Interface-induced spontaneous positive and conventional negative exchange bias effects in bilayer La0.7Sr0.3MnO3/Eu0.45Sr0.55MnO3 heterostructures

Abstract

We report zero-field-cooled spontaneous-positive and field-cooled conventional-negative exchange bias effects in epitaxial bilayer composed of La0.7Sr0.3MnO3 (LSMO) with ferromagnetic (FM) and Eu0.45Sr0.55MnO3 (ESMO) with A-type antiferromagnetic (AF) heterostructures respectively. A temperature dependent magnetization study of LSMO/ESMO bilayers grown on SrTiO3 (001) manifest FM ordering (TC) of LSMO at ~320 K, charge/orbital ordering of ESMO at ~194 K and AF ordering (TN) of ESMO at ~150 K. The random field Ising model has demonstrated an interesting observation of inverse dependence of exchange bias effect on AF layer thickness due to the competition between FM-AF interface coupling and AF domain wall energy. The isothermally field induced unidirectional exchange anisotropy formed at the interface of FM-LSMO layer and the kinetically phase-arrested magnetic phase obtained from the metamagnetic AF-ESMO layer could be responsible for the spontaneous exchange bias effect. Importantly, no magnetic poling is needed, as necessary for the applications. The FM-AF interface exchange interaction has been ascribed to the AF coupling with (, coupling constant between AF spins) for the spontaneous positive hysteresis loop shift, and the field-cooled conventional exchange bias has been attributed to the ferromagnetically exchanged interface with (coupling constant between FM spins).

Interfacial spin glass mediated spontaneous exchange bias effect in self-assembled La0.7Sr0.3MnO3:NiO nanocomposite thin films

“…Such type of EB in the ZFC M-H loop is termed as spontaneous exchange bias (SEB). 23 In the descending branch of the M-H loop, a step like feature is also observed, suggesting the step-wise magnetic reversal process in the system. This type of spontaneous exchange bias has been earlier observed in various systems mainly in super spin glass based interface in bulk, nano composite and superlattice.…”

“…positive exchange bias where the shift in the field cooled magnetic hysteresis loop is in the same direction as the applied biasing field; 21 unconventional exchange bias where the TC of FM layer is lower than the TN of AFM layer 22 and spontaneous exchange bias (SEB) where the unidirectional exchange anisotropy at the interface is created without field cooling the system, causing EB effect in zero field cooled condition also. 23 Generally G-type (AFM) is not expected to pin the FM spin by exchange coupling because of compensated spin arrangement at the FM/AFM interface. However, recently unusual exchange bias was observed in epitaxial heterostructures comprising of FM-La0.7Sr0.3MnO3 and G-type AFM-SrMnO3, which was hugely correlated with interface spin frustration and attributed to the Dzyaloshinskii Moriya interaction.…”

Interfacial Ferromagnetic Coupling and Positive Spontaneous Exchange Bias in SrFeO3–x/La0.7Sr0.3MnO3 Bilayers

“…Experiments on the negative SEB have been mainly focused on Heusler alloys due to their high T c . − Moreover, some oxides also show the same effect, such as BiFeO 3 –Bi 2 Fe 4 O 9 nanoparticles, Pr 1– x Ca x MnO 3 nanosheets, and Ni 80 Fe 20 /Co 3 O 4 thin films . Anyway, there have been very few reports on positive SEB, such as the single-crystal DyFeO 3 /Fe heterostructure, La 0.7 Sr 0.3 MnO 3 /Eu 0.45 Sr 0.55 MnO 3 bilayer, and (La,Sr)­MnO 3 /PZT/(La,Sr)­MnO 3 sandwich structure . Up to now, the widely accepted origin of positive SEB and conventional PEB is attributed to the strong interfacial AFM coupling in FM/AFM systems. ,, However, to our knowledge, the influence of FM coupling in FM/AFM interfaces on either positive SEB or conventional PEB phenomena has never been reported and cannot be expected.…”

“…13−16 Moreover, some oxides also show the same effect, such as BiFeO 3 −Bi 2 Fe 4 O 9 nanoparticles, 17 Pr 1−x Ca x MnO 3 nanosheets, 18 and Ni 80 Fe 20 /Co 3 O 4 thin films. 19 Anyway, there have been very few reports on positive SEB, such as the single-crystal DyFeO 3 /Fe heterostructure, 20 La 0.7 Sr 0.3 MnO 3 /Eu 0.45 Sr 0.55 MnO 3 bilayer, 21 and (La,Sr)MnO 3 / PZT/(La,Sr)MnO 3 sandwich structure. 22 Up to now, the widely accepted origin of positive SEB and conventional PEB is attributed to the strong interfacial AFM coupling in FM/AFM systems.…”

A comparative investigation of normal and inverted exchange bias effect for magnetic fluid hyperthermia applications

“…7 c,d perfectly exhibits an EB phenomenon with an expansion in the coercive field (H c ) and shifting of the hysteresis loop with a field magnitude referred to as the EB field (H eb ) 19 , 54 . Interestingly, the shifting of M-H loop is observed along the negative field 20 , 54 , 55 for inverted NF with an EB field H eb = − 329.43 Oe, while the M–H loop is shifted along the positive field 15 , 56 , 57 with H eb = + 126 Oe for FN system. The variation of H eb with temperature for both the CS nanostructure is shown in Fig.…”