Strain relaxation dynamics of multiferroic orthorhombic manganites

Abstract: Resonant ultrasound spectroscopy has been used to characterise strain coupling and relaxation behavior associated with magnetic/magnetoelectric phase transitions in GdMnO3, TbMnO3 and TbMn0.98Fe0.02O3 through their influence on elastic/anelastic properties. Acoustic attenuation ahead of the paramagnetic to colinear-sinusoidal incommensurate antiferromagnetic transition at ∼41 K correlates with anomalies in dielectric properties and is interpreted in terms of Debye-like freezing processes. A loss peak at ∼150 K is related to a steep increase in electrical conductivity with a polaron mechanism. The activation energy, E a, of ≳0.04 eV from a loss peak at ∼80 K is consistent with the existence of a well-defined temperature interval in which the paramagnetic structure is stabilised by local, dynamic correlations of electric and magnetic polarisation that couple with strain and have relaxation times in the vicinity of ∼10−6 s. Comparison with previously published data for Sm0.6Y0.4MnO3 confirms that this pattern may be typical for multiferroic orthorhombic RMnO3 perovskites (R = Gd, Tb, Dy). A frequency-dependent loss peak near 10 K observed for TbMnO3 and TbMn0.98Fe0.02O3, but not for GdMnO3, yielded E a ⩾ ∼0.002 eV and is interpreted as freezing of some magnetoelastic component of the cycloid structure. Small anomalies in elastic properties associated with the incommensurate and cycloidal magnetic transitions confirm results from thermal expansion data that the magnetic order parameters have weak but significant coupling with strain. Even at strain magnitudes of ∼0.1–1‰, polaron-like strain effects are clearly important in defining the development and evolution of magnetoelectric properties in these materials. Strains associated with the cubic–orthorhombic transition due to the combined Jahn–Teller/octahedral tilting transition in the vicinity of 1500 K are 2–3 orders of magnitude greater. It is inevitable that ferroelastic twin walls due to this transition would have significantly different magnetoelectric properties from homogeneous domains due to magnetoelastic coupling with steep strain gradients

MAGNETIC PROPERTIES OF AMORPHOUS Ni-Pd-Si ALLOYS.

La substitution partielle du palladium par des éléments possédant des électrons 3d tels que Fe, Co ou Ni change profondément les propriétés magnétiques de l'alliage amorphe Pd-Si. Nous avons étudié systématiquement la susceptibilité magnétique des alliages amorphes (NixPd100-x)83Si17 en fonction de la température (4,2 < T < 580 K) et de la concentration (5 < x < 50). On discute brièvement de résultats obtenus.The magnetic properties of amorphous Pd - Si alloys are significantly changed by partly substituting the Pd with 3d elements such as Fe, Co and Ni. The low-field magnetic susceptibility of amorphous (NixPd100-x)83Si17 alloys was systematically investigated as a function of temperature (4.2 < T < 580 K) and concentration (5 < x < 50). We briefly discuss the obtained data

Magnetic Properties of Thorium Ferricyanide

The magnetic properties of Th$\text{}_{3}$[Fe(CN)$\text{}_{6}$]·10H$\text{}_{2}$O were investigated. It was shown that this compound is antiferromagnetically ordered in the low temperature region. The observed antiferromagnetic ordering is stable only in the low field

Magnetic Properties of Milled and Thermal Relaxed YBa2\text{}_{2} (Cu1−x\text{}_{1-x}Fex\text{}_{x})3\text{}_{3}Oy\text{}_{y}

The influence of the mechanical milling and subsequent thermal relaxation on magnetic and superconducting behaviour of YBa$\text{}_{2}$(Cu$\text{}_{1-x}$Fe $\text{}_{x}$)$\text{}_{3}$O$\text{}_{y}$ system has been studied. Two methods of heat treatment were used: Set I - slow cooling from 980°C in flowing O$\text{}_{2}$ and Set II - reducing at 770°C in flowing Ar$\text{}_{2}$ followed by reoxidation in flowing O$\text{}_{2}$ below 400°C. The transition to superconductivity, diamagnetic response, critical current density and the effective magnetic moment in the normal state have been estimated. Our measurements indicate that the reducing atmosphere preparation is less detrimental on superconducting properties. The results are discussed in terms of occupancy Cu sites by Fe and redistribution of oxygen atoms

