Field Dependence Of Ac Susceptibility Research Articles

Emergence of field-induced memory effect in spin ices

Out-of-equilibrium investigation of strongly correlated materials deciphers the hidden equilibrium properties. Herein, we have investigated the out-of-equilibrium magnetic properties of polycrystalline Dy2Ti2O7 and Ho2Ti2O7 spin ices. Our experimental findings reveal the emergence of magnetic field-induced anomalous hysteresis observed solely in temperature-and magnetic field-dependent AC susceptibility measurements. The observed memory effect (anomalous thermomagnetic hysteresis) exhibits a strong dependence on both thermal and non-thermal driving variables. Owing to the non-collinear spin structure, the applied DC bias magnetic field produces quenched disorder sites in the cooperative Ising spin matrix and suppresses the spin–phonon coupling. These quench disorders create a dynamic spin correlation, having slow spin relaxation and quick decay time, which additionally contribute to AC susceptibility. The initial conditions and measurement protocol decide the magnitude and sign of this dynamical term contributing to AC susceptibility. It is being suggested that such out-of-equilibrium properties arise from the combined influences of geometric frustration, disorder, and the cooperative nature of spin dynamics exhibited by these materials.

Canonical Spin Glass and the Anomalous Hall Effect in a Centrosymmetric Ferrimagnet.

Centrosymmetric ferro/ferrimagnets provide an ideal arena for fundamental research due to their fascinating magnetic and structural characters. In this work, the Co0.8MnSn compound with a single hexagonal phase was successfully synthesized, and the magnetic phase transition and magnetic and electronic properties have been systematically investigated. Interestingly, Arrott plots and normalized magnetic entropy changes derived from the isothermal magnetizing curves may imply the first-order nature of the magnetic ordering transition around TC ∼ 121 K. The AC susceptibility analysis and detailed nonequilibrium dynamical studies (including magnetic aging, rejuvenation, and memory effects) reveal the canonical spin-glass state of Co0.8MnSn at lower temperature. Further, negative magnetoresistance and the anomalous Hall effect dominated by a commonly intrinsic term are obtained. Moreover, the field-dependent AC susceptibility data indicated that complicated and nontrivial magnetic spin textures should exist in the compound. These studies may open up further research opportunities in exploring emergent physical phenomena and potential applications in centrosymmetric magnets.

Reentrant double glassy states and simultaneous presence of short- and long-range ordering in metamagnetic Co-doped Bi0·5La0·5Fe0·5Mn0·5O3 multiferroic

A study of the structural and magnetic properties of Bi0·5La0·5Fe0·45Co0·05Mn0·5O3 is presented in the article. We report the rare observations of two glassy transitions below the long-range ordering temperature along with the metamagnetic transitions at low temperatures. Frequency and DC field dependence of AC susceptibility and isothermal relaxation of remnant magnetization studies have all shown the slow spin dynamics for the compound. Interestingly, in the glass phase of the materials, metamagnetic transitions of the antiferromagnetic spins were found which indicate the coexistence of the long-range ordered phase along with the short-range ordered glassy phase. The double cluster glass phases can be comprehended, from the relaxations of the spin clusters arising from the competing magnetic interactions present in the system. Moreover, the roles of additional exchange interactions which are brought to the system by Co doping are also considered in explaining the observed double cluster glass transitions.

