Low-temperature Magnetic Measurements Research Articles

Magnetic Nanoparticles in Human Cervical Skin.

Magnetic iron oxide nanoparticles, magnetite/maghemite, have been identified in human tissues, including the brain, meninges, heart, liver, and spleen. As these nanoparticles may play a role in the pathogenesis of neurodegenerative diseases, a pilot study explored the occurrence of these particles in the cervical (neck) skin of 10 patients with Parkinson's disease and 10 healthy controls. Magnetometry and transmission electron microscopy analyses revealed magnetite/maghemite nanoparticles in the skin samples of every study participant. Regarding magnetite/maghemite concentrations of the single-domain particles, no significant between-group difference was emerged. In low-temperature magnetic measurement, a magnetic anomaly at ~50 K was evident mainly in the dermal samples of the Parkinson group. This anomaly was larger than the effect related to the magnetic ordering of molecular oxygen. The temperature range of the anomaly, and the size-range of magnetite/maghemite, both refute the idea of magnetic ordering of any iron phase other than magnetite. We propose that the explanation for the finding is interaction between clusters of superparamagnetic and single-domain-sized nanoparticles. The source and significance of these particles remains speculative.

Decoherence measurements in crystals of molecular magnets

Decoherence processes in crystals of molecular magnets are prototypical for interacting electronic spin systems. We analyze the Landau-Zener dynamics of the archetypical TbPc$_2$ complex diluted in a diamagnetic monocrystal. The dependence of the tunneling probability on the field sweep rate is evaluated in the framework of the recently proposed master equation in which the decoherence processes are described through a phenomenological Lindblad operator. Thus, we showcase low temperature magnetic measurements that complement resonant techniques in determining small tunnel splittings and dephasing times.

Low-Temperature Properties of CePt3P Tuned by Magnetic Field**Supported by the Zhejiang Provincial Natural Science Foundation of China under Grant No LQ19A040006, and the Scientific Research Fund of Zhejiang Provincial Education Department under Grant No Y201840160.

We present low-temperature magnetization, magnetoresistance and specific heat measurements on the Kondo lattice compound CePt3P under applied magnetic fields up to 9.0 T. At zero field, CePt3P exhibits a moderately enhanced Sommerfeld coefficient of electronic specific heat γCe = 86 mJ/mol·K2 as well as two successive magnetic transitions of Ce 4f moments: an antiferromagnetic ordering at TN1 = 3.0K and a spin reorientation at TN2 = 1.9 K. The value of TN1 shifts to lower temperature as magnetic field increases, and it is ultimately suppressed around Bc ∼ 3.0T at 1.5 K. No evidence of non-Fermi liquid behavior is observed around Bc down to the lowest temperature measured. Moreover, γ decreases monotonously with increasing the magnetic field. On the other hand, the electrical resistivity shows an anomalous temperature dependence ρ ∝ Tn with the exponent n decreasing monotonously from ∼2.6 around Bc down to ∼1.7 for B = 9.0 T. The T–B phase diagram constructed from the present experimental results of CePt3P does not match the quantum criticality scenario of heavy fermion systems.

Electronic Communication between S=1/2 Spins in Negatively-charged Double-caged Fullerene C60 Derivative Bonded by Two Single Bonds and Pyrrolizidine Bridge.

Radical anion salt {cryptand[2.2.2] (K+ )}2 (bispheroid)2- ⋅3.5C6 H4 Cl2 (1) of the double-caged fullerene C60 derivative, in which fullerene cages are linked by a cyclobutane bridging cycle and additionally by a pyrrolizidine moiety, was obtained. Each fullerene cage in this derivative accepts one electron on reduction, thus forming the (bispheroid)2- dianions with two interacting S=1/2 spins on the neighboring cages. Low-temperature magnetic measurements reveal a singlet ground state of the bispheroid dianions whereas triplet contributions prevail at increased temperature. An estimated exchange interaction between two spins J/kB =-78 K in 1 indicates strong magnetic coupling between them, nearly two times higher than that (J/kB =-44.7 K) in previously studied (C60 - )2 dimers linked via a cyclobutane bridge only. The enhancement of magnetic coupling in 1 can be explained by a shorter distance between the fullerene cages and, possibly, an additional channel for the magnetic exchange provided by a pyrrolizidine bridge. Quantum-chemical calculations of the lowest electronic state of the dianions by means of multi-configuration quasi-degenerate perturbation theory support the experimental findings.

