We report the effect of Ga substitution on magnetization, magnetoresistance, and magnetostriction in polycrystalline Pr0.6Sr0.4Co1-yGayO3 (y=0.0-0.3) samples. Upon substitution of the non-magnetic Ga3+ cation for magnetic Co3+, the low-temperature ground state transforms from ferromagnetic metallic for y = 0 to cluster glass semiconductor for y = 0.2. Magnetoresistance at 7T is negative and its magnitude increases from 2 percentage for y = 0 to 30 percentage for y = 0.3 at 10 K. On the other hand, magnetostriction at 10 K is positive and its value decreases with increasing y. Interestingly, the field-dependent magnetization, magnetoresistance, and magnetostriction for y greater than or equal to 0.2 and at T less than or equal to 3 K show reversible abrupt steps for both positive and negative magnetic field whereas all these quantities vary smoothly with the magnetic field above 4 K. Such steps in all three distinct physical quantities were never reported earlier in perovskite cobaltites and they differ from observations made in manganites and intermetallic alloys. It is suggested that field-induced avalanche flipping of ferromagnetic clusters could be the origin of observed steps in all these three quantities.
The weak itinerant ferromagnet UIr is studied by magnetization and magnetostriction measurements. Critical behavior, which surprisingly extends up to several Tesla, is observed at the Curie temperature $T_C\simeq45$ K and is analyzed using Arrott and Maxwell relations. Critical exponents are found that do not match with any of the well-known universality classes. The low-temperature magnetization $M_s\simeq0.5$ $μ_B \cong const.$ below 3 T rises towards higher fields and converges asymptotically around 50 T with the magnetization at $T_C$. From the magnetostriction and magnetization data, we e…
We have demonstrated the effect of pressure on magnetization jump and its associated magnetostriction in Eu$_{0.58}$Sr$_{0.42}$MnO$_{3}$. The critical field lowered by the applied pressure is explained by a suppression of the metastable blocked state, which is inherent to the phase separated manganite system exhibiting the magnetic avalanche. To reduce a factor of the bad thermal coupling in the bulk sample, and to further examine the nature of the magnetization jump, we have performed the influence of pressure on the isothermal magnetization of the powder sample. There is no discrepancy in th…
We report an unusual giant linear magnetostrictive effect in the ferrimagnet Gd$_{2/3}$Ca$_{1/3}$MnO$_3$ ($T_{c} \approx$80 K). Remarkably, the magnetostriction, negative at high temperature ($T \approx T_{c}$), becomes positive below 15 K when the magnetization of the Gd sublattice overcomes the magnetization of the Mn sublattice. A rather simple model where the magnetic energy competes against the elastic energy gives a good account of the observed results and confirms that Gd plays a crucial role in this unusual observation. Unlike previous works in manganites where only striction associate…
The coupling of magnetic and electronic degrees of freedom to the crystal lattice in the ferromagnetic semimetal EuB$_6$, which exhibits a complex ferromagnetic order and a colossal magnetoresistance (CMR) effect, %, very likely involving magnetic polarons, is studied by high-resolution thermal expansion and magnetostriction experiments. EuB$_6$ may be viewed as a model system, where pure magnetism-tuned transport and the response of the crystal lattice can be studied in a comparatively simple environment,i.e., not influenced by strong crystal-electric field effects and Jahn-Teller distortions…
Cerium diantimonide (CeSb$_2$) is one of a family of rare earth based magnetic materials that exhibit metamagnetism, enabling control of the magnetic ground state through an applied magnetic field. At low temperatures, CeSb$_2$ hosts a rich phase diagram with multiple magnetically ordered phases for many of which the order parameter is only poorly understood. In this paper, we report a study of its metamagnetic properties by Scanning Tunneling Microscopy (STM) and magnetization measurements. We use STM measurements to characterize the sample magnetostriction with sub-picometer resolution from …
