Electrical Noise From Phase Separation In Pr2/3Ca1/3MnO3 Single Crystal

Low frequency electrical noise measurements have been used to probe the electronic state of the perovskite-type manganese oxide Pr2/3Ca1/3MnO3 versus temperature and in the vicinity of the field-induced transition from the insulating, charge-ordered state (I-CO) to the metallic, ferromagnetic state (M-F). At high temperature we have observed a high level of the excess noise with mainly a gaussian distribution of the resistance fluctuations, and the associated power spectral density has a standard 1/f dependence. However, in the hysteretic region, where the electrical resistance depends dramatically on the sample history, we have observed a huge non-gaussian noise characterized by two level fluctuator-like switching (TLS) in the time domain. We discuss the origin of the noise in terms of percolative behavior of the conductivity. We speculate that the dominant fluctuators are manganese clusters switching between the M-F and the I-CO phases.Comment: RevTeX, 6 pages with 3 figure

Spectrum of one dimensional p-Laplacian operator with indefinite weight

This paper is concerned with the nonlinear boundary eigenvalue problem $$-(|u'|^{p-2}u')'=\lambda m|u|^{p-2}u\qquad u \in I=]a,b[,\quad u(a)=u(b)=0,$$ where $p>1$, $\lambda$ is a real parameter, $m$ is an indefinite weight, and $a$, $b$ are real numbers. We prove there exists a unique sequence of eigenvalues for this problem. Each eigenvalue is simple and verifies the strict monotonicity property with respect to the weight $m$ and the domain $I$, the k-th eigenfunction, corresponding to the $k$-th eigenvalue, has exactly $k-1$ zeros in $(a,b)$. At the end, we give a simple variational formulation of eigenvalues

Nearly total spin polarization in La2/3Sr1/3MnO3 from tunneling experiments

We have performed magnetotransport measurements on La2/3Sr1/3MnO3 / SrTiO3 / La2/3Sr1/3MnO3 magnetic tunnel junctions. A magnetoresistance ratio of more than 1800 % is obtained at 4K, from which we infer an electrode spin polarization of at least 95 %. This result strongly underscores the half-metallic nature of mixed-valence manganites and demonstrates its capability as a spin analyzer. The magnetoresistance extends up to temperatures of more than 270K. We argue that these improvements over most previous works may result from optimizing the patterning process for oxide heterostructures.Comment: to appear in Applied Physics Letter

Evidence of non-degenerated, non-reciprocal and ultra-fast spin-waves in the canted antiferromagnet {\alpha}-Fe2O3

Spin-waves in antiferromagnets hold the prospects for the development of faster, less power-hungry electronics, as well as new physics based on spin-superfluids and coherent magnon-condensates. For both these perspectives, addressing electrically coherent antiferromagnetic spin-waves is of importance, a prerequisite that has so far been elusive, because unlike ferromagnets, antiferromagnets couple weakly to radiofrequency fields. Here, we demonstrate the electrical detection of ultra-fast non-reciprocal spin-waves in the dipolar-exchange regime of a canted antiferromagnet. Using time-of-flight spin-wave spectroscopy on hematite (alpha-Fe2O3), we find that the magnon wave packets can propagate as fast as 30 km/s for reciprocal bulk spin-wave modes and up to 10 km/s for surface-spin waves propagating parallel to the antiferromagnetic N\'eel vector. The electrical detection of coherent non-reciprocal antiferromagnetic spin waves holds makes hematite a versatile platform where most of the magnonic concepts developed for ferromagnet can be adapted paving the way for the development antiferromagnetic and altermagnet-based magnonic devices

Electronic control of the spin-wave damping in a magnetic insulator

It is demonstrated that the decay time of spin-wave modes existing in a magnetic insulator can be reduced or enhanced by injecting an in-plane dc current, $I_\text{dc}$, in an adjacent normal metal with strong spin-orbit interaction. The demonstration rests upon the measurement of the ferromagnetic resonance linewidth as a function of $I_\text{dc}$ in a 5~$\mu$m diameter YIG(20nm){\textbar}Pt(7nm) disk using a magnetic resonance force microscope (MRFM). Complete compensation of the damping of the fundamental mode is obtained for a current density of $\sim 3 \cdot 10^{11}\text{A.m}^{-2}$, in agreement with theoretical predictions. At this critical threshold the MRFM detects a small change of static magnetization, a behavior consistent with the onset of an auto-oscillation regime.Comment: 6 pages 4 figure

Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt

We report on an experimental study on the spin-waves relaxation rate in two series of nanodisks of diameter $\phi=$300, 500 and 700~nm, patterned out of two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance force microscope, we measure precisely the ferromagnetic resonance linewidth of each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth in the nanostructure is sensibly smaller than the one measured in the extended film. Analysis of the frequency dependence of the spectral linewidth indicates that the improvement is principally due to the suppression of the inhomogeneous part of the broadening due to geometrical confinement, suggesting that only the homogeneous broadening contributes to the linewidth of the nanostructure. For the bare YIG nano-disks, the broadening is associated to a damping constant $\alpha = 4 \cdot 10^{-4}$. A 3 fold increase of the linewidth is observed for the series with Pt cap layer, attributed to the spin pumping effect. The measured enhancement allows to extract the spin mixing conductance found to be $G_{\uparrow \downarrow}= 1.55 \cdot 10^{14}~ \Omega^{-1}\text{m}^{-2}$ for our YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the design of YIG based nanostructures with optimized magnetic losses.Comment: 4 pages, 3 figure

Spectrum of the Ap-Laplacian Operator

This work deals with the nonlinear boundary eigenvalue problem(V:P(Gammaho;I)):-A_p u = lambda ho(x)|u|^{p-2}u in I =], b[,u(a) = u(b) = 0,where A_p is called the A_p-Laplacian operator and defined by A_p u = (Gamma(x) |u'|^{p-2}u'),p > 1, lambda is a real parameter, ho is an indefinite weight, a, b are real numbers and Gamma in C^1(I) cap C^0(overline{I}) and it is nonnegative on overline{I}.We prove in this paper that the spectrum of the A_p-Laplacian operator is given by a sequence of eigenvalues. Moreover, each eigenvalue is simple, isolated andverifies the strict monotonicity property with respect to the weight ho and the domain I. The k¡th eigenfunction corresponding to the k-th eigenvalue has exactly k-1 zeros in (a,b). Finally, we give a simple variational formulation of eigenvalues