Simultaneous MOKE imaging and measurement of magneto-resistance with vector magnet: a low noise customized setup for low field magnetic devices and thin films characterization
Imtiaz Noor Bhatti, Ilyas Noor Bhatti, L. G. Enger, P. Victor, B. Guillet, M. Lam Chok Sing, O. Rousseau, V. Pierron, S. Lebargy, J. Camarero, L. Mechin, S. Flament
Here we report a custom design setup for the simultaneous measurement of magneto-resistance and MOKE imaging in longitudinal configuration for characterization of magnetic thin-films and sensors. The setup is designed so as to cope with a small signal to noise ratio of initial images and to allow sensitive magnetoresistance (MR) measurement at low field. An improved differential algorithm is used to get a good enough contrast of the magnetic images and get rid of beam illumination or small camera gain fluctuations. Home made power supply and pre-amplifier stage were designed so as to reduce the low frequency noise as well as the thermal electrical noise. A vector magnet is used to produce rotational magnetic field so as to study the magnetic anisotropy and calculate the anisotropic constants in magnetic thin films. Magnetoresistive sensors patterned on epitaxial La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) thin film have been characterized with this setup. The Images of the magnetization reversal process as well as the local magnetization loops deduced from these images provided evidence of a magnetic uniaxial anisotropy induced by the vicinal substrate. The magnetic anistropic constant of the films was then inferred from the MR measurements.
Domain imaging, MOKE and magnetoresistance studies of CoFeB films for MRAM applications
我们提出了一个详细的研究领域的成像，克尔效应磁强计（MOKE）和磁阻（MR），为一系列的20 nm的钴$_{73.8}$铁$_{16.2}$ B $_{10}$薄膜，作为沉积（非晶）和退火（结晶）。通过考虑两个不同的（正交）面内磁化分量，通过MOKE测量获得，我们能够研究CoFeB沉积过程中诱导的单轴各向异性，并区分平行和垂直于这样的轴的磁场下的磁化过程。MOKE磁成像使我们能够观察到占主导地位的磁化过程，即畴壁运动和磁矩旋转。这些过程与磁电阻的行为，这取决于短程自旋无序电子散射和电流和自发磁化（$\emph{\textbf{M}}_{S}$）之间的角度。一个简单的数值处理的基础上Stoner-Wolfarth模型，使我们能够满意地预测在这些薄膜中观察到的磁化行为。在Co $_{73.8}$ Fe $_{16.2}$ B $_{10}$膜中的结果与先前在退火Co $_{80}$ Fe $_{20}$膜中获得的结果之间的比较表明，在CoFe中引入硼显著地降低了沿易磁化轴的矫顽场和饱和场（例如，$H_{c}$从$\sim$ 2下降到$\sim$ 0.5 kAm $^{-1}$）。此外，沿难磁化轴的磁化饱和在较低的领域。我们得出结论，非晶和纳米晶CoFeB薄膜显示低矫顽场和突然切换，以及切换后的短程自旋无序效应的情况下相比，Co $_{80}$ Fe $_{20}$。
When a polarized light beam is incident upon the surface of a magnetic material, the reflected light undergoes a polarization rotation. This magneto-optical Kerr effect (MOKE) has been intensively studied in a variety of ferro- and ferrimagnetic materials because it provides a powerful probe for electronic and magnetic properties as well as for various applications including magneto-optical recording. Recently, there has been a surge of interest in antiferromagnets (AFMs) as prospective spintronic materials for high-density and ultrafast memory devices, owing to their vanishingly small stray f…
An alternate method of measuring anisotropy fields in thin film ferromagnets is demonstrated. The method relies on the magnetic susceptibility in a small a.c. magnetic field, measured \txtit{in situ} using the magneto-optic Kerr effect (MOKE), and will be useful in situations where more specialized apparatus are not available, or constraints discourage the use of a large, static magnetic field. The method is demonstrated for Co/W(110) films, where it yields anisotropy fields in agreement with previous studies using more conventional torque magnetometry. The sensitivity of the method is demonst…
Using symmetry arguments and a tight-binding model, we show that for layered collinear anti- ferromagnets, magneto-optic effects can be generated and manipulated by controlling crystal symmetries through a gate voltage. This provides a promising route for electric field manipulation of the magneto-optic effects without modifying the underlying magnetic structure. We further demonstrate the gate control of magneto-optic Kerr effect (MOKE) in bilayer MnPSe3 using first-principles calculations. The field-induced inversion symmetry breaking effect leads to gate-controllable MOKE whose direction of…
