Field Sweep Research Articles

Precise Calorimetry of Small Metal Samples Using Noise Thermometry

AbstractWe describe a compact calorimeter that opens ultra-low-temperature heat capacity studies of small metal crystals in moderate magnetic fields. The performance is demonstrated on the canonical heavy fermion metal YbRh$$_{2}$$ 2 Si$$_{2}$$ 2 . Thermometry is provided by a fast current sensing noise thermometer. This single thermometer enables us to cover a wide temperature range of interest from 175 µK to 90 mK with temperature-independent relative precision. Temperatures are tied to the international temperature scale with a single-point calibration. A superconducting solenoid surrounding the cell provides the sample field for tuning its properties and operates a superconducting heat switch. Both adiabatic and relaxation calorimetry techniques, as well as magnetic field sweeps, are employed. The design of the calorimeter results in an addendum heat capacity which is negligible for the study reported. The keys to sample and thermometer thermalisation are the lack of dissipation in the temperature measurement and the steps taken to reduce the parasitic heat leak into the cell to the tens of fW level.

Parahydrogen-Induced 13C Hyperpolarizer Using a Flow Guide for Magnetic Field Cycling to Evoke 1H-13C Spin Order Transfer Toward Metabolic MRI.

The pair-wise addition of parahydrogen, the singlet form of molecular hydrogen, to unsaturated precursors evokes the hyperpolarization of two parahydrogen-derived 1H nuclear spins through a process known as parahydrogen-induced polarization (PHIP). Subsequent spin order transfer (SOT) from the 1H to the surrounding 13C nuclear spins via magnetic field cycling (MFC) results in substantial signal enhancement in 13C magnetic resonance imaging (MRI). Here, we report the development of a unique PHIP 13C hyperpolarizer system using a flow guide for MFC. The optimal MFC scheme for 1H to 13C spin order transfer was quantum-chemically simulated using the J-coupling values of 13C-labeled metabolic tracers. The flow guide system was three-dimensionally designed based on the simulated MFC scheme and pre-measured magnetic field distribution in a zero-field chamber. The system efficiently transfers the spin order of hyperpolarized 1H to a particular 13C spin when the parahydrogenated tracer passes through the flow guide at a designated flow rate. The 13C MRI signal is enhanced more than 40,000 times in 13C-labeled pyruvate and fumarate, compared to the thermal equilibrium level at 1.5 T, was achieved for conducting in vivo metabolic MRI of mice. A fully automated PHIP-based 13C polarizer was developed using a unique flow guide to conduct the MFC for 1H to 13C SOT. The PHIP hyperpolarizer with a flow guide can conduct efficient 1H-13C SOT without a MFC magnetic field sweep system and offers a cost-effective alternative to conventional dynamic nuclear polarization.

Short Didysprosium Covalent Bond Enables High Magnetization Blocking Temperature of a Direct 4f-4f Coupled Dinuclear Single-Molecule Magnet.

Coupling two magnetic anisotropic lanthanide ions via a direct covalent bond is an effective way to realize high magnetization blocking temperature of single-molecule magnets (SMMs) by suppressing quantum tunneling of magnetization (QTM), whereas so far only single-electron lanthanide-lanthanide bonds with relatively large bond distances are stabilized in which coupling between lanthanide and the single electron dominates over weak direct 4f-4f coupling. Herein, we report for the first time synthesis of short Dy(II)-Dy(II) single bond (3.61 Å) confined inside a carbon cage in the form of an endohedral metallofullerene Dy2@C82. Such a direct Dy(II)-Dy(II) covalent bond renders a strong Dy-Dy antiferromagnetic coupling that effectively quenches QTM at zero magnetic field, thus opening up magnetic hysteresis up to 25 K using a field sweep rate of 25 Oe/s, concomitant with a high 100 s magnetization blocking temperature (TB,100s) of 27.2 K.