We investigated the magnetoelastic properties of the quasi-one-dimensional spin-1/2 frustrated magnet LiCuVO$_4$. Longitudinal-magnetostriction experiments were performed at 1.5 K in high magnetic fields of up to 60 T applied along the $b$ axis, i.e., the spin-chain direction. The magnetostriction data qualitatively resemble the magnetization results, and saturate at $H_{\text{sat}} \approx 54$ T, with a relative change in sample length of $ΔL/L \approx 1.8\times10^{-4}$. Remarkably, both the magnetostriction and the magnetization evolve gradually between $H_{\text{c3}} \approx 48$ T and $H_{\…
We present results on resistivity ($ρ$), magnetization ($M$), thermal conductivity ($κ$), magnetostriction ($\frac{ΔL}{L(0)}$) and specific heat ($C_{p}$) of charge-orbital ordered antiferromagnetic Nd$_{0.8}$Na$_{0.2}$MnO$_{3}$ compound. Magnetic field-induced antiferromagnetic/charge-orbital ordered insulating to ferromagnetic metallic transition leads to giant magnetothermal conductivity and magnetostriction effect. The low-temperature irreversibility behavior in $ρ$, $M$, $κ$ and $\frac{ΔL}{L(0)}$ due to field cycling together with striking similarity among the field and temperature depend…
We report the structural, magnetic, exchange bias and magnetotransport effect in Sr$_{4}$Fe$_{3}$CoO$_{11}$. The material crystallizes in the orthorhombic $\textit{Cmmm}$ space group. It shows antiferromagnetic (G-type) transition (T$_{N}$ = 255 K) along with interesting temperature induced magnetization reversal (T$_{Comp.}$= 47 K measured at 100 Oe). The magnetic reversal can be elucidated considering the increased magnetocrystalline anisotropy with Co substitution. Magnetoresistance measurements shows an interesting crossover from negative to positive side at $\sim$ 100 K. The negative magn…
Strong geometrical frustration in magnets leads to exotic states, such as spin liquids, spin supersolids and complex magnetic textures. SrCu2(BO3)2, a spin-1/2 Heisenberg antiferromagnet in the archetypical Shastry-Sutherland lattice, exhibits a rich spectrum of magnetization plateaus and stripe-like magnetic textures in applied fields. The structure of these plateaus is still highly controversial due to the intrinsic complexity associated with frustration and competing length scales. We reveal new magnetic textures in SrCu2(BO3)2 via magnetostriction and magnetocaloric measurements in fields …
We have investigated the temperature and magnetic field dependence of magnetization, specific heat ($C_p$), and relative sample length change ($ΔL/L_0$) for understanding the field-induced spin-structural change in quasi-one-dimensional spin chain $α$-CoV$_2$O$_6$ which undergoes antiferromagnetic (AFM) transition below $T_N$$=$15 K. Analysis of $C_p$($T$) shows that an effective $S$$=$1/2 Ising state is realized below 20 K, though the magnetic fluctuations persist well above $T_N$. $C_p$ and the coefficient of linear thermal expansion ($α$) exhibit strong $H$ dependence in the AFM state. We a…
We have investigated a single crystal of CeAgSb2 using low field ac-susceptibility, thermal expansion and magnetostriction measurements in the temperature range 1.5K to 90K. The ac-susceptibility exhibits a sharp peak at 9.7K for both B//c and B perp c due to the magnetic ordering of the Ce moment. The thermal expansion coefficient alpha, exhibits highly anisotropic behaviour between 3K and 80K : alpha is positive for dL/L perp c, but negative for dL/L // c. Furthermore, alpha (for dL/L) perp c (i.e. in ab-plane) exhibits a sharp peak at TN followed by a broad maximum at 20K, while a sharp neg…
Colossal magnetoresistance is of great fundamental and technological significance and exists mostly in the manganites and a few other materials. Here we report colossal magnetoresistance that is starkly different from that in all other materials. The stoichiometric Mn3Si2Te6 is an insulator featuring a ferrimagnetic transition at 78 K. The resistivity drops by 7 orders of magnitude with an applied magnetic field above 9 Tesla, leading to an insulator-metal transition at up to 130 K. However, the colossal magnetoresistance occurs only when the magnetic field is applied along the magnetic hard a…
We report the ground state magnetic structure and in-field magnetostrictive effects of NiTiO$_3$ studied by means of zero field and in-field single-crystal neutron diffraction, magnetization, and high-resolution dilatometry experiments. Zero-field neutron diffraction on NiTiO$_3$ single crystals reveals an easy-plane antiferromagnet with a multidomain ground state. Upon application of external magnetic fields, neutron diffraction shows the evolution of domains with spins perpendicular to the applied field. The rotation of spins in the multidomain state exhibits pronounced lattice changes in th…