The magneto-optical Kerr effect (MOKE) is often assumed to be proportional to the magnetisation of a magnetically ordered metallic sample; in metallic ferrimagnets with chemically distinct sublattices, such as rare-earth transition-metal alloys, it depends on the difference between the sublattice contributions. Here we show that in a highly spin polarized, fully compensated ferrimagnet, where the sublattices are chemically similar, MOKE is observed even when the net moment is strictly zero. We analyse the spectral ellipsometry and MOKE of Mn 2 Ru x Ga, and show that this behaviour is due to a …
Previous studies on the anomalous Hall effect in coplanar non-collinear antiferromagnets are revisited and extended to magneto-optic properties, namely magneto-optic Kerr effect (MOKE) and X-ray magnetic dichroism (XMCD). Starting from group-theoretical considerations the shape of the frequency-dependent conductivity tensor for various actual and hypothetical spin configurations in cubic and hexagonal Mn$_3X$ compounds is determined. Calculated MOKE and X-ray dichroism spectra are used to confirm these findings and to give estimates of the size of the effects. For Mn$_3$IrPt and Mn$_3$PtRh all…
Magneto-optical Kerr effect in an A-type antiferromagnet
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）；Institute of Science and Technology Austria（奥地利科学技术研究院）；University of Kansas（堪萨斯大学）；Chalmers University of Technology（查尔姆斯理工大学）；University of Cambridge（剑桥大学）；Oak Ridge National Laboratory（橡树岭国家实验室）
Magneto-optical signal from $\mathrm{Co_2Mn}$-based Heusler thin films in MOKE and BLS
Institute of Physics, Czech Academy of Sciences（捷克科学院物理研究所）；Laboratoire d’Ecologie Alpine, Université Grenoble Alpes, CNRS（阿尔卑斯生态实验室，格勒诺布尔阿尔卑斯大学，法国国家科学研究中心）；École Normale Supérieure Paris-Saclay（巴黎萨克雷高等师范学院）
Magneto-optical Kerr effect (MOKE) is an efficient approach to probe surface magnetization in thin film samples. Here we present a wide-field MOKE technique that adopts a K$ö$hler illumination scheme to characterize the current-induced damping-like spin-orbit torque (DL-SOT) in micronsized and unpatterned magnetic heterostructures with perpendicular magnetic anisotropy. Through a current-induced hysteresis loop shift analysis, we quantify the DL-SOT efficiency of a Ta-based heterostructure with bar-shaped geometry, Hall-cross geometry, and unpatterned geometry to be $|ξ_{DL}|\approx$ 0.08. The…
Polar and quadratic magneto-optical Kerr effects in nonmagnetic/ferromagnet bilayers for spin-orbit torque measurements
The University of Tokyo（东京大学）；Research Institute of Electrical Communication (RIEC), Tohoku University（东北大学电气通信研究所）；Mie University（三重大学）；Trans-scale quantum science institute (TSQS), The University of Tokyo（东京大学跨尺度量子科学研究所）
Magnetic and spintronic media have offered fundamental scientific subjects and technological applications. Magneto-optic Kerr effect (MOKE) microscopy provides the most accessible platform to study the dynamics of spins, magnetic quasi-particles, and domain walls. However, in the research of nanoscale spin textures and state-of-the-art spintronic devices, optical techniques are generally restricted by the extremely weak magneto-optical activity and diffraction limit. Highly sophisticated, expensive electron microscopy and scanning probe methods thus have come to the forefront. Here, we show th…
Magneto-optical evidence for single-crystal-like magnetic switching of epitaxial antiferromagnetic LaFeO3 films
Martin-Luther-Universität Halle-Wittenberg（哈勒-维滕贝格马丁路德大学）；Helmholtz-Zentrum Berlin für Materialien und Energie GmbH（柏林亥姆霍兹材料与能源中心有限公司）；University of Potsdam（波茨坦大学）
