Strain-induced magnetic phase transition inSrCoO3−δthin films

Abstract

It has been well established that both in bulk at ambient pressure and for films under modest strains, cubic SrCoO 3−δ (δ < 0.2) is a ferromagnetic metal. Recent theoretical work, however, indicates that a magnetic phase transition to an antiferromagnetic structure could occur under large strain accompanied by a metal-insulator transition. We have observed a strain-induced ferromagnetic to antiferromagnetic phase transition in SrCoO 3−δ films grown on DyScO3 substrates, which provide a large tensile epitaxial strain, as compared to ferromagnetic films under lower tensile strain on SrTiO3 substrates. Magnetometry results demonstrate the existence of antiferromagnetic spin correlations and neutron diffraction experiments provide a direct evidence for a G-type antiferromagnetic structure with Neél temperatures between TN ∼ 135 ± 10 K and ∼ 325 ± 10 K depending on the oxygen content of the samples. Therefore, our data experimentally confirm the predicted strain-induced magnetic phase transition to an antiferromagnetic state for SrCoO 3−δ thin films under large epitaxial strain.The broad range of transition metal oxide functionalities, including superconductivity, magnetism, and ferroelectricity, can be tuned by the careful choice of parameters such as strain, oxygen content, or applied electric and magnetic fields 1-9 . This tunability makes transition metal oxide materials ideal candidates for use in developing novel information and energy technologies 10,11 . SrCoO 3 is a particularly interesting system for investigation. SrCoO 3−δ has long been studied due to its propensity to form oxygen-vacancy-ordered structures as the oxygen content is decreased. The system undergoes well-defined structural phase transitions between distinct topotactic phases, from a cubic perovskite phase at SrCoO 3 to brownmillerite SrCoO 2.5 . The ties between the structural and functional properties of the material are obvious as a magnetic phase transition from ferromagnetic (FM) SrCoO 3.0 with T C = 280-305 K to antiferromagnetic (AFM) SrCoO 2.5 with T N = 570 K accompanies the structural transition 5,[12][13][14] . This is similar to the case of SrFeO 3−δ , which has also been demonstrated to undergo oxygen vacancy ordering with magnetic phase transitions related to the structure and Fe charge ordering [17][18][19] .In addition to oxygen stoichiometry, other possibilities, such as strain or applied magnetic or electric fields, may be used to tune the system. Lee and Rabe have simulated the effect of epitaxial strain on SrCoO 3.0 and predict a large polar instability resulting in a dependence of the magnetic structure on strain 20,21 . Their results show that the magnetic state can be controlled by the amount of compressive or tensile strain applied. An AFM-FM transition is predicted at both, tensile strain of ∼2.0 % and compressive strain of approximately -0.8 %, which is caused through the Goodenough-Kanamori rules as a consequence of simultaneous structural phase transitions between phases with different distortions and rotational pa...

Revisiting the zero-temperature phase diagram of stoichiometric SrCoO3 with first-principles methods

“…These theoretical results suggest that large magnetoelectric effects, that is, cross responses to applied electric and magnetic fields, could be realised in SCO thin films, as in regions where several multiferroic phases are energetically competitive those can be expected to happen [57,58]. In two recent experimental studies on SrCoO 3−δ thin films by Callori et al [26] and Hu et al [27], the existence of an antiferromagnetic phase at moderate tensile strains of ∼ +2.7 % has been ascertained; however, the accompanying metal-to-insulator and nonpolar-to-ferroelectric phase transitions as predicted by Lee and Rabe appear to be missing. The second multiferroic phase transformation that has been anticipated to occur at compressive strains also remains experimentally unverified, in spite of the small epitaxial distortions that have been suggested to be involved (i. e., ∼ −1 %) [29,30].…”

Epitaxial Oxides on Semiconductors: From Fundamentals to New Devices

“…Tuning of electronic properties of oxides through structural changes has been studied extensively in epitaxial films, in which compressive or tensile strain can be imposed via the substrate, and also in bulk single crystals . Examples include the enhancement of ferroelectricity in BaTiO 3 , control of ferromagnetism in SrCoO 3–δ , and the tuning of superconductivity in Sr 2 RuO 4 …”

Exchange bias and inverted hysteresis in monolithic oxide films by structural gradient

“…Another approach in diversifying the physical properties is the creation of gradient phases in which the composition or the corner-connected oxygen-octahedral network continuously changes across the thin film. Examples are monolithic thin films of LaCoO 3-x , La 2/3 Sr 1/3 MnO 3-x , and SrCoO 3-x , where large-scale oxygen vacancy migration or creation, topotactic structural phase transition [21,23,24], and spin state manipulation [17,24,25] have been observed. Change related to oxygen octahedra is the one key factor that is shared between all mentioned physical phenomena.…”