Room temperature chirality switching and detection in a helimagnetic MnAu2 thin film

Helimagnetic structures, in which the magnetic moments are spirally ordered, host an internal degree of freedom called chirality corresponding to the handedness of the helix. The chirality seems quite robust against disturbances and is therefore promising for next-generation magnetic memory. While the chirality control was recently achieved by the magnetic field sweep with the application of an electric current at low temperature in a conducting helimagnet, problems such as low working temperature and cumbersome control and detection methods have to be solved in practical applications. Here we show chirality switching by electric current pulses at room temperature in a thin-film MnAu2 helimagnetic conductor. Moreover, we have succeeded in detecting the chirality at zero magnetic fields by means of simple transverse resistance measurement utilizing the spin Berry phase in a bilayer device composed of MnAu2 and a spin Hall material Pt. These results may pave the way to helimagnet-based spintronics.

Shear stiffening and magneto-induced properties of magnetorheological elastomer based on self-healing poly(urethane-urea) matrix

A novel multifunctional composite material, defined as self-healing magnetorheological elastomer (SH-MRE), which exhibits both shear stiffening and magnetorheological effects as well as self-healing ability, is obtained by dispersing carbonyl iron particles in a poly(urethane-urea) matrix. The dynamic shear properties are tested through oscillation frequency and magnetic field sweeps. When shear stress is applied with an excitation frequency of 0.1 Hz to 100 Hz, the storage modulus of the poly(urethane-urea) matrix increases sharply, showing a good shear stiffening effect. In addition to the magnetically dependent mechanical properties with a magnetic flux density of 0–0.894 T, the self-healing efficiency of the isotropic SH-MREs with destructive shear damage after healing can be influenced by the mass fraction of the carbonyl iron particles, the applied magnetic field strength and the support of trace solvents. Based on the experimental results, it is believed that the hydrogen bonds in the dynamic hard domains and the magnetic interaction forces between the carbonyl iron particles induced by the magnetic field are the cause of the good multifunctional properties.

The CW-EPR Capabilities of a Dual DNP/EPR Spectrometer Operating at 14 and 7 T

High-field electron paramagnetic resonance (EPR) measurements are indispensable for a better understanding of dynamic nuclear polarization (DNP), which relies on polarization transfer between electron and nuclear spins. DNP experiments are typically performed at high > 7 T magnetic fields and low ≤ 100 K temperatures, while EPR instrumentation capable of EPR measurements under these conditions is scarce. In this paper, we describe the CW EPR capabilities of a dual DNP/EPR spectrometer that is designed to carry out EPR experiments under “DNP conditions” at 14 and 7 T. In the first part, we present the design of this instrument, highlighting the choices made to allow for both DNP and EPR operations. The spectrometer uses a sweepable cryogen-free magnet with NMR-grade homogeneity, a closed-cycle cooling system, a quasi-optical induction mode bridge, and a superheterodyne receiver system. The probe design is optimized for low heat load and fast sample exchange under cryogenic conditions. The spectrometer can operate in frequency and field sweep modes, including wide field sweeps using the main coil of the magnet. In the second part, we present EPR spectra acquired over a wide range of samples and operating conditions, illustrating the CW EPR capabilities of the instrument.

Unveiling the Anomalous Hall Response of the Magnetic Structure Changes in the Epitaxial MnBi2Te4 Films.

Recently discovered as an intrinsic antiferromagnetic topological insulator, MnBi2Te4 has attracted tremendous research interest, as it provides an ideal platform to explore the interplay between topological and magnetic orders. MnBi2Te4 displays distinct exotic topological phases that are inextricably linked to the different magnetic structures of the material. In this study, we conducted electrical transport measurements and systematically investigated the anomalous Hall response of epitaxial MnBi2Te4 films when subjected to an external magnetic field sweep, revealing the different magnetic structures stemming from the interplay of applied fields and the material's intrinsic antiferromagnetic (AFM) ordering. Our results demonstrate that the nonsquare anomalous Hall loop is a consequence of the distinct reversal processes within individual septuple layers. These findings shed light on the intricate magnetic structures in MnBi2Te4 and related materials, offering insights into understanding their transport properties and facilitating the implementation of AFM topological electronics.