Entropic topography associated with field-induced quantum criticality in a magnetic insulator DyVO4

Exploration of low temperature phase transitions associated with quantum critical point is one of the most mystifying fields of research which is under intensive focus in recent times. In this work, through comprehensive experimental evidences, we report the possibility of achieving quantum criticality in the neighborhood of a magnetic field-tuned tricritical point separating paramagnetic, antiferromagnetic and metamagnetic phases in a magnetic insulator, DyVO4. Magnetic susceptibility and heat capacity indicate to the presence of a long-range second order antiferromagnetic transition at TN ~ 3.2 K. Field variation of Magnetic susceptibility and heat capacity, along with differential magnetic susceptibility and DC field dependent AC susceptibility gives evidence of the modification of the antiferromagnetic structure below the tricritical point; implying the presence of a field-induced first order metamagnetic transition which persists down to 1.8 K. Further, the magnetic field dependence of the thermodynamic quantity − dM/dT, which is related to magnetic Gruneisen parameter, approaches a minimum, followed by a crossover near 5 kOe to a maximum; along with a hyperbolic divergence in temperature response of dM/dT in the critical field regime. Temperature response of heat capacity at 5 kOe also shows a deviation from the conventional behavior. Entropic topography phase diagram allows tracking of the variation of the entropy, which indicates towards the emergence of the peak at quantum critical point into a V-shaped region at high temperatures. Our studies yield an inimitable phase diagram describing a tricritical point at which the second-order antiferromagnetic phase line terminates followed by a first order line of metamagnetic transition, as the temperature is lowered, leading to metamagnetic quantum critical end point.

Planar triangular S=3/2 magnet AgCrSe2 : Magnetic frustration, short range correlations, and field-tuned anisotropic cycloidal magnetic order

Single crystals of the hexagonal triangular lattice compound AgCrSe2 have been grown by chemical vapor transport. The crystals have been carefully characterized and studied by magnetic susceptibility, magnetization, specific heat, and thermal expansion. In addition, we used Cr-electron spin resonance and neutron diffraction to probe the Cr 3d3 magnetism microscopically. To obtain the electronic density of states, we employed x-ray absorption and resonant photoemission spectroscopy in combination with density functional theory calculations. Our studies evidence an anisotropic magnetic order below TN=32K. Susceptibility data in small fields of about 1 T reveal an antiferromagnetic (AFM) type of order for H⊥c, whereas for H∥c the data are reminiscent of a field-induced ferromagnetic (FM) structure. At low temperatures and for H⊥c, the field-dependent magnetization and AC susceptibility data evidence a metamagnetic transition at H+=5T, which is absent for H∥c. We assign this to a transition from a planar cycloidal spin structure at low fields to a planar fanlike arrangement above H+. A fully ferromagnetically polarized state is obtained above the saturation field of H⊥S=23.7T at 2 K with a magnetization of Ms=2.8μB/Cr. For H∥c, M(H) monotonically increases and saturates at the same Ms value at H∥S=25.1T at 4.2 K. Above TN, the magnetic susceptibility and specific heat indicate signatures of two dimensional (2D) frustration related to the presence of planar ferromagnetic and antiferromagnetic exchange interactions. We found a pronounced nearly isotropic maximum in both properties at about T*=45K, which is a clear fingerprint of short range correlations and emergent spin fluctuations. Calculations based on a planar 2D Heisenberg model support our experimental findings and suggest a predominant FM exchange among nearest and AFM exchange among third-nearest neighbors. Only a minor contribution might be assigned to the antisymmetric Dzyaloshinskii-Moriya interaction possibly related to the noncentrosymmetric polar space group R3m. Due to these competing interactions, the magnetism in AgCrSe2, in contrast to the oxygen-based delafossites, can be tuned by relatively small, experimentally accessible magnetic fields, allowing us to establish the complete anisotropic magnetic H-T phase diagram in detail.9 MoreReceived 4 August 2021Revised 3 September 2021Accepted 20 September 2021DOI:https://doi.org/10.1103/PhysRevB.104.134410Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFrustrated magnetismMagnetic susceptibilityThermal expansionTechniquesElectron spin resonanceNeutron diffractionPhotoemission spectroscopySpecific heat measurementsCondensed Matter & Materials Physics

