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Structural and magnetic properties of Fe/Pt core-shell nanostructure prepared by a sequential reduction process are reported. Transmission electron microscopy shows nearly spherical particles fitting a lognormal size distribution with Do=3.0 nm and distribution width λD=0.31. In x-ray diffraction, Bragg lines only from the Pt shell are clearly identified with line-widths yielding crystallite size=3.1 nm. Measurements of magnetization M vs. T (2K-350K) in magnetic fields up to 90 kOe show a blocking temperature TB=13K below which hysteresis loops are observed with coercivity HC increasing with decreasing T reaching HC=750Oe at 2 K. Temperature dependence of the ac susceptibilities at frequencies fm=10 Hz-5 kHz is measured to determine the change in TB with fm using the Vogel-Fulcher law. This analysis shows the presence of significant interparticle interaction, the Neel-Brown relaxation frequency fo=5.3×1010Hz and anisotropy constant Ka=3.6×106 ergs/ cm3. A fit of the M vs. H data up to H=90 kOe for T>TB to the modified Langevin function taking particle size distribution into account yields magnetic moment per particle consistent with the proposed core-shell structure; Fe core of 2.2 nm diameter and Pt shell of 0.4 nm thickness. [ABSTRACT FROM AUTHOR]

The optoelectronic and piezoelectric properties of AlN:Er thin films have been of great recent interest for potential device applications. In this work, the focus is on the electronic state of Er in AlN:Er thin films prepared by reactive magnetron sputtering on (001) p-type Si substrate. X-ray diffraction shows that Er doping expands the lattice and the AlN:Er film has preferential c-plane orientation. To determine whether Er in AlN:Er is present as Er metal, Er2O3, or Er3+ substituting for Al3+, detailed measurements and analysis of the temperature dependence (2 K-300 K) of the magnetization M at a fixed magnetic field H along with the M vs. H data at 2K up to H=90 kOe are presented. The presence of Er2O3 and Er metal is ruled out since their characteristic magnetic transitions are not observed in the AlN:Er sample. Instead, the observed M vs. T and M vs. H variations are consistent with Er present as Er3+ substituting for Al3+ in AlN:Er at a concentration x=1.08% in agreement with x=0.94%60.20% determined using x-ray photoelectron spectroscopy (XPS). The larger size of Er3+ vs. Al3+explains the observed lattice expansion of AlN:Er. [ABSTRACT FROM AUTHOR]

Experimental investigations of the magnetic dead layer in 7.6 nm thick film of La0.7Sr0.3MnO3 (LSMO) are reported. The dc magnetization (M) measurements for a sample cooled to T = 5 K in applied field H = 0 reveal the presence of negative remanent magnetization (NRM) in the M vs. H (magnetic field) measurements as well as in the M vs. T measurements in H = 50 Oe and 100 Oe. The M vs. T data in ZFC (zero-field-cooled) and FC (field-cooled) protocols are used to determine the blocking temperature TB in different H. Isothermal hysteresis loops at different T are used to determine the temperature dependence of saturation magnetization (MS), remanence (MR) and coercivity HC. The MS vs. T data are fit to the Bloch law, MS(T) = M0(1 – BT3/2), showing a good fit for T < 100 K and yielding the nearest-neighbor exchange constant J/kB ≅ 18 K. The variations of TB vs. H and HC vs. T are well described by the model often used for randomly oriented magnetic nanoparticles with magnetic domain diameter ≈ 9 nm present in the dead-layer of thickness d =1.4 nm. Finally, the data available from literature on the thickness (D) variation of Curie temperature (TC) and MS of LSMO films grown under 200, 150, and 0.38 mTorr pressures of O2 are analyzed in terms of the finite-size scaling, with MS vs. D data fit to MS(D) = MS(b)(1-d/D) yielding the dead layer thickness d = 1.1 nm, 1.4 nm and 2.4 nm respectively. Brief discussion on the significance of these results is presented. [ABSTRACT FROM AUTHOR]

A correction to the article "Co-existence of ferrimagnetism and spin-glass state in the spinel Co2SnO4" that was published in the 2013 issue is presented.