Magnetic-field-induced incommensurate to collinear spin order transition in NiBr2

The triangular spin lattice of NiBr2 is a canonical example of the frustrated helimagnet that shows a collinear commensurate antiferromagnetic to an incommensurate spin helix phase transition on cooling. Herein, we have studied a self-flux grown NiBr2 single crystal by neutron diffraction and low temperature magnetization measurements at fields up to 14 T. Experimental findings enable the deduction of the driving force responsible for the spin spiral ordering. The neutron diffraction data reveal satellite peaks representing characteristic features of an incommensurate magnetic state. The satellites develop symmetrically below TN=44.0(1)K, replacing the main magnetic reflections. Interestingly, a field-induced incommensurate to commensurate spin phase transition has been successfully demonstrated, which enforces the spin helix to restore the high temperature compensated antiferromagnetic structure. This reorientation can be described by a spin-flop in the (a–b) basal plane of a triangular spin lattice system. The findings offer a novel way for spin helix control of incommensurate phases, having immense scientific and technological implications in the next-generation data storage devices.

The effects of dislocations on crystallographic twins and domain wall motion in magnetite at the Verwey transition

Pure magnetite experiences a first-order phase transition (the Verwey transition) near 120–125 K wherein the mineral’s symmetry changes from cubic to monoclinic. This transformation results in the formation of fine-scale crystallographic twins and is accompanied by a profound change in magnetic properties. The Verwey transition is critical to a variety of applications in environmental magnetism and paleomagnetism because its expression is diagnostic for the presence of stoichiometric (or nearly stoichiometric) magnetite and cycling through the Verwey transition tends to remove the majority of multidomain magnetic remanence. Internal and external stresses demonstrably affect the onset of the Verwey transition. Dislocations create localized internal stress fields and have been cited as a possible source of an altered Verwey transition in deformed samples. To further investigate this behavior, a laboratory-deformed magnetite sample was examined inside a transmission electron microscope as it was cooled through the Verwey transition. Operating the microscope in the Fresnel mode of Lorentz microscopy enabled imaging of the interactions between dislocations, magnetic domain walls, and low-temperature crystallographic twin formation during the phase transition. To relate the observed changes to more readily measurable bulk sample magnetic behavior, low-temperature magnetic measurements were also taken using SQUID magnetometry. This study allows us, for the first time, to observe the Verwey transition in a defect-rich area. Dislocations, and their associated stress fields, impede the development of monoclinic magnetite twin structures during the phase transition and increase the remanence of a magnetite sample after cooling and warming through the Verwey transition.

Synthesis, structure and magnetic properties of copper(ii) azide.

A novel azide-bridged copper compound without an auxiliary ligand has been synthesized and characterized by single-crystal diffraction analysis. The compound consists of 1D double chains with end-on (EO) azide bridges. Furthermore, the neighboring chains are connected by weak coordination bonds, which leads to the formation of a 3D architecture. Low-temperature magnetic measurements reveal that antiferromagnetic interactions are dominant, with concomitant spin-canted antiferromagnetism.

Low-Temperature Magnetization Measurements with Precise Two-Axis Alignment of the Sample Orientation

We present an experimental method of low-temperature magnetization measurements with a two-axis alignment of the sample orientation. An in situ alignment of the sample is performed within an accura...

Low temperature studies of Bi doped Pr0.6Sr0.4MnO3 manganites: magnetization and magneto-transport

Low temperature magnetization and resistivity measurements of bismuth (Bi) doped Pr0.6− xBixSr0.4MnO3 (x = 0.2, 0.23 and 0.25) manganites synthesized by solid state reaction method are reported here. Resistivity measurements in all bismuth doped samples in the absence of field show no significant metal–insulator transition. But for x = 0.2, in zero field the transition observed at lower temperature is associated with hysteresis indicating its first order nature. The resistivity and magnetization measurements establish the coexistence of ferromagnetic metallic and antiferromagnetic insulating phase at lower temperature. We present magnetization and resistivity measurements on higher concentration of bismuth exhibiting the coexistence of two phases at low temperature and the kinetic arrest of a first-order ferromagnetic-to-antiferromagnetic transition

Study of Structural, Magnetic and Optical Properties of $$\hbox {BiFeO}_{3}{-}\hbox {PbTiO}_{3}$$ BiFeO 3 - PbTiO 3 Multiferroic Composites

