiz García, José Ángel de Toro Sánchez, Peter S. Normile, Ricardo López Antón.
• Technicians: Mario Rivera Cabanillas, Eduardo Prado García-Consuegra.

Research lines:

• Magnetic nanoparticle systems.
• Exchange bias in nanostructured systems.
• Magnetic interaction in multilayers of transition metals and rare earths.

Current facilities and infrastructure:

Synthesis:

• Ultra high vacuum spherical chamber with:
• Two magnetron sputtering sources for RF/DC operation (3'').
• Cluster gun (Mantis) with DC magnetron sputtering source (2'').
• Retractable and rotary sample holder.
• Retractable crystal quartz monitor (Sycon instruments STC-2000A).
• Sputtering Leybold Z400 with three magnetron sputtering sources for RF/DC operation (3'') and heated sample holder up to 600ºC
• Sputtering Boc-Edwards with three magnetron sputtering sources for RF/DC operation (3'') and computer controlled movement for multilayer deposition.
• Planetary ball mill (Retsch 4) for mechanical alloying and amorphization process.

Characterization:

• Magnetometers:
• SQUID (QD MPMS-XL Evercool), field up to 5 T and DC/AC measurements.
• Vibrating simple magnetometer VSM (LDJ 9600) with Helium cryostat and oven.
• MagLab EXA (Oxford), DC measurements, field up to 9T and sample holder for electrical transport measurements.
• X ray diffractometer(Bruker D8 Advance), Theta-Theta geometry, powder diffraction and reflectivity measurements, LynxEye detector.
• Scanning electron microscope SEM(Philips XL30) with EDX analysis.
• Closed-cycle Helium refrigerator for electrical transport measurements(10-300 K).
• Differential scanning calorimeter DSC(Perkin-Elmer).

Research projects:

• "High sensibility SQUID magnetometer", FEDER (UNCM08-1E-022). Amount granted: 249.760 €.
• "Magnetic properties in nanogranular composites: control through the matrix/Propiedades", Ministerio de Economía y Competitividad/Spanish Ministry of Economy and Competitivity (MAT2011-26207). Amount granted: 60.000 €.

Selection of recent publications (in the last 5 years):

• "Phase transition in a super superspin glass". R. Mathieu, J. A. De Toro, D. Salazar, S. S. Lee, J. L. Cheong, P. Nordblad. EPL – Europhysics Letters (en prensa).
• "Controlled close-packing of ferrimagnetic nanoparticles: an assessment of the role of interparticle superexchange versus dipolar interactions". J. A. De Toro, P. S. Normile, S. S. Lee, D. Salazar, J. L. Cheong, , P. Muñiz, J. M. Riveiro, M. Hillenkamp, F. Tournus, A. Tamion, and P. Nordblad. Journal of Physical Chemistry C (en prensa).
• "A nanoparticle replica of the spin-glass state". J. A. De Toro, S. S. Lee, D. Salazar, J. L. Cheong, P. S. Normile, P. Muñiz, J. M. Riveiro, M. Hillenkamp, F. Tournus, A. Tamion, and P. Nordblad Applied Physics Letters 102, 183104 (2013)
• "Comment on "Accurate determination of the magnetic anisotropy in cluster-assembled nanostructures" [Appl. Phys. Lett. 95, 062503 (2009)] Normile, P. S.; De Toro, J. A. Applied Physics Letters 100,13610 (2012)
• "Energy barrier enhancement by weak magnetic interactions in Co/Nb granular films assembled by inert gas condensation". J. A. De Toro, J. A. González, P. S. Normile, P. Muñiz, J. P. Andrés, R. López-Antón, J. M. Riveiro, J. Canales-Vázquez. Physical Review B 85, 054429 (2012).
• "2D Crystallography introduced by the sprinkler watering problem". J. A. De Toro, G. F. Calvo, P. Muñiz. European Journal of Physics 33, 167 (2012).
• "Role of the oxygen partial pressure in the formation of composite Co–CoO nanoparticles by reactive aggregation". J. A. De Toro, J. P. Andrés, J. A. González, J. M. Riveiro, M. Estrader, A. López–Ortega, I. Tsiaoussis, N. Frangis, J. Nogués. Journal of Nanoparticle Research 13, 4583 (2011).
• "Tracking the Evolution of Magnetic Ordering in Co/Ru Multilayers with Inhomogeneous Interlayer Coupling using Polarised Neutron Reflectometry". Autores: J A González, L.-A. Michez, T. R. Charlton, B. J. Hickey, S. Langridge and C. H. Marrows. Revista: Physica B 406 (13) , 2689 (2011).
• "Origin of the giant magnetic moment in epitaxial Fe3O4 thin films". J. Orna, P.A. Algarabel, L. Morellón, J.A. Pardo, J.M. de Teresa, R. López Antón, F. Bartolomé, L. M. García, J. Bartolomé, J. C. Cezar, A. Wildes. Physical Review B 81, 144420 (2010).
• "Co-CoO Nanoparticles Prepared by Reactive Gas-Phase Aggregation". J. A. González, J. P. Andrés, J. A. De Toro, P. Muñiz, T. Muñoz, J. M. Riveiro. Journal of Nanoparticle Research 11, 2105 (2009).
• "The oxidation of metal-capped Co cluster films at ambient conditions". J. A. De Toro, J. P. Andrés, J. A. González, P. Muñiz, J. M. Riveiro. Nanotechnology 20, 085710 (2009).
• "CoO1-layers in a reactively sputtered exchange bias system". J. M. Riveiro, P. S. Normile, J. A. De Toro, T. Muñoz, P. Muniz, J. A. González, J. P. Andrés. New Journal of Physics 10, 083028 (2008).
• "Artificial ferrimagnetic structure and thermal hysteresis in Gd0.47Co0.53/Co multilayers". Autores: J.P. Andrés, J. A. González, J.M. Riveiro, T.P.A. Hase, B. K. Tanner. Physical Review B 77, 144407 (2008).

Publications obtained from collaborations with other colleagues from the network):

• Study of GdCo/Si/Co/Si Multilayers by Polarized Neutron Reflectivity" R. López Antón, A.V. Svalov, J.M. Barandiarán, T.R. Charlton, M. Krzystyniak and G.V. Kurlyandskaya Journal of Physics: ConferenceSeries 325 (2011) 012018.
• "Influence of the preparation procedure on the properties of polyaniline based magnetic composites" J.C. Aphesteguy, S.E. Jacobo, R. Lopez Anton, N.N. Schegoleva, G.V. Kurlyandskaya European Polymer Journal 43 (2007) 1333-1346.
• "Coupling between Co and Gd–Co layers separated by nonmagnetic spacers" A.V. Svalov, A. Fernandez, V.O. Vas’kovskiy, R. Lopez Anton, J.M. Barandiaran, M. Tejedor and G.V. Kurlyandskaya Physica B: Condensed Matter 396 (2007) 113-116.