Comparison of field sweep and frequency sweep evaluations of Co–Ni ferrite nanoparticles in the short circuit FMR method

Broadband ferromagnetic resonance (BFMR) spectroscopy analysis can be achieved with different setups involving the frequency-sweep and field-sweep setups. To evaluate and compare the two former regimes, a frequency-sweep and a field-sweep shortcut BFMR regimes were conducted on Co–Ni ferrite nanoparticles that were synthesized by the co-precipitation method of metal chlorides. The nanoparticles were structurally and magnetically characterized, with an average particle size of around 23 nm and a spinel structure. The saturation magnetization was about 59 emu/g, and the coercivity was about 30 Oe. The BFMR analyses were achieved through a frequency range of (2–26) GHz and a field range of (0-104)Oe. The two regimes, frequency sweep and field sweep, showed linear behavior between the resonance field and resonance frequency. The frequency–sweep regime displayed more complicated curves involving small multi-peaks within the multi-FMR absorption band that were not found in the field sweep regime. The intercepts of the linear dispersion relationship between the two regimes are nearly equivalent to each other. The field-sweep g-factor was higher and more reasonable than the frequency-sweep one, whereas its damping factor was lower. The fluctuation in the frequency linewidth vs. resonance field in the frequency-sweep method is higher than that for the field-sweep.

Atomic resolution imaging using a novel, compact and stiff scanning tunnelling microscope in cryogen-free superconducting magnet.

We present the design and performance of a novel scanning tunnelling microscope (STM) operating in a cryogen-free superconducting magnet. Our home-built STM head is compact (51.5mm long and 20mm in diameter) and has a single arm that provides complete openness in the scanning area between the tip and sample. The STM head consists of two piezoelectric tubes (PTs), a piezoelectric scanning tube (PST) mounted on a well-polished zirconia shaft, and a large PT housed in a sapphire tube called the motor tube. The main body of the STM head is made of tantalum. In this design, we fixed the sapphire tube to the frame with screws so that the tube's position can be changed quickly. To analyse the stiffness of the STM head unit, we identified the lowest eigenfrequencies with 3 and 4kHz in the bending modes, 8kHz in a torsional mode, and 9kHz in a longitudinal mode by finite element analysis, and also measured the low drift rates in the X-Y plane and in the Z direction. The high performance of the home-built STM was demonstrated by images of the hexagonal graphite lattice at 300 K and in a sweeping magnetic field from 0 T to 9 T. Our results confirm the high stability, vibration resistance, insensitivity to high magnetic fields and the application potential of our newly developed STM for the investigation of low-frequency systems with high static support stiffness in physics, chemistry, material and biological sciences.

Universal Conductance Fluctuations in a MnBi2Te4 Thin Film.

Quantum coherence of electrons can produce striking behaviors in mesoscopic conductors. Although magnetic order can also strongly affect transport, the combination of coherence and magnetic order has been largely unexplored. Here, we examine quantum coherence-driven universal conductance fluctuations in the antiferromagnetic, canted antiferromagnetic, and ferromagnetic phases of a thin film of the topological material MnBi2Te4. In each magnetic phase, we extract a charge carrier phase coherence length of about 100 nm. The conductance magnetofingerprint is repeatable when sweeping applied magnetic field within one magnetic phase. Surprisingly, in the antiferromagnetic and canted antiferromagnetic phases, but not in the ferromagnetic phase, the magnetofingerprint depends on the direction of the field sweep. To explain our observations, we suggest that conductance fluctuation measurements are sensitive to the motion and nucleation of magnetic domain walls in MnBi2Te4.