The crystalline samples of lead titanate altered bismuth ferrite ( $$\hbox {BiFeO}_{3})_{1-{x}}(\hbox {PbTiO}_{3})_{{x}}$$ [ $$x= 0, 0.1, 0.2, 0.3, 0.4$$ and 0.5] have been synthesized by high-temperature solid-state reaction technique. The formation of the materials was affirmed through fundamental investigation utilizing X-ray diffraction which uncovers the presence of morphotropic phase boundary (MPB) in composite. XRD examination displays structural change from rhombohedral ( $$x=0.0$$ ) to tetragonal ( $$x=0.4$$ ). Estimated grain size along (104) peak was observed to be diminished with the increase in content of $$\hbox {PbTiO}_{3}$$ due to mixing of tetragonal phases. SEM and EDAX of sample were carried out for analysis of surface morphology and verification of chemical homogeneity, respectively. Study of M-H graph reveals antiferromagnetic nature of $$\hbox {BiFeO}_{3}$$ . Magnetic measurement of ( $$\hbox {BiFeO}_{3})_{1-{x}}(\hbox {PbTiO}_{3})_{{x}}$$ ceramics shows weak-induced ferromagnetism by substituent effects at temperature of 5 K. Low-temperature magnetic measurement under ZFC reveals an anomaly in tetragonal phase of MPB for composition $$x=0.2$$ and 0.3. With respect to $$\hbox {BiFeO}_{3}$$ , $$\hbox {BiFeO}_{3}{-}\hbox {PbTiO}_{3}$$ ceramics displays advancement in the electric polarization. Direct and indirect band gaps are modified with variation of $$\hbox {PbTiO}_{3}$$ in $$\hbox {BiFeO}_{3}{-}\hbox {PbTiO}_{3}$$ composites.

Scandium plumbides Sc2Ni2Pb, ScNi1.34Pb and ScCuPb

The crystal structures of three new Sc-based plumbides have been determined from the single-crystal X-ray diffraction data. Sc2Ni2Pb crystallizes with an orthorhombic structure of the Mn2AlB2 - type (space group Cmmm, No. 65, lattice parameters: а = 3.96386(18), b = 13.5551(6), с = 3.35576(11) Å, Z = 2, R1 = 0.0102, wR2 = 0.0249). ScNi1.34Pb forms with a cubic unit cell of the MnCu2Al - type (space group Fm-3m, No. 225, lattice parameter а = 6.25096(12) Å, Z = 4, R1 = 0.0066, wR2 = 0.0141). ScCuPb crystallizes with the hexagonal LiGaGe - type structure (space group P63mc, No. 186, lattice parameters: а = 4.4338(2), с = 6.9500(4) Å, Z = 2, R1 = 0.0383, wR2 = 0.0920). Low-temperature magnetic measurements have revealed that the compound Sc2Ni2Pb is a Pauli paramagnet with the molar magnetic susceptibility of about 2.4 × 10−4 emu/mole.

Effect of calcinations on the structural and magnetic properties of magnesium ferrite nanoparticles prepared by sol gel method

Magnesium ferrite nanoparticles calcined at 300 °C, 350 °C, 400 °C, 450 °C were synthesized by sol-gel method. The effects of calcinations on the cation distribution, structural and magnetic properties have been investigated. X-ray diffraction (XRD) and vibrating scanning magnetometer (VSM) were used to characterize the structural and magnetic properties. X-ray diffraction analysis revealed the formation of single phase MgFe2O4 in all the samples. Lattice constant and crystallite size increased with calcination. X-ray diffraction data were used to estimate the average cationic distribution among A site and B site. Cationic distribution shows that there is migration of cation between tetrahedral A site and octahedral B site. Saturation magnetization increased with particle size. Coercivity decreased with calcination temperature as a result of decrease in pinning effect at the grain boundary. Curie temperature (TC) decreased slightly due to weakening of A-B exchange interaction. Low temperature magnetic measurement revealed that blocking temperature (TB) increased due to strong magnetic interaction.

