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Eiji Sasaki,1 Seiya Ota,1,2 Daisuke Chiba,1 Yuka Kimura,1 Shizuka Sasaki,1 Masataka Ando,2 Yuji Yamamoto,1 Eiichi Tsuda,3 Yasuyuki Ishibashi1 1Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, Hirosaki, Japan; 2Department of Social Medicine, Hirosaki University Graduate School of Medicine, Hirosaki, Japan; 3Department of Rehabilitation Medicine, Hirosaki University Graduate School of Medicine, Hirosaki, JapanCorrespondence: Eiji SasakiDepartment of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori, 036-8562, JapanTel +81-172-39-5083Fax +81-172-36-3826Email e_sasaki@hirosaki-u.ac.jpPurpose: Knee pain is associated with osteoarthritis (OA) and increases during this condition; however, its correlation with central sensitization (CS) in arthritis patients requires greater understanding. The present cross-sectional cohort study to explore the prevalence of knee OA, nocturnal knee pain and disability in general population and to examine the association of CS with sleep quality in Japanese general population.Patients and Methods: From among 1056 community-dowelling volunteers, 942 were enrolled as participants in this study. Bilateral weight-bearing anterior-posterior knee radiographs were classified by the Kellgren–Lawrence grade. Nocturnal knee pain and disability were assessed with self-reported questionnaires. Using the CS inventory with nine items (CSI-9), CS was defined as 10 points or higher. Sleep quality was scored using the Pittsburgh Sleep Quality Index (PSQI). Linear regression analysis, adjusted by age, sex, body mass index, Kellgren-Lawrence grade, nocturnal knee pain, and lifestyle habits, was performed to investigate the association of CS with PSQI.Results: The prevalence of OA, nocturnal knee pain, and disability was 37.9%, 7.6%, and 6.2%, respectively. The mean CSI-9 score was 4.9 ± 4.4, with a CS prevalence of 14.0%. The mean PSQI score was 3.9 ± 2.4, which was correlated with the CSI-9 value. CS was not correlated with OA severity; however, nocturnal knee pain prevalence increased from 13.3% to 25.5% in knee OA patients with CS. The CSI-9 value correlated with PSQI total score and subscales.Conclusion: Knee OA severity correlated with nocturnal pain and disability; however, its association with CS was unproven. The combined effect of knee OA and CS elevated nocturnal pain and disability, resulting in diminished sleep quality.Keywords: central sensitization, epidemiology, knee osteoarthritis, nocturnal knee pain, sleep quality

Recently, to enlarge spin-current-induced phenomena, such as spin–orbit torque (SOT) in a ferromagnet (FM)/heavy-metal (HM) bilayer, enhancement of spin-current transmittance by inserting an antiferromagnetic insulator at the FM/HM interface has been extensively studied. In this study, we have investigated the SOT modulation in a Pt/NiO/Co structure in which the NiO layer was deposited using Ar and Xe process gases. Consequently, the quality of the NiO layer could be regulated. An increase in the damping-like SOT efficiency was observed by inserting the 1 nm NiO layer in the Ar type while it monotonically decreased with an increase in the NiO thickness in the Xe type. Significant temperature dependence of the SOT efficiency in the Ar type indicates that thermal magnon largely contributes to the spin-current propagation. X-ray diffraction measurement result suggests that the difference in crystallinity of the NiO layer between the Ar and Xe types attributes to the different SOT modulations. [ABSTRACT FROM AUTHOR]

10.1063/5.0128531 9 H. Ekawa, J. Shen, K. Toyoki, R. Nakatani, and Y. Shiratsuchi, " Gate-induced switching of perpendicular exchange bias with very low coercivity in Pt/Co/Ir/Cr2O3/Pt epitaxial film", Appl. Phys. While W and Ta heavily degrade the magnetic response, Pt can be used to move from gate-induced effects within the PMA regime in CoFeB/MgO to a nonvolatile and reversible gate-induced spin-reorientation transition in CoFeB/Pt/MgO. Lu I et al. i [12] show that in IrMn/W/CoFeB/MgO/CoFeB based MTJs the exchange bias field allows for field-free SOT switching while the VCMA effect combined with Joule heating can significantly reduce the coercivity. A large portion of the ongoing research in spintronics is focused on advancing magnetic memory designs to not only provide improved capabilities but also operate with minimal power consumption. [Extracted from the article]