Effect of light ellipticity and polarization angle on the transient dynamics of the ground-state Hanle effect

We report theoretical investigations on the transient dynamics of the ground-state Hanle effect in the Voigt geometry, where a time-varying scanning magnetic field B (t) is applied perpendicular to the light propagation direction. Transient Hanle signals are calculated for different light polarizations using a theoretical model based on the density matrix approach. First, we study the ellipticity dependence of transient Hanle signals in two configurations in which the major axis of the light polarization ellipse () is aligned either perpendicular or parallel to the field B . For B , elliptical polarization of the light produces oscillations of frequencies 2ΩL(t) and ΩL(t) simultaneously, where ΩL(t) is the Larmor frequency of the corresponding field B (t). On the other hand, in the case of || B , only ΩL(t) oscillation is observed using elliptically polarized light. Second, we vary the tilt angle between the polarization vector of a linearly polarized light and the orientation of the field B and study its effect on the transient response of Hanle signals. Both the amplitude and the decay rate of the oscillations show a strong dependence on the light ellipticity and tilt angle of the polarization vector. In addition, the influence of the magnetic field sweep rate on the transient signals is demonstrated for given values of light ellipticity and polarization angle.

Validation of an in vivo transit dosimetry algorithm using Monte Carlo simulations and ionization chamber measurements.

Transit dosimetry is a safety tool based on the transit images acquired during treatment. Forward-projection transit dosimetry software, as PerFRACTION, compares the transit images acquired with an expected image calculated from the DICOM plan, the CT, and the structure set. This work aims to validate PerFRACTION expected transit dose using PRIMO Monte Carlo simulations and ionization chamber measurements, and propose a methodology based on MPPG5a report. The validation process was divided into three groups of tests according to MPPG5a: basic dose validation, IMRT dose validation, and heterogeneity correction validation. For the basic dose validation, the fields used were the nine fields needed to calibrate PerFRACTION and three jaws-defined. For the IMRT dose validation, seven sweeping gaps fields, the MLC transmission and 29 IMRT fields from 10 breast treatment plans were measured. For the heterogeneity validation, the transit dose of these fields was studied using three phantoms: 10, 30, and a 3cm cork slab placed between 10cm of solid water. The PerFRACTION expected doses were compared with PRIMO Monte Carlo simulation results and ionization chamber measurements. Using the 10cm solid water phantom, for the basic validation fields, the root mean square (RMS) of the difference between PerFRACTION and PRIMO simulations was 0.6%. In the IMRT fields, the RMS of the difference was 1.2%. When comparing respect ionization chamber measurements, the RMS of the difference was 1.0% both for the basic and the IMRT validation. The average passing rate with a γ(2%/2mm, TH=20%) criterion between PRIMO dose distribution and PerFRACTION expected dose was 96.0%±5.8%. We validated PerFRACTION calculated transit dose with PRIMO Monte Carlo and ionization chamber measurements adapting the methodology of the MMPG5a report. The methodology presented can be applied to validate other forward-projection transit dosimetry software.

Landau Diamagnetism and de Haas-van Alphen Oscillations, Formed in Single Crystals of Y3Fe5O12, in Local Nanodimensional-Sized 2D Phase Separation Regions, Located inside Layered Domain Walls at Room Temperature and T = 77 K.

This paper presents results of the magnetic dynamics study (the microwave power absorptions at the fixed frequencies during magnetic field sweeping) in samples of Y3Fe5O12 single crystals in the form of plates and spheres of various sizes, at frequencies exceeding 30 GHz, in magnetic fields up to 18 kOe, at room temperature, and T = 77 K. It was found that in this case, the inhomogeneity's of the magnetic state manifested itself in the Y3Fe5O12 samples as 2D local phase separation regions. Such 2D phase separation regions formed inside layered domain walls representing superlattices with sizes of 700-900 Å. Depending on the shape and size of the studied plates and spheres, Landau diamagnetism or de Haas-van Alphen oscillations were observed in the 2D phase separation regions at room temperature and T = 77 K.

