arXiv subjects

H. Idzuchi

Publications and source records attributed to H. Idzuchi.

9 recordsLinked to original sources

arXiv2022

Spin sensitive transport in RuCl_3/Pt heterostructures: revealing a field-transverse spin anisotropy in a spin liquid candidate

Alpha-phase (a-) RuCl_3 has emerged as a possible candidate for a quantum spin liquid (QSL) that promises exotic quasi-particles relevant for fault-tolerant quantum computation. Here, we report spin-sensitive transport measurements using a proximal spin Hall metal -- platinum (Pt) -- to probe magnetic moments in the insulator a-RuCl_3. We observe a spin Hall magnetoresistance (SMR) where both the transverse and longitudinal resistivities of a-RuCl_3/Pt exhibit oscillations as functions of the angle between the in-plane magnetic field and the current, arising from the interplay between the spin Hall effect in Pt and local magnetic moments in a-RuCl3. The oscillations are observed from 1.5 T to 18 T, spanning the range of magnetic fields where zig-zag antiferromagnetic phase, the putative QSL phase, and the partially field-polarized states are reported in a-RuCl_3. The phase of the SMR oscillations suggest that the local moments, regardless of static or fluctuating, in a-RuCl_3 develop an anisotropy with an in-plane quantization axis that aligns largely transverse to the magnetic field for all fields above 1.5 T. Temperature dependance of the SMR revealed that the spin anisotropy has a similar energy scale to reported QSL signatures in a-RuCl_3. The coupling between the spin states within a-RuCl_3 and Pt demonstrated in our experiment opens a transport route to exploring exotic spin phases and device functionalities of QSL materials.

cond-mat.str-el↗

arXiv2020

Van der Waals Heterostructure Magnetic Josephson Junction

When two superconductors are connected across a ferromagnet, the spin configuration of the transferred Cooper pairs can be modulated due to magnetic exchange interaction. The resulting supercurrent can reverse its sign across the Josephson junction (JJ) [1-4]. Here we demonstrate Josephson phase modulation in van der Waals heterostructures when Cooper pairs from superconducting NbSe$_2$ tunnel through atomically thin magnetic insulator (MI) Cr$_2$Ge$_2$Te$_6$. Employing a superconducting quantum interference device based on MI JJs, we probe a doubly degenerate non-trivial JJ phase ($ϕ$) originating from the magnetic barrier. This $ϕ$-phase JJ is formed by momentum conserving tunneling of Ising Cooper pairs [5] across magnetic domains in the Cr$_2$Ge$_2$Te$_6$ barrier. The doubly degenerate ground states in MI JJs provide a two-level quantum system that can be utilized as a new disipationless component for superconducting quantum devices, including phase batteries [6], memories [7,8], and quantum Ratchets [9,10].

cond-mat.mes-hall↗

arXiv2020

Spin injection characteristics of Py/graphene/Pt by gigahertz and terahertz magnetization dynamics driven by femtosecond laser pulse

Spin transport characteristics of graphene has been extensively studied so far. The spin transport along c-axis is however reported by rather limited number of papers. We have studied spin transport characteristics through graphene along c-axis with permalloy(Py)/graphene(Gr)/Pt by gigahertz (GHz) and terahertz (THz) magnetization dynamics driven by femtosecond laser pulses. The relatively simple sample structure does not require electrodes on the sample. The graphene layer was prepared by chemical vapor deposition and transferred on Pt film. The quality of graphene layer was characterized by Raman microscopy. Time resolved magneto-optical Kerr effect is used to characterize gigahertz magnetization dynamics. Magnetization precession is clearly observed both for Pt/Py and Pt/Gr/Py. The Gilbert damping constant of Pt/Py was 0.015, indicates spin pumping effect from Py to Pt. The Gilbert damping constant of Pt/Gr/Py is found to be 0.011, indicates spin injection is blocked by graphene layer. We have also performed the measurement of THz emission for Pt/Py and Pt/Gr/Py. While the THz emission is clearly observed for Pt/Py, a strong reduction of THz emission is observed for Pt/Gr/Py. With these two different experiments, and highly anisotropic resistivity of graphite, we conclude that the vertical spin transport is strongly suppressed by the graphene layer.

cond-mat.mes-hall↗

arXiv2019

Increased Curie temperature and enhanced perpendicular magneto anisotropy of Cr2Ge2Te6/NiO heterostructure

