Magnetic reversal and relaxation in La-Ca-Mn-O based exchange-biased multilayers

Ioannis Panagiotopoulos 3Nikolaos Moutis 1Christos Christides 2

1. Institute of Materials Science "Demokritos", 15 310 Ag.Paraskevi, Athens 153 10, Greece
2. Department of Engineering Sciences, School of Engineering, University of Patras, Patras 26 110, Greece
3. Department of Materials Science and technology, University of Ioannina, Ioannina 45110, Greece

Abstract

In mixed valence manganese perovskites the competition between the various types of interactions as double exchange, Jahn-Teller coupling, Coulomb, and antiferromagnetic superexchange which are sensitive to the structural parameters and doping creates a rich phase diagram with various types of magnetic, orbital and charge ordering. Thus they present an ideal system for building exchange-biased antiferromagnetic (AF), ferromagnetic FM superlattices since the structural compatibility of the AF and FM layers permits coherent growth of the superlattice that satisfy the conditions for magnetic coupling at the interfaces.
Magnetic and magnetotransport measurements in La-Ca-Mn-O based FM/AF multilayers prepared by pulsed laser magnetic measurements have revealed the presence of an exchange-biasing mechanism at low temperatures.
The blocking temperature (TB) distribution has been estimated by the dependence of HEB on a field cooling process that includes field reversal at a intermediate temperatures. The derived TB distribution as well as the exponential thermal decay of HEB can be attributed to to the competing interactions and phase separation at the AF/FM interfaces that give rise to a spin-glass-like magnetic disorder.
The asymmetry of the magnetization reversal has been probed by (i) magnetoresistance measurements (ii) temperature dependence of the left and right coercive fields (iii) and magnetic viscosity measurements.
The magnetic relaxation follows a ln(t) dependence at 5 K, which is a universal feature of a slow relaxation process, whereas above the blocking temperature of TB=70K the time decay requires an additional exponential term. Below TB, the observed loop asymmetries in the irreversible susceptibility and the magnetic viscosity S reveal two inequivalent reversal mechanisms between the field increasing and field decreasing branches of the hysteresis loop.

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Presentation: invited oral at E-MRS Fall Meeting 2003, Symposium D, by Ioannis Panagiotopoulos
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-16 10:54
Revised:   2009-06-08 12:55
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