We have studied the magnetization and magnetoresistance of CeRu2Al10 in the applied magnetic field H along the c-axis up to ~ 55 T. The magnetization M at low temperatures shows an H-linear increase with a small slope of M/H than that for H // a-axis up to ~ 55 T after showing a small anomaly at H ~ 4 T, which indicates that the critical field to the paramagnetic phase H_c^p is higher than 55 T for H // c-axis. The magnetization curves for H // a- and c-axes below the antiferro magnetic (AFM) transition temperature T0 behave as if the magnetic anisotropy in the AFM-ordered phase is small, alth…
We investigate the low temperature magnetic field dependences of both the resistivity and the magnetization in the misfit cobaltate Ca3Co4O9 from 60 K down to 2 K. The measured negative magnetoresistance reveals a scaling behavior with the magnetization which demonstrates a spin dependent diffusion mechanism. This scaling is also found to be consistent with a shadowed metalliclike conduction over the whole temperature range. By explaining the observed transport crossover, this result shed a new light on the nature of the elementary excitations relevant to the transport.
Magnetic field induced step-like changes in magnetization and resistivity of SmSr manganites were studied. A strong dependence of these features on the cooling rate was observed. Magnetostriction, however, does not show the presence of large strain in our samples. From all these features we can rule out the conventional explanation of magnetization jumps as a consequence of martensitic transition. We propose instead that quenched by fast cooling disorder leads to the formation of an inhomogeneous metastable state and to subsequent magnetization jumps.
We study TmB_4, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB_4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low-temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. We propose that complex structures at magnetic domain walls may be responsible for the hysteretic MR and may also lead…
We have measured high-field magnetization and magnetoresistance of polycrystalline samples of the A-site ordered perovskite CaCu3Ti4-xRuxO12 (x=0 - 4) utilizing a non-destructive pulsed magnet. We find that the magnetization for x=0.5, 1.0 and 1.5 is nonlinear, and tends to saturate in high fields. This is highly nontrivial because the magnetization for x=0 and 4 is linear in external field up to the highest one. We have analyzed this field dependence based on the thermodynamics of magnetic materials, and propose that the external fields delocalize the holes on the Cu2+ ions in order to maximi…
Spin-phonon coupling, the interaction of spins with surrounding lattice is a key parameter to understand the underlying physics of multiferroics and engineer their magnetization dynamics. Elementary excitations in multiferroic materials are strongly influenced by spin-phonon interaction, making Raman spectroscopy a unique tool to probe these coupling(s). Recently, it has been suggested that the dielectric and magnetic properties of 15R-type hexagonal BaMnO3 are correlated through the spin-lattice coupling. Here, we report the observation of an extensive renormalization of the Raman spectrum of…
We have studied a nearly stoichiometric insulating Y$_{0.97(2)}$Cr$_{0.98(2)}$O$_{3.00(2)}$ single crystal by performing measurements of magnetization, heat capacity, and neutron diffraction. Albeit that the YCrO$_3$ compound behaviors like a soft ferromagnet with a coersive force of $\sim$ 0.05 T, there exist strong antiferromagnetic (AFM) interactions between Cr$^{3+}$ spins due to a strongly negative paramagnetic Curie-Weiss temperature, i.e., -433.2(6) K. The coexistence of ferromagnetism and antiferromagnetism may indicate a canted AFM structure. The AFM phase transition occurs at $T_\tex…
We report on the temperature and field driven metal-insulator transition in disordered Ge:Mn magnetic semiconductors accompanied by magnetic ordering, magnetoresistance reaching thousands of percents and suppression of the extraordinary Hall effect by a magnetic field. Magnetoresistance isotherms are shown to obey a universal scaling law with a single scaling parameter depending on temperature and fabrication. We argue that the strong magnetic disorder leads to localization of charge carriers and is the origin of the unusual properties of Ge:Mn alloys.