Low-field induced topological Hall effect in chiral cubic Cr0.82Mn0.18Ge alloy

The topological Hall effect (THE) in general arises from the Berry phase acquired by conduction electrons moving in a noncoplanar spin textures such as skyrmions. In this paper, low-field induced THE is realized in a chiral-lattice B20-ordered Cr0.82Mn0.18Ge alloy. The maximum topological Hall resistivity of ρxyT ≈ −0.048 μΩ cm at T = 10 K is achieved under a low magnetic field of about μ0H = 0.04 T, which reaches up to ~20% of the anomalous Hall effect. Dip/peak anomalies are observed in the field dependence of AC-susceptibility, which indicates the field evolution of the topologically protected nontrivial spin textures. The results manifest that the Cr0.82Mn0.18Ge alloy should host skyrmions and pave the way for searching new skyrmions materials.

Exotic magnetic behaviour and evidence of cluster glass and Griffiths like phase in Heusler alloys Fe2-xMnxCrAl (0\u2009\u2264\u2009x\u2009\u2264\u20091)

We present a detailed study of structural, magnetic and thermodynamic properties of a series of Heusler alloys Fe2-xMnxCrAl (x = 0, 0.25, 0.5, 0.75 and 1). Structural investigation of this series is carried out using high resolution synchrotron X-ray diffraction. Results suggest that with increasing Mn concentration, the L21 structure of Fe2CrAl is destabilized. The DC magnetization results show a decrement in paramagnetic (PM) to ferromagnetic (FM) phase transition temperature (TC) with increasing Mn concentration. From the systematic analysis of magnetic memory effect, heat capacity, time dependent magnetization, and DC field dependent AC susceptibility studies it is observed that, Fe2CrAl exhibits cluster glass(CG)-like transition approximately at 3.9 K (Tf2). The alloys, Fe1.75Mn0.25CrAl and Fe1.5Mn0.5CrAl exhibit double CG-like transitions near Tf1 ~ 22 K, Tf2 ~ 4.2 K and Tf1 ~ 30.4 K, Tf2 ~ 9.5 K respectively, however, in Fe1.25Mn0.75CrAl, a single CG-like transition is noted at Tf2 ~ 11.5 K below TC. Interestingly, FeMnCrAl shows the absence of long ranged magnetic ordering and this alloy undergoes three CG-like transitions at ~22 K (Tf*), 16.6 K (Tf1) and 11 K (Tf2). At high temperatures, a detailed analysis of temperature response of inverse DC susceptibility clearly reveals the observation of Griffiths phase (GP) above 300 K (T*) in Fe2CrAl and this phase persists with Mn concentration with a decrement in T*.

Mictomagnetic full-Heusler nanoprecipitates in (Ti, Zr, Hf)NiFexSn half-Heusler composites

One of the most recent strategies used to enhance the efficiency of certain thermoelectric (TE) materials relies on the interaction of magnetic dopants with charge carriers and lattice vibrations. Understanding the forms of magnetism inherent to the materials is critical for continued TE performance optimization. Accordingly, we herein analyze the low-temperature magnetic properties of a mictomagnetic composite system we previously engineered for improved TE power generation capabilities. The Ti0.25Zr0.25Hf0.50NiFexSn0.975Sb0.025 set of materials features long-range magnetic ordering as a result of an intentional magnetic full-Heusler secondary phase in the half-Heusler composites. Having the highest population density of magnetic nanoprecipitates, the x = 0.05 sample exhibits both superparamagnetic and cluster glass behavior, with blocking temperatures ranging from ≈ 100 to 250 K. We discern the phenomena from the sharp, open DC magnetization loops, the splitting of the zero-field-cooled and field-cooled DC moments, as well as the frequency- and field-dependent AC susceptibility measurement. In the magnetotransport data, we find evidence for the Kondo effect in these dilute magnetic semiconductors, in addition to weak antilocalization in the pure sample that is abated in the magnetic samples.

