Unconventional switching behavior in La0.7Sr0.3MnO3/La0.7Sr0.3CoO3 exchange-spring bilayers

Abstract

We report on the observation of exchange-spring behavior in complex oxide bilayers composed of high coercivity ferromagnetic (FM) La 0.7 Sr 0.3 CoO 3 (LSCO) and low coercivity FM La 0.7 Sr 0.3 MnO 3 (LSMO). The magnetization process from each individual layer is revealed by a combination of bulk magnetometry and x-ray magnetic circular dichroism measurements. The results show unexpected magnetic switching behavior which deviates from conventional exchange-spring systems in that reversible switching occurs not only within the soft LSMO layer but is also accompanied by the switching of an interfacial LSCO layer. The origin of such exchange coupling is discussed in terms of charge redistribution at the interface. V C 2014 AIP Publishing LLC.

Tuning interfacial exchange interactions via electronic reconstruction in transition-metal oxide heterostructures

“…These results provide direct evidence of FM exchange interactions at the LSMO/LSCO interface similar to EB effects at FM/ AFM interfaces. 8 This EB-behavior persists in sample CM17 with much thicker layers. The same biasing scheme was employed with the XMCD hysteresis loops.…”

“…Similarly, heterostructures composed of soft and hard FM layers can exhibit EB effects characterized by a unidirectional magnetic anisotropy induced by exchange interactions. [8][9][10][11] The aim of this work is to perform a detailed investigation into the magnetic spin/electronic structures, which develop at interfaces in La 0.7 Sr 0.3 MnO 3 (LSMO)/La 0.7 Sr 0.3 CoO 3 (LSCO) heterostructures grown on (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 (LSAT) substrates. LSMO is a soft FM metal that shows coincident FM-to-PM and metal-to-insulator transitions at 360 K. 12,13 In bulk form, La 1-x Sr x CoO 3 with x < 0.22 displays magnetoelectronic phase separation (MEPS), [14][15][16] where FM/metallic clusters are embedded in a non-magnetic/insulating matrix.…”

“…The magnetic transitions at 0.002 T and 0.6 T correspond well with the coercivity of the soft LSMO and hard LSCO layers, respectively. 8 In order to investigate the exchange interactions between the two layers, minor loops were measured where the samples were first biased at 61.8 T to reach full saturation, and then loops were measured between 60.2 T. This smaller field induces switching only in the soft layer. The biased minor loops (Fig.…”

“…These findings indicate that the LSCO layer is composed of two magnetic phases, the expected magnetically hard phase and a soft phase strongly coupled to the LSMO layer. 8 To understand the physical origin of the interfacial exchange interactions, the electronic structure of the heterostructures were investigated using XA/XMCD spectroscopy. Co/Mn L-edge XA spectra involve excitation of electrons from filled 2p to empty 3d states, and provide information on valence states and bonding environments of transition metal ions.…”

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“…With the TEY measurements, the Mn-XA/XMCD signal emanates primarily from the portion of the LSMO sublayer in proximity to the top LSMO/LSCO interface, and the signal could not be detected above the noise floor for the m > 12 SLs. For the m ⩽ 12 SLs, the interface-sensitive Mn-XA spectra resembles that of the LSCMO film and differs from LSMO [40][41][42][43][44]. However, as with the Co-XMCD spectra, the spectral shape of the Mn-XMCD curves remains unchanged, indicating that the magnetically active Mn 3+ /Mn 4+ ions remain largely as in the thick LSMO film though they are broken up by a higher concentration of Mn 4+ ions.…”