The phenomena of odd-parity magnetoresistance and the planar Hall effect are deeply entwined with ferromagnetism. The intrinsic magnetization of the ordered state permits these unusual and rarely observed manifestations of Onsager's theorem when time reversal symmetry is broken at zero applied field. Here we study two classes of ferromagnetic materials, rare-earth magnets with high intrinsic coercivity and antiferromagnetic pyrochlores with strongly-pinned ferromagnetic layers at domain walls, which both exhibit odd-parity magnetoresistive behavior. The peculiar angular variation of the respon…
We performed a systematic study of the temperature- and field-dependence of magnetization and resistivity of Gd2PdSi3, which is a centrosymmetric skyrmion crystal. While the magnetization behavior is consistent with the reported phase diagram based on susceptibility, we show that a phase diagram can also be constructed based on the anomalous magnetoresistance with one-to-one correspondence among all the features. In addition, the crossover boundary into the field-induced ferromagnetic state is also identified. Our results suggest that the ferromagnetic spin fluctuations above the Néel temperat…
In this paper we study the switching properties of the dynamics of magnetic moments, that interact with an elastic medium. To do so we construct a Hamiltonian framework, that can take into account the dynamics in phase space of the variables that describe the magnetic moments in a consistent way. It is convenient to describe the magnetic moments as bilinears of anticommuting variables that are their own conjugates. However, we show how it is possible to avoid having to deal directly with the anticommuting variables themselves, only using them to deduce non-trivial constraints on the magnetoela…
The crystalline structure, anisotropic magnetoresistance (AMR), and magnetization of La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices grown by an rf sputtering system are systematically analyzed to study the spin polarization of manganite at interfaces. A perfectly epitaxial growth with sharp interfaces between LSMO and STO layers is confirmed by the transmission electron microscopy (TEM) image and the x-ray diffraction. The presence of positive low-temperature AMR in LSMO/STO superlattices with thinner LSMO layers or thicker STO layers implies that two bands of majority and minority character c…
We study an asymmetric in field magnetoresistance that is frequently observed in magnetic films and, in particular, the odd longitudinal voltage peaks that appear during magnetization reversal in ferromagnetic films, with out-of-plane magnetic anisotropy. We argue that the anomalous signals result from small variation of magnetization and Hall resistivity along the sample. Experimental data can be well described by a simple circuit model, the latter being supported by analytic and numerical calculations of current and electric field distribution in films with a gradual variation of the magneti…
We consider an array of XX spin-1/2 chains coupled to acoustic phonons and placed in a magnetic field. Treating the phonons in the mean field approximation, we show that this system presents a first order transition as a function of the magnetic field between a partially magnetized distorted state and the fully polarized undistorted state at low temperature. This behavior results from the magnetostriction of the coupled chain system. A dip in the elastic constant of the material near the saturation field along with an anomaly in the magnetic susceptibility is predicted. We also predict the con…