Surface effects and spin glass state in Co3O4 coated MnFe2O4 nanoparticles

Surface effects and spin glass state have been studied in Co3O4 coated manganese ferrite (MnFe2O4) nanoparticles by using AC and DC magnetic measurements. Average crystallite size of Co3O4 coated MnFe2O4 nanoparticles was 7 nm as calculated by Debye–Scherrer’s formula. Simulated ZFC/FC revealed higher value of effective anisotropy (Keff) = 5 × 106 erg cm−3 of these nanoparticles as compared to bulk MnFe2O4 due to enhanced surface effects. Temperature dependent saturation magnetization followed the Bloch’s law. Temperature dependent coercivity showed sharp increase below 25 K due to strong surface anisotropy and exchange coupling at interface between ferrimagnetic core and antiferromagnetic surface. For frequency dependent AC-susceptibility, dynamic scaling law fit confirmed the spin glass behavior in Co3O4 coated MnFe2O4 nanoparticles. DC field dependent AC-susceptibility showed the suppression of energy barrier, reduced activation energy and decreased strength of interparticle interactions with increasing DC field. Slow spin relaxation in ZFC protocol further confirmed the presence of spin-glass behavior. All this analysis confirmed the existence of spin-glass behavior as attributed to disordered surface spins and interparticle interactions in these nanoparticles, which gets suppressed after the application of moderate DC field.

Comparison between critical current density in thin superconducting films estimated from temperature and field dependence of ac susceptibility

We have measured an ac magnetic susceptibility of recent second generation high temperature superconductor wires (coated conductor tapes) both as a function of an amplitude of an applied ac magnetic field at fixed temperatures and as a function of temperature at the fixed amplitudes. We find that data acquired by both methods are well described by ac susceptibility calculated on the basis of the Clem–Sanchez model to a response of thin superconducting disks in the Bean critical state to an applied perpendicular ac magnetic field. We show how to link the empirical data dependent on the field amplitude or temperature with theoretical data dependent on the ratio between the critical current density and field amplitude. The critical depinning current densities and its temperature dependence found by both methods are in good agreement. We discuss and compare accuracy and time saving of both methods.

Determination of the magnetic anisotropy constant of Cu/Fe/SiO2/Si by a magneto-optical Kerr effect susceptometer

The magneto-optical Kerr effect susceptometry technique is proposed to determine the uniaxial magnetic anisotropy (UMA) constant Ku. The magnetic properties of Cu/Fe/SiO2/Si grown by dc magnetron sputtering were investigated. The in-plane uniaxial magnetic anisotropy was probed by the magneto-optical Kerr effect (MOKE). The value of UMA, Ku = 2.5 ×103 J/m3, was simulated from the field dependence of ac susceptibility along the hard axis according to the Stoner—Wohlfarth (S—W) model, which is consistent with Ku = 2.7 × 103 J/m3 calculated from the magnetic hysteresis loops. Our results show that the magneto-optical Kerr effect susceptometry can be employed to determine the magnetic anisotropy constant owing to its high sensitivity.

Evidence for Stable High-Temperature Ferromagnetism in Fluorine-Treated C60

It is shown by magnetic field dependent ac susceptibility, magnetic force microscopy, and ferromagnetic resonance that exposure of C60 to fluorine at 160°C produces a stable ferromagnetic material with a Curie temperature well above room temperature. The exposure to fluorine is accomplished by decomposing a fluorine-rich polymer, trifluorochloroethylene [F2C–CFCl]n, which has C60 imbedded in it. Based on previous experimental observations and molecular orbital calculations, it is suggested that the ferromagnetism is arising from crystals of C60–F.