Synthesis and low temperature magnetic measurements of polycrystalline Gadolinium nanowires

Highly ordered and reproducible Gd nanowires have been reported via DC electrodeposition method. In this regard, templates with different diameters 100 nm, 50 nm and 20 nm were utilized. Shape morphology, reproducibly and homogeneity of nanowires were investigated with field emission scanning electron microscopy (FE-SEM). Morphological analyses confirm as required diameter, length and aspect ratio. Structurally, body centered cubic (bcc) phase was observed with Rietveld refinement of X-ray diffraction (XRD) patterns for all diameters. Magnetic investigations are including zero field cooled (ZFC) and field cooled (FC) and hysteresis measurement by using physical property measurement system (PPMS). These magnetic analyses of nanowires embedded in AAO templates predict mix phase with superparamagnetic and ferromagnetic clusters.

Bound magnetic polaron driven room-temperature ferromagnetism in Ni doped ZnS nanoparticles

Magnetism in dilute magnetic semiconductors (DMSs) has been a controversial topic since its discovery. There are many models which predict the origin of room temperature ferromagnetism (RTFM) in TM doped wide band gap semiconductors. Here, we report RTFM in chemically synthesized cubic Zn1-xNixS (0 ≤ x ≤ 0.08) DMS nanoparticles of ∼3–5 nm size. Ferromagnetic behavior (at 300 K and 5 K) was found to increase with the increase in Ni doping concentration and was understood due to defect induced ferromagnetism. The low temperature magnetization measurement (ZFC-FC) shows that the nanoparticles are strongly coupled by magnetic interactions. Optical studies showed decrease in the energy bandgap along with the presence of sulfur and zinc vacancies and surface defects. Low temperature resistivity measurement depicted the semiconducting nature of the synthesized samples. With increase in doping concentration, an increase in the resistive behavior was observed which was explained in the realm of defects states created due to doping of the Ni ions.

Multiferroic and magneto-dielectric properties in Fe doped BaTiO3

Polycrystalline barium titanate (BTO) samples doped with infinitesimal quantity of iron separately and simultaneously in both A and B sites are prepared using solid state reaction method with an emphasis on its site preference. Structural studies establish the transformation from tetragonal to pseudo-cubic phase upon changing the dopant site. An appreciable compressive lattice strain is induced when Fe is doped in the A-site while it becomes tensile and negligibly small when Fe occupies B-site. Further, the suppression of 308 cm−1 band in the Raman spectra highlights the coexisting cubic and tetragonal phases in A-site doped BTO. Ferroelectric ordering is validated using P–E loop and PUND (positive up and negative down) measurements. Dielectric constant undergoes a transition from ferroelectric to paraelectric state at 388 K for BTO and it varies with occupation site of Fe. Low temperature magnetic measurements reveal the strong antiferromagnetic coupling in A-site doped BTO sample. Magneto-dielectric measurements portray the proper choice of doping site in BaTiO3 so as to introduce multiple magnetic and electric states in it.

Structure and magnetic properties of synthesized fine cerium dioxide nanoparticles

Cerium dioxide, which is diamagnetic in its bulk crystalline fluorite form, exhibits ferromagnetism when prepared as a nanopowder. This characteristic has recently been ascribed to localized electron spin moments formed at oxygen vacancies near the nanoparticle surfaces. In the present study, a number of structure-sensitive and magnetic methods were applied to CeO2 nanopowders prepared from the carbonate precursor by treatment at different calcination temperatures. The low-temperature magnetization measurements subsequently performed via 57Fe Mössbauer spectroscopy revealed the presence of small amounts of iron impurities in the samples as well as in the chemicals used to prepare them. These experimental findings and our theoretical data analysis of iron impurities at the ppm level provide a plausible explanation for the ferromagnetic behaviour of cerium oxide.

Why magnetite is not the only indicator of past rainfall in the Chinese Loess Plateau?