We investigate theoretically an angle dependence of enhancement of polar magneto-optical Kerr effect (MOKE) obtained thanks to a deposition of a paramagnetic Diluted Magnetic Semiconductor (DMS) layer on one-dimensional photonic crystal layer. Our transfer matrix method based calculations conducted for TE and TM polarizations of the incident light predict up to an order of magnitude stronger MOKE for a (Ga,Fe)N DMS layer when implementing the proposed design. The maximum enhancement for TE and TM polarization occurs for the light incidence at the normal and at the Brewster angle, respectively.…
We carried out magneto-optical Kerr effect (MOKE) and magnetization measurements on a single crystal of Ni2.00Mn1.16Ga0.84 in a longitudinal geometry. While there had been reports of polar geometry measurements so far, we show that - against earlier predictions - surface magnetic states of the martensite and the austenite can be also probed efficiently via longitudinal MOKE. A single variant magnetic state, which occurs at room temperature, is characterized by ferromagnetic hysteresis loops similar to standard ferromagnets. Temperature dependencies of Kerr rotation were found to be linearly pr…
We report a giant enhancement of the mid-infrared (MIR) magneto-optical complex Kerr angle (polarization change of reflected light) in a variety of materials grown on SiC. In epitaxially-grown multilayer graphene, the Kerr angle is enhanced by a factor of 68, which is in good agreement with Kerr signal modeling. Strong Kerr enhancement is also observed in Fe films grown on SiC and Al-doped bulk SiC. Our experiments and modelling indicate that the enhancement occurs at the high-energy edge of the SiC reststrahlen band where the real component of the complex refractive index n passes through uni…
Current induced magneto-optical Kerr effect as a probe of Dirac carriers in Bi$_{1-x}$Sb$_x$ alloy
The University of Tokyo（东京大学）；University of California, Irvine（加州大学尔湾分校）；RIKEN Center for Emergent Matter Science (CEMS)（理化学研究所新兴物质科学中心）；Research Institute of Electrical Communication (RIEC), Tohoku University（东北大学电波研究所）；Trans-scale Quantum Science Institute, The University of Tokyo（东京大学跨尺度量子科学研究所）
We report the magneto optic Kerr effect (MOKE) angle of Au magnetically excited by spin accumulation. We perform time resolved polar MOKE measurements on Au/Co heterostructures. In our experiment, the ultrafast optical excitation of the Co drives spin accumulation into an adjacent Au layer. The spin accumulation, together with spin-orbit coupling, leads to non-zero terms in the off-diagonal conductivity tensor of Au, which we measure by recording the polarization and ellipticity of light reflected from the Au surface for photon energies between 1.3 and 3.1 eV. At energies near the interband tr…
Co /CoO/Co polycrystalline film was grown on Si (001) substrate and magnetic properties have been investigated using in-situ magneto-optic Kerr effect during growth of the sample. Magnetic anisotropy with easy axis perpendicular to the film surface has been observed in top Co layer, whereas bottom layer was found to be soft with in-plane magnetization without any influence of top layer. Ex-situ in-plane and out-of-plane diffraction measurements revealed that the growth of Co on oxidized interface takes place with preferential orientation of c-axis perpendicular to the film plane, which results…
In the non-collinear antiferromagnet Mn$_3$Sn, we compare simultaneous measurements of the anomalous Hall effect (AHE) and the magneto-optical Kerr effect (MOKE) through two magnetic phase transitions: the high-temperature paramagnetic/antiferromagnetic phase transition at the Néel temperature ($T_N \approx$420~K), and a lower-temperature incommensurate magnetic ordering at $T_1 \approx$270~K. While both the AHE and MOKE are sensitive to the same underlying symmetries of the antiferromagnetic non-collinear spin order, we find that the transition temperatures measured by these two techniques un…