Magnetic field driven transition from an antiferromagnetic ground state to a ferrimagnetic state in Rb0.19Ba0.3Mn1.1[Fe(CN)6]·0.48H2O Prussian blue analogue

We report a magnetic field dependent (H) antiferromagnetic (AFM) to ferrimagnetic (FIM) transition in Rb0.19Ba0.3Mn1.1[Fe(CN)6]·0.48H2O Prussian blue analogue. A microscopic understanding of the nature of this field induced AFM to FIM transition is achieved by carrying out a low temperature neutron diffraction study under an external magnetic field. A decrease in Néel temperature and an evolution of a ferrimagnetic phase with an increase in dc magnetic field are evident in dc magnetic field dependent ac susceptibility measurements. With an increase in H, the FIM phase grows at the expense of the AFM phase, and for H > 4 T, the system fully transforms to the FIM phase. A magnetic structure consisting of an antiparallel stacking of ferrimagnetic sheets along crystallographic c-direction is proposed for the FIM phase. Based on the results obtained, a phase diagram describing the evolution of both magnetic phases under external magnetic field is presented.

Spin-glass and cluster ferromagnetism in RuSr2Y1.5Ce0.5Cu2O10 magneto-superconductor synthesized by HPHT

We report structural, DC magnetization, linear and non-linear AC susceptibility for phase pure RuSr2Y1.5Ce0.5Cu2O10 (YRu-1222) magneto-superconductor. The studied compound is synthesized through HPHT (high pressure high temperature: 6GPa, 1400°C) technique at NIMS-Japan. As synthesized YRu-1222, is crystallized in single phase tetragonal structure with space group I4/mmm. DC magnetic susceptibility showed that studied YRu-1222 is a magneto-superconductor with Ru spins magnetic ordering at around 120K and superconductivity in the Cu-O2 planes below ∼40K. The frequency and field dependent AC susceptibility measurements confirmed the spin-glass (SG) behavior with homogenous/non-homogenous ferromagnetic clusters for the studied system. The frequency variation followed the Vogel–Fulcher law with homogeneous/non-homogenous magnetically interacting ferromagnetic clusters embedded in spin-glass (SG) matrix. Detailed linear and non-linear AC susceptibility measurements are carried out to probe the exact magnetic nature of the studied magneto-superconductor YRu-1222.

Signatures of spin-glass freezing in Co/CoO nanospheres and nanodiscs

We present a study of the magnetic properties of Co nanoparticles having a combination of both spherical and disk shapes. The hcp Co nanospheres with an average diameter of 11nm and nanodiscs of dimensions ∼2.5×15nm2 were prepared by thermal decomposition of di-cobalt octacarbonyl in the presence of an amine surfactant. The as-synthesized nanoparticles were oxidized to grow an antiferromagnetic layer. High resolution transmission electron microscopy showed the presence of a ferromagnet/antiferromagnet (Co/CoO) interface with a 2.2-nm thick CoO shell on the spherical nanoparticles and 0.5nm thick on nanodiscs. We report the temperature and field dependent DC magnetization, frequency, field, and temperature dependent AC susceptibility, and the radio frequency transverse susceptibility. A low temperature paramagnetic behavior was observed in the DC magnetization at high fields and is assigned to defects in the CoO shell that are not coupled to the antiferromagnetic lattice. Our results support the existence of a low temperature frozen, disordered magnetic state, characterized by a strong exchange coupling between the structurally disordered, spin-glass CoO shell and Co core.

Effects of Zn on the grain boundary properties of La 2−xSr xCu 1−yZn yO 4 superconductors

The properties of the grain boundaries (GBs) are of significant importance in high- T c cuprates. Most large scale applications of cuprate superconductors involve usage of sintered compounds. The critical current density and the ability to trap high magnetic flux inside the sample depend largely on the quality of the GBs. Zn has the ability to pin vortices but it also degrades superconductivity. In this study we have investigated the effect of Zn impurity on the intergrain coupling properties in high-quality La 2− x Sr x Cu 1− y Zn y O 4 sintered samples with different hole concentrations, p (≡ x), over a wide range of Zn contents ( y) using field-dependent AC susceptibility (ACS) measurements. The ACS results enabled us to determine the superconducting transition temperature T c , and the temperature T gcp , at which the randomly oriented superconducting grains become coupled as a function of hole and disorder contents. We have analyzed the behavior of the GBs from the systematic evolution of the values of T gcp ( p, y), T c ( p, y), and from the contribution to the field-dependent ACS signal coming from the intergrain shielding current. Zn suppresses both T c and T gcp in a similar fashion. The hole content and the carrier localization due to Zn substitution seem to have significant effect on the coupling properties of the GBs. We have discussed the possible implications of these findings in detail in this article.

