No abstract

No abstract

Superlattices consist of two ferromagnets La 0.7 Sr 0.3 MnO 3 (LSMO) and SrRuO 3 (SRO) were grown in (110)-orientation on SrTiO 3 (STO) substrates. The x-ray diffraction and Raman spectra of these superlattices show the presence of in-plane compressive strain and orthorhombic structure of less than 4 u.c. thick LSMO spacer, respectively. Magnetic measurements reveal several features including reduced magnetization, enhanced coercivity, antiferromagnetic coupling, and switching from antiferromagnetic to ferromagnetic coupling with magnetic field orientations. These magnetic properties are explained by the observed orthorhombic structure of spacer LSMO in Raman scattering which occurs due to the modification in the stereochemistry of Mn at the interfaces of SRO and LSMO.

Cobalt monoxide (CoO) nanocrystals were synthesized by thermal decomposition of cobalt oleate precursor in a high boiling point organic solvent 1-octadecene. The X-ray diffraction pattern and transmission electron microscopy studies suggest that pure face-centered-cubic (fcc) phase of CoO can be synthesized in the temperature range of 569–575 K. Thermolysis product at higher synthesis temperature 585 K is a mixture of fcc and hexagonal-closed-packed (hcp) phases. These nanocrystals are single crystals of CoO and exhibit mixture of two types of morphologies; one is nearly spherical with 5–25 nm diameter, and other one is 5–10 nm thick flake. The pure fcc-CoO nanocrystals show enhanced, and mixture of fcc- and hcp-CoO nanocrystals show reduced antiferromagnetic ordering temperature. Such results provide new opportunities for optimizing and enhancing the properties and performance of cobalt oxide nanomaterials.

Interface effect in complex oxide thin film heterostructures lies at the vanguard of current research to design technologically relevant functionality and explore emergent physical phenomena. While most of the previous works focus on the perovskite/perovskite heterostructures, the study on perovskite/brownmillerite interfaces remain at its infancy. Here, we investigate spontaneously stabilized perovskite-ferromagnet (SrCoO 3-δ )/brownmillertiteantiferromagnet (SrCoO 2.5 ) bi-layer with T N > T C and discover an unconventional interfacial magnetic exchange bias effect. From magnetometry investigations, it is rationalized that the observed effect stems from the interfacial ferromagnet/antiferromagnet coupling. The possibility for coupled ferromagnet/spinglass interface engendering such effect is ruled out.Strikingly, a finite coercive field persists in the paramagnetic state of SrCoO 3-δ whereas the exchange bias field vanishes at T C . We conjecture the observed effect to be due to the effective external quenched staggered field provided by the antiferromagtic layer for the ferromagnetic spins at the interface. Our results not only unveil a new paradigm to tailor the interfacial magnetic properties in oxide heterostructures without altering the cations at the interface, but also provide a purview to delve into the fundamental aspects of exchange bias in such unusual systems paving a big step forward in thin film magnetism.1 The investigation on interfacial magnetic effects in transition metal oxide based thin film heterostructures has sparked unprecedented scientific developments and is pursued intensively because of its technological promise for the next-generation nano-scaled magnetic devices [1]. A precise control and tuning of interfacial magnetic properties in thin film heterostructures is crucial for engendering exotic functionalities which are highly relevant for technological applications such as magnetic field sensors, memories or magnetic recording read heads [2][3][4]. A great deal of attention in this regard is focused on the effect called "exchange bias" that occurs due to interfacial magnetic exchange coupling in a coupled ferromagnetic/antiferromagnetic system [5,6]. This effect is widely maneuvered for the design and operation of spin valve based magnetic read heads and sensors. The macroscopic hallmark of magnetic exchange bias effect (MEBE) is the unidirectional shift of the M(H) loop along the field-axis (Figure1(c)), and enhancement of coercivity. Typically, a bi-layer consisting of a FM and an AF (with the Curie temperature (T C ) of FM greater than the Néel temperature (T N ) of AF) when cooled in a static magnetic field across the T N , an unidirectional exchange anisotropy-fieldgets locked in and give rise to exchange bias effectthat stabilizes the orientation of the ferromagnetic layer [2,7,8]. Such systems exhibit magnetic properties that markedly differ from their constituents. Though exchange bias related phenomena in FM/AFM coupled system is studied extensively, its inherent mechanism ...