Magnetism in two-dimensional van der Waals materials has received significant attention recently. The Curie temperature reported for those materials, however, has been so far remained relatively low. Here, we measure magneto-optical Kerr effects (MOKE) under perpendicular magnetic field for van der Waals ferromagnet Cr2Ge2Te6 as well as its heterostructure with antiferromagnetic insulator NiO. We observe a notable increase in both Curie temperature and magnetic perpendicular anisotropy in Cr2Ge2Te6/NiO heterostructures compared to those in Cr2Ge2Te6. Measurements on the same exfoliated Cr2Ge2Te6 flake (on a SiO2/Si substrate) before and after depositing NiO show that the hysteresis loop can change into a square shape with larger coercive field for Cr2Ge2Te6/NiO. The maximum Curie temperature (TC) observed for Cr2Ge2Te6/NiO reaches ~120 K, is nearly twice the maximum TC ~ 60 K reported for Cr2Ge2Te6 alone. Both enhanced perpendicular anisotropy and increased Curie temperature are observed for Cr2Ge2Te6 flakes with a variety of thicknesses ranging from ~5 nm to ~200 nm. The results indicate that magnetic properties of two-dimensional van der Waals magnets can be engineered and controlled by using the heterostructure interface with other materials.

cond-mat.mes-hall↗

arXiv2017

Tunneling Devices with Perpendicular Magnetic Anisotropy Electrodes on Atomically Thin van der Waals Heterostructures

We report the fabrication of perpendicular ferromagnetic electrodes for tunneling devices consist of van der Waals heterostructure. We found MgO/Co/Pt films on Hexagonal BN shows perpendicular magnetic anisotropy (PMA) with the easy axis perpendicular to the substrate. Vacuum annealing enhances the perpendicular anisotropy. The easy axis along the perpendicular direction persists up to room temperature with the Pt layer thickness ranges from 1.5 to 5 nm. We employed the PMA electrodes to construct tunneling devices on graphene and monolayer WSe2, where spin injection characteristics and field effect transistor behavior were demonstrated without strong Schottky barrier formation.

cond-mat.mes-hall↗

arXiv2014

Revisiting the measurement of the spin relaxation time in graphene-based devices

A long spin relaxation time (tausf) is the key for the applications of graphene to spintronics but the experimental values of tausf have been generally much shorter than expected. We show that the usual determination by the Hanle method underestimates tausf if proper account of the spin absorption by contacts is lacking. By revisiting series of experimental results, we find that the corrected tausf are longer and less dispersed, which leads to a more unified picture of tausf derived from experiments. We also discuss how the correction depends on the parameters of the graphene and contacts.

cond-mat.mes-hall↗

arXiv2013

Effect of anisotropic spin absorption on the Hanle effect in lateral spin valves

We have succeeded in fully describing dynamic properties of spin current including the different spin absorption mechanism for longitudinal and transverse spins in lateral spin valves, which enables to elucidate intrinsic spin transport and relaxation mechanism in the nonmagnet. The deduced spin lifetimes are found independent of the contact type. From the transit-time distribution of spin current extracted from the Fourier transform in Hanle measurement data, the velocity of the spin current in Ag with Py/Ag Ohmic contact turns out much faster than that expected from the widely used model.

cond-mat.mes-hall↗

arXiv2012

Spin relaxation mechanism in Silver nanowires covered with MgO protection layer

Spin-flip mechanism in Ag nanowires with MgO surface protection layers has been investigated by means of nonlocal spin valve measurements using Permalloy/Ag lateral spin valves. The spin flip events mediated by surface scattering are effectively suppressed by the MgO capping layer. The spin relaxation process was found to be well described in the framework of Elliott-Yafet mechanism and then the probabilities of spin-filp scattering for phonon or impurity mediated momentum scattering is precisely determined in the nanowires. The temperature dependent spin-lattice relaxation follows the Bloch-Grüneisen theory and falls on to a universal curve for the monovalent metals as in the Monod and Beuneu scaling determined from the conduction electron spin resonance data for bulk.

cond-mat.mes-hall↗

arXiv2011

Giant enhancement of spin accumulation and long-distance spin precession in metallic lateral spin valves

The nonlocal spin injection in lateral spin valves is highly expected to be an effective method to generate a pure spin current for potential spintronic application. However, the spin valve voltage, which decides the magnitude of the spin current flowing into an additional ferromagnetic wire, is typically of the order of 1 μV. Here we show that lateral spin valves with low resistive NiFe/MgO/Ag junctions enable the efficient spin injection with high applied current density, which leads to the spin valve voltage increased hundredfold. Hanle effect measurements demonstrate a long-distance collective 2-pi spin precession along a 6 μm long Ag wire. These results suggest a route to faster and manipulable spin transport for the development of pure spin current based memory, logic and sensing devices.

cond-mat.mes-hall↗