Structure and magnetic properties of theHo2Ge2O7pyrogermanate

We report the anisotropic magnetic properties of ${\text{Ho}}_{2}{\text{Ge}}_{2}{\text{O}}_{7}$ determined from dc and ac magnetization, specific heat and powder neutron-diffraction experiments. The magnetic lanthanide sublattice, seen in our refinement of the tetragonal pyrogermanate crystal structure, is a right-handed spiral of edge-sharing and corner-sharing triangles; the local Ho-O coordination indicates that the crystal field is anisotropic. Susceptibility and magnetization data indeed show that the magnetism is highly anisotropic, and the magnetic structure has the Ho moments confined to the plane perpendicular to the structural spiral. The ordered moment of ${\text{Ho}}^{3+}$, as determined from refinement of the neutron-diffraction data, is $9.0\text{ }{\ensuremath{\mu}}_{B}$. Magnetic ordering occurs around 1.6 K. Temperature and field dependent ac susceptibility measurements show that this compound displays spin relaxation phenomena analogous to what is seen in the spin ice pyrochlore system ${\text{Ho}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$.

Low temperature specific heat of the single molecule magnet Fe 8

We present low temperature specific heat and ac-susceptibility measurements of Fe 8 powdered sample. Below 1.3 K, super-paramagnetic blocking effects and an excess specific heat contribution are observed. The latter is attributed to a splitting of the ground state doublet in an inhomogeneous local field of hyperfine and dipolar origin. The local field contributions are evident at the resonances observed in the field dependent ac-susceptibility and specific heat below 0.5 K. The low temperature Schottky contribution is in agreement with known crystal field parameters of effective spin Hamiltonians proposed to simulate EPR and inelastic neutron scattering experiments.

Extreme sensitivity of the Griffiths phase to magnetic field in single crystalLa0.73Ba0.27MnO3

Field-dependent ac susceptibility and low field $(<150\phantom{\rule{0.3em}{0ex}}\mathrm{Oe})$ magnetization measurements on single crystal ${\mathrm{La}}_{0.73}{\mathrm{Ba}}_{0.27}\mathrm{Mn}{\mathrm{O}}_{3}$ reveal features consistent with the appearance of a Griffiths phase in the temperature interval between ${T}_{C}=245$ and $345\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Such features, however, are suppressed by fields of only $150\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$, a result consistent with reduced value of the susceptibility ``exponent'' $(y)$ deduced from these data. Comparisons with the behavior of other doped manganites near optimal doping suggest that the proximity of the mean $A$-site radius $⟨{r}_{A}⟩$ to its undistorted value ${r}_{A}^{0}$ might provide an appropriate measure of the tendency of these systems to nucleate a Griffiths phase.

Long-range magnetic ordering of quasi-one-dimensional S=1/2 Heisenberg antiferromagnet Sr 2Cu(PO 4) 2

Magnetic properties of quasi-one-dimensional S = 1 / 2 Heisenberg antiferromagnet Sr 2Cu(PO 4) 2 were investigated by temperature and field dependence of AC susceptibility down to 0.03 K. A sharp peak was observed at T N = 0.085 K on the temperature dependence of AC susceptibility indicating long-range magnetic ordering. Taking into account the exchange constant, J / k B = 143 K (Hamiltonian = J ∑ S i S i + 1 ), the ratio k B T N/ J is 0.06%. Sr 2Cu(PO 4) 2 is, therefore, one of the best one-dimensional Heisenberg antiferromagnet known so far.