Materials with no net magnetization are generally not magneto-optically active. While this is individually true for a collinear antiferromagnet (AFM) and a topological insulator (TI), it is shown here that the magneto-optic Kerr effect (MOKE) emerges when the TI and AFM films are proximity coupled. Because of the lack of macroscopic magnetization, the AFM only couples to the spin of one of the TI's surfaces breaking time-reversal and inversion symmetry -- which leads to a tiny $μ$deg MOKE signal. This small MOKE can be easily enhanced by 5 orders of magnitude, via cavity resonance, by optimizi…
The linear magneto-optical Kerr effect (MOKE) is often used to probe magnetism of ferromagnetic materials, but MOKE cannot be applied to collinear antiferromagnets (AFs) due to the cancellation of sub-lattice magnetization. Magneto-optical constants that are quadratic in magnetization, however, provide an approach for studying AFs on picosecond time scales. Here, we combine transient measurements of optical reflectivity and birefringence to study the linear optical response of Fe$_{2}$As to small ultrafast temperature excursions. We performed temperature dependent pump-probe measurements on cr…
Element-selective techniques are central for the understanding of ultrafast spin dynamics in multi-element materials like magnetic alloys. Recently, though, it turned out that the commonly used technique of transverse magneto-optical Kerr effect (T-MOKE) in the EUV range may have linearity issues including unwanted cross talk between different elemental signals. This problem can be sizeable, which puts recent observations of ultrafast spin transfer from Fe to Ni sites in FeNi alloys into question. In this study, we investigate the Fe-to-Ni spin transfer in a cross-talk-free time-resolved X-ray…
We present a simple and effective instrument for simultaneous real-time imaging and hysteresis of the anisotropic magnetic domain dynamics in thin films using the Magneto-Optical Kerr Effect (MOKE). We furthermore illustrate that magnetic imaging allows a more accurate interpretation of the magnetization reversal processes than the conventional hysteresis characterization. In particular, we present a case where the onset of a double-step reversal observed in imaging remains invisible in the spatially integrated hysteresis loops. When complemented by precise tuning of the external magnetic fiel…
利用纵向磁光克尔效应（MOKE）和感应磁通测量法，对Fe $_{73.5}$ Cu $_1$ Nb $_3$ Si $_13.5$ B $_9$三个系列的Finemet薄膜进行了一系列的动态磁滞回线测量。的MOKE动态磁滞回线显示出更显着的变化与频率比电感的，而这两种测量显示出类似的依赖于频率的平方根。我们在一个简单的畴壁脱钉模型的框架中分析这些结果，该模型解释了数据的一般行为。
Evolution of magnetization behaviour of cobalt film on nano patterned silicon substrate, with film thickness, has been studied. In situ magneto-optical Kerr effect measurements during film deposition allowed us to study genuine thickness dependence of magnetization behaviour, all other parameters like surface topology, deposition conditions remaining invariant. The film exhibits uniaxial magnetic anisotropy, with its magnitude decreasing with increasing film thickness. Analysis shows that anisotropy has contributions from both, i) exchange energy which is volume dependent and, ii) stray dipola…
Co2FeAl (CFA) thin films with thickness varying from 10 nm to 115 nm have been deposited on MgO(001) substrates by magnetron sputtering and then capped by Ta or Cr layer. X-rays diffraction (XRD) revealed that the cubic $[001]$ CFA axis is normal to the substrate and that all the CFA films exhibit full epitaxial growth. The chemical order varies from the $B2$ phase to the $A2$ phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer measurements show that, depending on the field orientation, one or two-step switchings occur. Moreover, the films …
We propose a theoretical design of a structure combining a diluted magnetic semiconductor (DMS) layer with one-dimensional photonic crystal and show that it allows for a sizable (a few-fold) enhancement of the magneto-optical Kerr effect (MOKE) magnitude. We base our calculations on the transfer matrix method assuming realistic, and optimal with respect to a sample growth, parameters. We investigate representative cases of (Ga,Mn)N or (Cd,Mn)Te DMS layers deposited on the top of a respectively GaN- or CdTe-based distributed Bragg reflector, and highlight the applicability of the proposed desig…