Tunneling surface current through a thin ferromagnetic barrier in a three-dimensional topological insulator is shown to possess an extraordinary response to the orientation of barrier magnetization. In contrast to conventional magnetoresistance devices that are sensitive to the relative alignment of two magnetic layers, a drastic change in the transmission current is achieved by a single layer when its magnetization rotates by 90 degrees. Numerical estimations predict a giant magnetoresistance as large as 800 % at room temperature and the proximate exchange interaction of 40 meV in the barrier…
We report a detailed study of the magnetic properties of CeCo$_{0.85}$Fe$_{0.15}$Si under high magnetic fields (up to 16 Tesla) measuring different physical properties such as specific heat, magnetization, electrical resistivity, thermal expansion and magnetostriction. CeCo$_{0.85}$Fe$_{0.15}$Si becomes antiferromagnetic at $T_N \approx$ 6.7 K. However, a broad tail (onset at $T_X \approx$ 13 K) in the specific heat precedes that second order transition. This tail is also observed in the temperature derivative of the resistivity. However, it is particularly noticeable in the thermal expansion …
We report the magnetostrictive length changes of CoTiO$_3$ studied by means of high-resolution dilatometry in magnetic fields ($B$) up to 15~T. In the long-range antiferromagnetically ordered phase below $T_N$ = 38~K, the easy-plane type spin structure undergoes a spin-reorientation transition in the $ab$ plane in magnetic fields $B || ab \approx 2$~T. We observe pronounced length changes driven by external magnetic field in this field region indicating significant magnetoelastic coupling in CoTiO$_3$. Specifically, we observe anisotropic deformation of the lattice for fields applied in the $a…
1/5 and 1/3 magnetization plateaux in the spin 1/2 chain system YbAlO3
Department of Applied Physics and Quantum-Phase Electronics Center, The University of Tokyo（东京大学应用物理与量子相电子中心）；Department of Physics, Technical University of Munich（慕尼黑工业大学物理系）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Technische Universität Dresden（德累斯顿工业大学）；Physikalisches Institut, Universitat Bonn（波恩大学物理研究所）；Laboratory for Neutron Scattering and Imaging, PSI Center for Neutron and Muon Sciences, Paul Scherrer Institut（保罗谢勒研究所中子与缪子科学中心中子散射与成像实验室）；Lviv Polytechnic National University（利沃夫国立理工大学）；Department of Physics and Astronomy, University of Utah（犹他大学物理与天文学系）
It is assumed that in a two-dimensional electron system with strong correlation (a Wigner liquid), appearance of some relatively slow-moving objects (clusters) composed of small number of electrons is possible. Such clusters may exist in addition to ordinary mobile carriers of the Fermi type. They can pin to inhomogeneities and play the role of additional scatterers. The clusters composed of two and three electrons are discussed (for near order as in triangular lattice). The number of the clusters depends on temperature and a parallel magnetic field (so accordingly for conductivity and magneti…
The longitudinal resistance $R_{xx}$ of the SrTiO3/LaAlO3 interface with magnetic fields applied perpendicular to the interface has an antisymmetric term (namely, $R_{xx}(H)\neq R_{xx}(-H)$) which increases with decreasing temperature and increasing field. We argue that the origin of this phenomenon is a non-homogeneous Hall effect with clear contribution of an extraordinary Hall effect, suggesting the presence of non-uniform field-induced magnetization.