Magnetic Relaxation and Memory Effect in Nickel-Chromium Cyanide Nanoparticles

The low temperature dynamics of a magnetic nanoparticle system $Ni_3[Cr(CN)_6]_2$ with an average nanoparticles size of 4 nm was studied. Using different temperature and field protocols memory phenomena were studied by the DC magnetization and magnetic relaxation measurements of the system at temperatures below $T_m$ = 19 K. Aging experiments show an absence of any waiting time dependence in the magnetization relaxation due to a field change after zero field and field cooling. This observation discriminates the dynamics of the system from the behaviour of a classical spin-glass

1H\text{}^1H NMR on (NixMn1−x)3[Cr(CN)6]2⋅nH2O(Ni_xMn_{1-x})_3[Cr(CN)_6]_2 \cdot nH_2O

We report on $\text{}^1H$ NMR of $(Ni_xMn_{1-x})3[Cr(CN)_6]_2 \cdot 15H_2O$ hexacyanochromates, where x changes from 0 to 1. The decay time constants of the free induction decay signals described by an effective spin-spin relaxation time $T_{2eff}$ obtained from M(t) = $M_0 \text{exp}(t//T_{2eff})$ decrease as the local magnetic moments increase produced by the magnetic transition metal ions at the sites of the resonant $\text{}^1H$ nuclei. The recovery of the magnetization in the spin-lattice relaxation time $(T_1)$ experiments was single-exponential

Effect of Pressure on Magnetic Properties of TM 3 [Cr(CN) 6 ] 2 · nH 2 O Nanoparticles

Effect of pressure on magnetic properties of magnetic nanoparticles, based on Prussian blue analogues, were studied in pressures up to 1.2 GPa. The Mn 3 [Cr(CN) 6 ] 2 · nH 2 O and Ni 3 [Cr(CN) 6 ] 2 · nH 2 O nanoparticles were prepared by reverse micelle technique. Transmission electron microscopy images show nanoparticles with average diameter of about 3.5 nm embedded in an organic matrix. The characteristic X-ray peaks of nanoparticles are more diffused and broader. Systems of nanoparticles behave as systems of interacting magnetic particles. The Curie temperature TC is reduced from T C = 56 K for Ni-Prussian blue analogues to T C = 21 K for Ni-nanoparticles system and from TC = 65 K for Mn-Prussian blue analogues to T C = 38 K for Mn-nanoparticles system. One can explain this reduction of the Curie temperature and of the saturated magnetization µs by dispersion of nanoparticles in an organic matrix i.e. by a dilution effect. Applied pressure leads to a remarkable increase in T C for system of Mn-nanoparticles (∆T C /∆p = +13 K/GPa) and to only slight decrease in T C for system of Ni-nanoparticles (∆T C /∆p = −3 K/GPa). The pressure effect follows behavior of the mother Prussian blue analogues under pressure. The increase in saturated magnetization, attributed to compression of the organic matrix, is very small

Effect of Pressure on Magnetic Properties of (NH3OH)2CoF4(NH_3OH)_2CoF_4 Fluoro-Metal Complex

Effect of pressure on magnetic properties of a bulk fluoro-metal complex $(NH_3OH)_2MF_4$ was studied. Magnetization measurements suggest that a ferromagnetic transition at $T_{C1}$ = 47 K is followed by a ferrimagnetic one at $T_{C2}$ = 3 K. Both transition temperatures are pressure dependent with the pressure coefficients $dT_{C1}$/ dp = - 2.6 K/GPa and $dT_{C2}$/ dp = 0.26 K/GPa. The opposite sign of the coefficients is an additional indication of a different nature (ferromagnetic/antiferromagnetic) of these two transitions. The effect of pressure on low field magnetization and exchange bias phenomena is small but still visible