Effects of the substitution of rare-earths R=Y, Er, and Ho on the magnetic properties of Dy0.7R0.3CrO3 are reported here in order to probe the nature of magnetism and related exchange interactions in these materials. By fitting the temperature dependence of the magnetic susceptibility to a modified Curie-Weiss law, which includes a correction for the Dzyaloshinskii-Moriya (DM) interaction, the strengths of the symmetric and antisymmetric Cr3+-Cr3+ exchange interactions were determined. It was found that the rare-earth substitutions had a slight effect on the strength of the symmetric Cr3+-Cr3+ interaction (reflected in the slight changes in the Néel temperatures), while the antisymmetric Cr3+-Cr3+ interaction remained unchanged. Isothermal magnetic measurements of the samples at successive temperatures revealed a plateau in the temperature dependent magnetic coercivity data, which was explained by the magnetic properties of the substituted ions. It was found that the Y substitution led to the reduction of the strength of the magnetization and a larger peak value of magnetic coercivity as compared to that in pure DyCrO3. The observed increase in magnetic coercivity with Er and Ho substitution can be attributed to an increased R3+-Cr3+ interaction strength dominated by the DM mechanism. [ABSTRACT FROM AUTHOR]

The nature of magnetism in Er2O3 is investigated by detailed studies of the temperature (2-300 K) and magnetic field (up to 90 kOe) dependence of the magnetization M of powder sample of Er2O3. The results show paramagnetic to antiferromagnetic (AFM) transition occurring at TN=3.3 K. For T>TN = the magnetic susceptibility vs. temperature data follows the Curie-Weiss (·C/(T,TN))variation with =β-10.2 K and magnetic moment 956;=6.68μB/Er3+ ion determined from C. Molecular field model is used to determine the nn (nnn) exchange constants J1(J2)=-0.57 K (-3.38 K). The M vs. H data at 2 K analyzed in terms of dM/dH vs. H variations show two field-induced transitions, the first one at HSF∞15kOe and the second one at HS∞31kOe. Arguments and analysis are presented to show that HSF represents the spin-flop transition whereas for H HS, the system is field-aligned ferromagnetically since the calculated value of HS for ferromagnetic ordering using the above magnitudes of J1 and J2 agrees well with the experimental HS. The temperature dependence of HSF is shown to follow the normalized Brillouin function variation for spin S=1/2 valid for Er2O3. The magnetic field dependence of TN is measured and shown to follow the equation: TN(H)=TN(0)D1H², expected for antiferromagnets. [ABSTRACT FROM AUTHOR]

Observation of significant negative exchange bias (HE) is reported in solid solutions of single-phase samples of Dy1-x Ndx Cr O3 for x = 0.33,0.67, and 1 with corresponding Néel temperatures at TNCr = 175K,200K, and 225 K, respectively, and the spin-reorientation transitions TSR at 48 K, 58 K, and 38 K, respectively. In contrast, no HE was observed for the sample with x = 0 (i.e., DyCrO3) shows no HE below its TNCr = 145K, and no reorientation of spins at lower temperatures was observed. More importantly, the (negative) HE for the x = 0.33,0.67, and 1 samples is observed only in the temperature range between TN and TSR with the corresponding observation of magnetic coercivity. These results show that the canted antiferromagnetic Γ7,Cr structure of the Cr3+ moments present between TNCr and TSR is essential for the observed HE. By comparing this result to the literature, common features of single-phase materials with HE were identified. The present bulk powder samples were prepared by the citrate method and structurally characterized by x-ray diffraction and Raman spectroscopy techniques. Neutron diffraction measurements for the x = 0.33,0.67, and 1 samples at select temperatures were done to verify the presence of the Γ7,Cr structure between TNCr and TSR and the Γ1,Cr structure (with no canting of Cr3+ moments) below TSR. [ABSTRACT FROM AUTHOR]