Enhanced room-temperature magnetoresistance in self-assembled Ag-coated multiphasic chromium oxide nanocomposites

Abstract

Self-assembled Ag-coated multiphasic diluted magnetic chromium oxide nanocomposites were developed by a facile chemical synthesis route involving a reaction of CrO3 in the presence of Ag(+) ions in an aqueous solution of poly-vinyl alcohol (PVA) and sucrose. The tiny ferromagnetic single domains of tetragonal and orthorhombic CrO2 (t-CrO2 and o-CrO2) embedded in a dominantly insulating matrix of antiferromagnetic Cr2O3 and Cr3O8, and paramagnetic CrO3 and Cr2O, with a correlated diamagnetic thin and discontinuous shell layer of Ag efficiently tailor useful magnetic and room-temperature magnetoresistance (RTMR) properties. The t-CrO2, o-CrO2, possible canted ferromagnetism due to spin disorder in the matrix components, and the associated exchange interactions are the elements responsible for the observed ferromagnetism in the composite structure. The chain of ferromagnetic centers embedded in the composite matrix constitutes a type of magnetic tunnel junction through which spin-polarized electrons can effectively move without significant local interruptions. Electrical transport measurements showed that the spin-dependent tunneling (SDT) mechanism in the engineered microstructure of the nanocomposites exists even at room temperature (RT). A typical sample unveils a markedly enhanced RTMR-value, e.g., -80% at an applied field (H) of 3 kOe, compared to the reported values for compacted CrO2 powders or composites. The enhanced RTMR-value observed in the Coulomb blockade regime appears not only due to the considerably suppressed spin flipping at RT but primarily due to a highly effective SDT mechanism through an interlinked structure of Ag-coated multiphasic chromium oxide nanocomposites.

Effect of Cr Concentration on the Optical and Magnetic Properties of Cr‐TiN Thin Films Grown by Reactive Magnetron Sputtering

“…While chromium metal and chromium nitride are antiferromagnetic, chromium dioxide (CrO 2 ) is ferromagnetic, and Cr 2 O 3 and CrO 3 are antiferromagnetic and paramagnetic, respectively. [ 33,34 ] Hence, the observed ferromagnetic signal in samples S3 and S7 could not be due to CrO 2 clusters because no CrO 2 phases were found in the XPS spectra as shown in Figure 5e. Hence, the origin of ferromagnetism in our films with low Cr concentration (as S3) could be due to long‐range ferromagnetic ordering of chromium atoms acting as bound magnetic polarons (BMP).…”

Investigation of temperature dependence of magnetic properties of Cr$_2$O$_3$ thin film structure using a magnetic field imaging technique based on Nitrogen-Vacancy centres in diamond crystal

“…In this work we apply the magnetic field imaging technique to measure the changes in magnetic properties at phase transitions of Cr 2 O 3 thin film structures. Cr 2 O 3 is used in a number of thin film and nonstructural applications: changing magnetic properties of multilayer thin film systems [13][14][15][16], enhanced magnetoresistance properties [16][17][18], magnetoelectric random access memory [19], spin-current research [20,21] and even exotic spin superfluid research [22]. This material is favorable for a number of properties: relatively high magnetic susceptibility +1960 • 10 −6 cm 3 /mol, easy to reach NÃľel temperature at 34 • C and with it transition from antiferromagnetic to paramagnetic properties.…”