Observation of large perpendicular magnetic anisotropy and excessive polar magneto-optical effect in Pt/CoFeB/Ru tri-layer system
Indian Institute of Technology Kanpur（坎普尔印度理工学院）；UGC-DAE Consortium for Scientific Research（UGC-DAE科学研究联盟）；Forschungszentrum Jülich（于利希研究中心）；Kyushu Institute of Technology（九州工业大学）
Spin-dependent charge transport in magnetic tunnel junctions (MTJs) can be manipulated by a temperature gradient, which can be utilized for spintronic and spin caloritronic applications. Evaluation of the thermally induced phenomena requires knowledge of the temperature differences across the oxide tunnel barrier adjacent to the ferromagnetic (FM) leads. However, it is challenging to accurately measure thermal properties of an oxide tunnel barrier consisting of only a few atomic layers. In this work, we experimentally interrogate the temperature evolutions in Ru/oxide/FM/seed/MgO (oxide=MgO, M…
Using a time-resolved magneto-optical Kerr effect (TR-MOKE) microscope, we observed ultrafast demagnetization of inverse-spinel-type NiCo2O4 (NCO) epitaxial thin films of the inverse spinel type ferrimagnet NCO with perpendicular magnetic anisotropy. This microscope uses a pump-probe method, where the sample is pumped at 1030 nm, and magnetic domain images are acquired via MOKE microscopy at 515 nm (the second harmonic). We successfully observed the dynamics of the magnetic domain of the NCO thin film via laser irradiation, and obtained a demagnetization time constant of approximately 0.4 ps. …
Hydrogenation-induced noncollinear magnetic anisotropy is observed from the evolution of the magnetic domains in FePd alloy thin films using magneto-optic Kerr effect (MOKE) microscopy. MOKE images reveal complicated competitions between different magnetic anisotropies during hydrogen diffusion into the film. An intriguing enhancement of the hydrogen diffusion rate due to the presence of an initial exchange bias induced by a high magnet field is thereby discovered, pointing to an additional scope of controllability of magnetic metal hydrides as potential future hydrogen sensing and storage mat…
We investigated the structural and magnetic properties of bare SrRuO$_3$ (SRO) ultra-thin films and SrRuO$_3$/SrIrO$_3$/SrZrO$_3$ (SRO/SIO/SZO: RIZ) trilayer heterostructures between 10 K and 80 K, by comparing macroscopic data using magneto-optical Kerr effect (MOKE) and magneto-transport (anomalous Hall effect: AHE), with nanoscale fingerprints when applying non-contact scanning force microscopy (nc-SFM) and magnetic force microscopy (MFM). SRO and RIZ ultra-thin films were epitaxially grown at 650C onto vicinal SrTiO$_3$ (100) single-crystalline substrates to a nominal thickness of 4 and 4/…
Spintronics exploits the magnetoresistance effects to store or sense the magnetic information. Since the magnetoresistance strictly depends on the magnetic anisotropy of the system, it is fundamental to set a defined anisotropy to the system. Here, we investigate by means of vectorial Magneto-Optical Kerr Magnetometry (v-MOKE), half-metallic La0.67Sr0.33MnO3 (LSMO) thin films that exhibit at room temperature pure biaxial magnetic anisotropy if grown onto MgO (001) substrate with a thin SrTiO3 (STO) buffer. In this way, we can avoid unwanted uniaxial magnetic anisotropy contributions that may b…
Black phosphorus (BP) has emerged as a direct-bandgap semiconducting material with great application potentials in electronics, photonics, and energy conversion. Experimental characterization of the anisotropic thermal properties of BP, however, is extremely challenging due to the lack of reliable and accurate measurement techniques to characterize anisotropic samples that are micrometers in size. Here, we report measurement results of the anisotropic thermal conductivity of bulk BP along three primary crystalline orientations, using the novel time-resolved magneto-optical Kerr effect (TR-MOKE…