The nature of the frequency dependence of the adiabatic temperature change in Ni50Mn28Ga22-x(Cu, Zn)x Heusler alloys in cyclic magnetic fields

This study presents the results of direct measurements of the adiabatic temperature change (∆Tad) in Ni50Mn28Ga22−x(Cu, Zn)x (x = 0; 1,5) alloys in cyclic magnetic fields of 0.62 and 1.2 T at frequencies f= 1, 5, 10, and 20 Hz. The substitution of zinc and copper for the initial composition resulted in a decrease in ∆Tad and a stronger frequency dependence. The strong frequency dependence of ∆Tad near TC in the Ni50Mn28Ga22−x(Cu, Zn)x system is due to the inhomogeneous microstructure and the coexistence of martensite-austenite phases, which give rise to two simultaneously acting mechanisms. Firstly, the addition of Zn and Cu increases the coercive force HC, resulting in an increase in the viscosity coefficient. Secondly, an increase in the frequency of the cyclic magnetic field (i.e., an increase in the field sweep rate) leads to the same effect, increasing the viscosity coefficient. Which, in our opinion, is the reason for the frequency dependences of ∆Tad near TC. The study found that the specific cooling power (SCP) for the Ni50Mn28Ga22 sample in a cyclic magnetic field of 1.2 T increased with frequency, reaching 4.75 W/g at 20 Hz, which is 14.1 times greater than at 1 Hz. This suggests that, under conditions of sufficient heat exchange, the cooling efficiency of a magnetic refrigerator can be greatly improved by increasing the operating frequency.

The Landau–Zener–Stückelberg–Majorana transition in the T2 ≪ T1 limit

Landau–Zener–Stückelberg–Majorana (LZSM) transitions occur between quantum states when parameters in the system’s Hamiltonian are varied continuously and rapidly. In magnetic resonance, losses in adiabatic rapid passage can be understood using the physics of LZSM transitions. Most treatments of LZSM transitions ignore the T2 dephasing of coherences, however. Motivated by ongoing work in magnetic resonance force microscopy, we employ the Bloch equations, coordinate transformation, and the Magnus expansion to derive expressions for the final magnetization following a rapid field sweep at fixed irradiation intensity that include T2 losses. Our derivation introduces an inversion-function, Fourier transform method for numerically evaluating highly oscillatory integrals. Expressions for the final magnetization are given for low and high irradiation intensity, valid in the T2≪T1 limit. Analytical results are compared to numerical simulations and nuclear magnetic resonance experiments. Our relatively straightforward calculation reproduces semiquantitatively the well known LZSM result in the T2→0 limit.

Hysteretic magnetoresistance in superconducting SrTiO3/LaAlO3/SrTiO3 trilayer interface system

We investigated the electrical transport properties of the SrTiO3/LaAlO3/SrTiO3 (STO/LAO/STO) trilayer interface system. We found that the trilayer exhibits superconductivity at temperatures below 0.2 K. In the superconducting regime, the magnetoresistance (MR) of the system shows pronounced hysteresis, possibly due to the interplay of ferromagnetism and superconductivity. The magnitude of MR hysteresis strongly depends on the magnetic field sweep rate, and we observed a threshold field-sweep rate below which no MR is detected. At high sweep rates, the MR exhibits superconducting-normal-superconducting transition behavior. To explain these observations, we propose a model based on the ohmic heating from superconducting phase slip centers beneath Bloch-type magnetic domain walls in the ferromagnetic layer. Furthermore, we observed complex features in the MR curves that are likely due to domain wall motion in the system.