This study investigates the magnetic mineralogy of palaeosol S5 from Xifeng (XF), Linyou (LY) and Baoji (BJ) sections with increasing annual precipitation from north to the south on the Chinese Loess Plateau. Palaeosol S5 samples from these three localities are further prepared as magnetic extracts and separation residues. Low-temperature magnetic measurements including field cooled and zero field cooled (FC/ZFC) remanence, in-phase magnetic susceptibility, thermal remanent magnetization and room temperature saturation isothermal remanence magnetization (RTSIRM), with X-ray diffraction measurements are carried out for all magnetic extracts and separation residues samples. The asymmetric rounded 'hump' in cooling curves on RTSIRM and the 'tilted' Verwey transition on ZFC/FC curves suggest that partially oxidized magnetite is the dominant magnetic contributor, not pure maghemite or magnetite. Furthermore, The Verwey transitions on cooling curves slightly decrease and the increased slope of 'tilted' Verwey transition on ZFC remanence curves show that the degree of oxidation of magnetite between localities increases in the order XF-LY-BJ. Hard isothermal remanent magnetization, X-ray diffraction data and the difference of magnetization inwarming curves of RTSIRM suggest that both hematite concentration in magnetic extracts and goethite concentration in separation residues increase from XF to BJ. Frequency-dependent susceptibility and ZFC/FC curves show that BJS5 layer formed under high palaeoprecipitation has less superparamagnetic (SP) but more single domain to pseudo-single domain particles, because SP maghemite was dissolved and transformed into goethite by temporary waterlogging. The increase in hematite concentration is interpreted as due to SP maghemite oxidation or original goethite dehydration within dry soil environment. Therefore, transformation of maghemite to goethite in waterlogged phases of the S5 palaeosol led to the loss of magnetization.

Electrochemical and in-situ X-ray diffraction studies of LiMn1.5Ni0.5O4 particles synthesized using two-step preparation

High-voltage cathode LiMn1.5Ni0.5O4 particles with average size of approximately 2 μm were prepared using a two-step process. Low-temperature magnetic measurements indicated them as ferrimagnetic materials with high Neel temperature (146.5 K) and high magnetization (107 emu/g at 4.5 K) that closely approximates the theoretical value of the stoichiometric LiMn1.5Ni0.5O4 compound. Because of their high-purity and high crystallinity, their redox signals were observed only around 4.7 V. Their low-rate capacity was sufficiently high (about 140 mAh/g at 0.1 C). Their capacity retention after the 100th cycle was higher than 95%. In spite of the low specific surface area of the LiMn1.5Ni0.5O4 particles, they exhibited high reversible capacity even at a high-current rate. Additionally, the in-situ X-ray diffraction was conducted to elucidate the reaction process, which indicated that the electrochemical reaction progresses reversibly with two consecutive two-phase reactions. The lattice parameters of three corresponding phases remained almost unchanged on the reactions (0.8165, 0.8087, and 0.8000 nm). The presence of the intermediate phase might give the relaxation of the structural variation during the electrochemical reaction.

Synthesis and Characterisation of Superparamagnetic MgFe2O4 Nanoferrite

Nanocrystalline MgFe2O4 with crystallite size of 10.4 nm was synthesised using combustion method and characterised for structural, electrical, and magnetic properties. The powder X-ray diffraction analysis reveals the single-phase nature of MgFe2O4. The field emission scanning electron microscopy image shows the nanosized grains. The magnetic study reveals the superparamagnetic behaviour of MgFe2O4 with saturation magnetisation value of 14.57 emu/g. The blocking temperature is determined using low-temperature magnetic measurement which is equal to 139 K. Electrical study shows that the value of AC conductivity at 1 Hz is 1.12 × 10− 8 S/cm at 303 K and increases with frequency as well as temperature. The complex impedance analysis shows the grain and grain boundary resistance equal to 6.23 × 106 Ω and 1.27 × 107 Ω, respectively. The complex electric modulus analysis confirms the presence of two relaxation processes in nanocrystalline MgFe2O4.

Application of SQUIDs to low temperature and high magnetic field measurements-Ultra low noise torque magnetometry.

Torque magnetometry is a key method to measure the magnetic anisotropy and quantum oscillations in metals. In order to resolve quantum oscillations in sub-millimeter sized samples, piezo-electric micro-cantilevers were introduced. In the case of strongly correlated metals with large Fermi surfaces and high cyclotron masses, magnetic torque resolving powers in excess of 104 are required at temperatures well below 1 K and magnetic fields beyond 10 T. Here, we present a new broadband read-out scheme for piezo-electric micro-cantilevers via Wheatstone-type resistance measurements in magnetic fields up to 15 T and temperatures down to 200 mK. By using a two-stage superconducting-quantum interference device as a null detector of a cold Wheatstone bridge, we were able to achieve a magnetic moment resolution of Δm = 4 × 10-15 J/T at maximal field and 700 mK, outperforming conventional magnetometers by at least one order of magnitude in this temperature and magnetic field range. Exemplary de Haas-van Alphen measurement of a newly grown delafossite, PdRhO2, was used to show the superior performance of our setup.