Nanoscale switching characteristics of nearly tetragonal BiFeO3 thin films

We have investigated the nanoscale switching properties of strain-engineered BiFeO3 thin films deposited on LaAlO3 substrates using a combination of scanning probe techniques. Polarized Raman spectral analysis indicate that the nearly-tetragonal films have monoclinic (Cc) rather than P4mm tetragonal symmetry. Through local switching-spectroscopy measurements and piezoresponse force microscopy we provide clear evidence of ferroelectric switching of the tetragonal phase but the polarization direction, and therefore its switching, deviates strongly from the expected (001) tetragonal axis. We also demonstrate a large and reversible, electrically-driven structural phase transition from the tetragonal to the rhombohedral polymorph in this material which is promising for a plethora of applications.Comment: 10 pages, 6 figure

Effects of Rare-Earth (R = Pr, Gd, Ho, Er) Doping on Magnetostructural Phase Transitions and Magnetocaloric Properties in Ni43-xRxMn46Sn11 Shape Memory Alloys

A series of rare-earth-doped Ni43-xRxMn46Sn11 (x= 0, 1 and R = Pr, Gd, Ho, Er) alloys was fabricated by arc melting, and their structural, magnetic, and magnetocaloric properties were studied through room temperature X-ray diffraction (XRD), differential scanning calorimetry, and magnetization measurements. Analysis of XRD data reveal that the alloys crystallize in the cubic L21 austenite phase structure as the major phase with a small trace of martensitic phase (MP). The martensitic transition temperature (TM) shifts to consecutive higher temperatures with the substitution of Pr, Gd, Ho, and Er. A drastic shift in TM by 60 K relative to the parent compound (TM= 195 K) was found for Ni42PrMn46Sn11. Large values of magnetic entropy changes (Δ SM) of 32 (Pr), 28 (Gd), and 25Jkg-1K-1 (Ho) were obtained at TM for Δ H = 50 kOe. A maximum value of the refrigeration capacity of ∼ 250Jkg-1 was obtained in the vicinity of TM for Δ H=50 kOe for the Ho-doped compound. A large exchange bias effect with HEB ∼ 1.1 kOe at 10 K was observed for the Pr-doped compound in its MP

Large inverse magnetocaloric effects and giant magnetoresistance in Ni-Mn-Cr-Sn heusler alloys

The magnetostructural transitions, magnetocaloric effects, and magnetoresistance properties of Ni45Mn43CrSn11 Heusler alloys were investigated using X-ray diffraction (XRD), field-dependent magnetization, and electrical resistivity measurements. A large inverse and direct magnetocaloric effect has been observed in Ni45Mn43CrSn11 across the martensitic and Curie transition temperature, respectively. The values of the latent heat (L = 15.5 J/g) and corresponding magnetic (∆SM) and total (∆ST) entropy changes (∆SM = 35 J/kg·K for ∆H = 5T and ∆ST = 39.7 J/kg·K) have been evaluated using magnetic and differential scanning calorimetry (DSC) measurements, respectively. A substantial jump in resistivity was observed across the martensitic transformation. A large negative magnetoresistance (~67%) was obtained at the magnetostructural transition for a field change of 5 T. The roles of the magnetic and structural changes on the transition temperatures and the potential application of Ni45Mn43CrSn11 Heusler alloys for refrigerator technology are discussed