Nonreciprocal transmission of magnetoacoustic waves in compensated synthetic antiferromagnets

We investigate the interaction between surface acoustic waves (SAWs) and spin waves (SWs) in a Pt/Co($2\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$)/Ru($0.85\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$)/Co($2\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$)/Pt compensated synthetic antiferromagnet (SAF) composed of two ferromagnetic layers with equal thicknesses separated by a thin nonmagnetic Ru spacer layer. Because of the combined presence of interlayer dipolar coupling fields and interfacial Dzyaloshinskii--Moriya interaction (iDMI), the optical SW mode shows a large nondegenerate dispersion relation for counter-propagating SWs. Due to resonant SAW-SW interaction, we observe a nonreciprocal SAW transmission in the prepared piezoelectric/SAF hybrid device. We demonstrate that the nonreciprocity of the SAW transmission in symmetric SAFs with equal thicknesses of the magnetic layers can show a substantially different characteristic behavior in comparison to asymmetric SAFs or magnetic single layers with iDMI. For the prepared SAF, the nonreciprocal shift of the magnetoacoustic resonance fields and the magnetoacoustic SW excitation efficiency depend on the external magnetic field sweep direction. For one magnetic field sweep direction and angle of the magnetic field, the resonance fields of the waves propagating in one direction are larger than for the waves propagating in the opposite direction. In addition, the magnitude of the nonreciprocal field shift is at minimum if the external magnetic field is aligned perpendicular to the SW propagation direction. The experimental results are in agreement with a phenomenological SAW-SW interaction model.

Demonstration of geometric diabatic control of quantum states

Geometric effects can play a pivotal role in streamlining quantum manipulation. We demonstrate a geometric diabatic control, that is, perfect tunneling between spin states in a diamond by a quadratic sweep of a driving field. The field sweep speed for the perfect tunneling is determined by the geometric amplitude factor and can be tuned arbitrarily. Our results are obtained by testing a quadratic version of Berry's twisted Landau-Zener model. This geometric tuning is robust over a wide parameter range. Our work provides a basis for quantum control in various systems, including condensed-matter physics, quantum computation, and nuclear magnetic resonance.

ABWI AIRBORNE BINOCULAR WHISKBROOM IMAGER: CAMERA PRINCIPLES AND THE WORKFLOW

Abstract. The common imaging methods of airborne cameras are linear array pushbroom and area-array interval exposure, and the sensors or lens of them cannot be rotated. With the development of oblique photogrammetry and UAV mapping, there are new advances in airborne whiskbroom sensors. Because of their unique imaging method, they can obtain the side texture information of features more efficiently. ABWI is a new generation of airborne sweeping sensors with the dual-view area-array whiskbroom imaging method. It has a maximum sweeping field of view of 120° and can also acquire spectral information in four bands (RGB and NIR) at the radiometric resolution of 12 bits. Additionally, the camera system is equipped with a laser ranger to assist with other measurement purposes. This paper introduces the camera structure, imaging principle and corresponding data processing workflow of ABWI, and summarizes its advantages and new application scenarios.

Quantitative estimation of coercive field in a ferromagnetic grain using field sweep simulation

High coercivity is an important property of permanent magnets for application in energy conversion devices. The Nd magnet, ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$, is a typical material. Because coercivity is a long-time relaxation phenomenon, which originates from a strong metastable magnetic state, it is difficult to estimate coercive field (coercive force) studying the time evolution dynamics simulation of a model with atomistic parameters under the limitation of the simulation time. In our recent study [M. Nishino et al., Phys. Rev. B 102, 020413(R) (2020)], we presented a method to estimate coercivity using a statistical method to extend the limitation of simulation time and evaluated appropriately the coercive field of a single grain of the Nd magnet. In the present study, we propose an alternative method to estimate coercivity more conveniently using the field-dependent survival (nonreversal) probability generated by a time evolution simulation under a field sweep. We demonstrate that the coercive field of the single grain can be estimated. In this method, not only coercive field but also the zero-field energy barrier and field for the zero-energy barrier can be estimated. We discuss detailed features of the estimation of these quantities.