SrRuO3 is an itinerant ferromagnet and in its thin film form when grown on miscut SrTiO3 it has Tc of ~ 150 K and strong uniaxial anisotropy. We measured both the Hall effect and the magnetoresistance (MR) of the films as a function of the angle between the applied field and the normal to the films at temperatures above Tc. We extracted the extraordinary Hall effect that is proportional to the perpendicular component of the magnetization and thus the MR for each angle of the applied field could be correlated with the magnitude and orientation of the induced magnetization. We successfully fit t…
Spinel Cobalt Vanadate CoV$_2$O$_4$ has been grown on (001) SrTiO$_3$ substrates. Using torque magnetometry experiments, we find that the previously observed temperature induced anisotropy change, where the easy axis changes from the out of plane [001] direction to a biaxial anisotropy with planar <100> easy axes, occurs in a gradual second-order structural phase transition. This work characterizes this transition and the magnetic anisotropies in the (001), (100), and (-110) rotation planes, and explores their field dependence up to 30~T. Below 80~K, hysteretic features appear around the hard …
We study the giant magnetoresistance of nanogranular magnets in the presence of an external magnetic field and finite temperature. We show that the magnetization of arrays of nanogranular magnets has hysteretic behaviour at low temperatures leading to a double peak in the magnetoresistance which coalesces at high temperatures into a single peak. We numerically calculate the magnetization of magnetic domains and the motion of domain walls in this system using a combined mean-field approach and a model for an elastic membrane moving in a random medium, respectively. From the obtained results, we…
Colossal Magnetoresistance and Phonon Driven Exchange Dynamics in Eu$_5$Sn$_2$As$_6$
University of Tokyo（东京大学）；University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；National High Magnetic Field Laboratory, Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室国家高磁场实验室）；Molecular Foundry, Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室分子发现中心）；Physikalisch-Technische Bundesanstalt（德国物理技术联邦研究院）
The results of dc magnetization, electrical and magnetoresistance and heat capacity measurements (2-300 K) on Tb7Rh3, crystallizing in Th7Fe3-type hexagonal structure, are reported. In this compound, magnetic ordering sets in around 90 K with additional transitions at low temperatures and the temperature coefficient of resistivity (R), dR/dT, is negative over a wide temperature range in the paramagnetic state. The present magnetization results reveal that this compound is apparently characterized by rich features in the magnetic-field-temperature phase diagram. A point of major emphasis is tha…
Magnetic properties of an antiferromagnetic double perovskite oxide Ba2CaReO6, where Re6+ (5d1) ions with large spin-orbit coupling are arranged on the face-centered-cubic lattice, are investigated using pulsed high magnetic field up to 66 T. Magnetization and magnetostriction measurements have revealed a magnetic field induced phase transition at around 50 T. The phase transition accompanies a jump of magnetization and longitudinal magnetostriction of approximately 2 10^(-4) with the change of power law behavior, indicating sizable coupling between the electronic degrees of freedom and the la…
We report detailed magnetization ($M$) and magnetoresistance ($MR$) studies on a series of Sr$_2$FeMoO$_6$ samples with independent control on anti-site defect and grain boundary densities. These results, exhibiting a switching-like behavior of $MR$ with $M$, establish that the $MR$ is controlled by the magnetic polarization of grain boundary regions, rather than of the grains within a resonant tunnelling mechanism.
We study the magnetic and transport properties of all-manganite heterostructures consisting of ferromagnetic metallic electrodes separated by an antiferromagnetic barrier. We find that the magnetic ordering in the barrier is influenced by the relative orientation of the electrodes magnetization producing a large difference in resistance between the parallel and antiparallel orientations of the ferromagnetic layers. The external application of a magnetic field in a parallel configuration also leads to large magnetoresistance.
We have investigated exchange bias effects in bilayers composed by the antiferromagnetic o-YMnO$_3$ and ferromagnetic Co thin film by means of SQUID magnetometry, magnetoresistance, anisotropic magnetoresistance and planar Hall effect. The magnetization and magnetotransport properties show pronounced asymmetries in the field and magnetization axes of the field hysteresis loops. Both exchange bias parameters, the exchange bias field $H_{E}(T)$ as well as the magnetization shift $M_E(T)$, vanish around the Néel temperature $T_N \simeq 45$ K. We show that the magnetization shift $M_E(T)$ is also …
Within massive gravity, we construct a gravity dual for insulator/metal phase transition and colossal magnetoresistance (CMR) effect found in some manganese oxides materials. In heavy graviton limit, a remarkable magnetic-field-sensitive DC resistivity peak appears at the Curie temperature, where an insulator/metal phase transition happens and the magnetoresistance is scaled with the square of field-induced magnetization. We find that metallic and insulating phases coexist below the Curie point and the relation with the electronic phase separation is discussed.