In a perpendicularly magnetized (PM) material with the interfacial Dzyaloshinskii–Moriya interaction (iDMI), a chirality-induced effective magnetic field (EMF) acts on a magnetic domain wall, which is a naturally formed in-plane magnetized (IM) region sandwiched by perpendicular (PM) regions. In this study, we artificially created a Pt/Co/MgO system with the regions exhibiting different anisotropy, that is, IM and PM regions, and the chirality-induced EMF at the PM/IM boundary was investigated using it. The EMF in the IM region was probed using magnetoresistance (MR) measurements. When the field was applied orthogonally to the wire, a unidirectional shift of the MR curve was observed, indicating that the EMF exists in the IM region. The dependence of the EMF on the width of the IM region suggests that the EMF acts dominantly on the magnetization near the PM/IM boundary. Moreover, the sign of the shift is reversed with reversing the PM direction. The sign and magnitude of the EMF observed in this study suggest that the EMF in the present system is caused by iDMI. [ABSTRACT FROM AUTHOR]

Conventional semiconductor devices use electric fields to control conductivity, a scalar quantity, for information processing. In magnetic materials, the direction of magnetization, a vector quantity, is of fundamental importance. In [...]

The switching of the magnetization direction induced by the spin-orbit torque in a perpendicularly magnetized Pt/Co/Pd structure has been investigated using X-ray magnetic circular dichroism. An electrical current injected parallel to the layers generates a spin current in a direction that is normal to the current in the Pt layer, and this spin current is generally considered to exert a torque on the adjacent ferromagnetic Co layer. A part of the Pt layer itself, however, is also in a ferromagnetic state, owing to the ferromagnetic proximity effect. Using the anomalous Hall effect, the magnetization reversal of the system is observed by injecting a sufficiently large electrical current into the sample, under a constant external magnetic field that is applied parallel to the injected current. In addition, by conducting element-specific XMCD magnetization measurement, the switching of not the Co but the Pt magnetization is clearly detected. [ABSTRACT FROM AUTHOR]

We show that a CoFeB/MgO-based magnetic tunnel junction (MTJ) formed directly on a flexible substrate has considerable potential as a high-sensitivity strain gauge. A gauge factor of ∼1000, which represents the highest sensitivity reported, thus far, for a film-type strain gauge and is ∼500 times larger than that of the most prevalent metal-foil strain gauge, is realized in the flexible MTJ with a pseudo-spin valve structure under the condition of external magnetic-field assistance. Additionally, using a flexible MTJ with strain-insensitive exchange-biased pinned and strain-sensitive free layers, we demonstrate that a large resistance change due to the strain application can be achieved under magnetic field-free conditions. According to simulations based on the coherent magnetization rotation model, conditions are suggested for improving the gauge factor, as well as for using the flexible MTJ as a strain gauge in practical applications. [ABSTRACT FROM AUTHOR]

A tensile strain on the order of a few percent was created in Ni thin films deposited on a flexible polyethylene naphthalate substrate, and the strain-induced change in the magnetic anisotropy was investigated. The magnetic easy axis was reversibly switched by 90° by the application of the stress. The easy axis was orthogonal to the applied stress. The in-plane saturation magnetic field or the uniaxial magnetic anisotropy energy changed linearly in reaction to the applied tensile strain up to a strain of 2.3%. Moreover, a large difference in the saturation magnetic field up to ~0.3 T, which corresponds to a change in the magnetic anisotropy energy of ~7 × 104 J/m3, was realized. The effective magnetoelastic coupling constant was almost independent of the thickness of Ni. [ABSTRACT FROM AUTHOR]

This study investigates the electric-field effect on magnetic moments in perpendicularly magnetized Co ultra-thin films on a Pt underlayer. By applying electric fields to the Co surface through MgO/HfO2 insulating layers, we determined the change in the magnetic moment per one electrically increased electron. From systematic experiments at temperatures much below the Curie temperature, we found that the sign and the magnitude of the change depend on the nominal Co thickness tCo: the change nearly equals to −1 μB/electron for tCo ∼ 0.45 nm and more than +1 μB/electron at tCo ∼ 0.2 nm. The former value is consistent with the expectation from the celebrated Slater–Pauling curve. The latter value implies that one needs to consider some effects characteristic to Pt/Co system with extremely small tCo. The calculated band structures suggest that the intermixing between Co and Pt is related to the observed deviation from the Slater–Pauling curve with decreasing tCo. [ABSTRACT FROM AUTHOR]

We have demonstrated a reversible control of magnetic anisotropy in Pt/Co and Pd/Co structures formed on a polyethylene naphthalate flexible substrate by stretching the substrate biaxially. Compared with the case of the uniaxial tensile strain, which has been previously studied, the in-plane biaxial tensile strain produces much larger compressive strain normal to the plane, resulting in the significant modulation of the perpendicular magnetic anisotropy. We found the magnetic easy axis switching from in-plane to out-of-plane by applying up to 2% biaxial strain. In-plane magnetic anisotropy induced by the biaxial tensile strain is also investigated. [ABSTRACT FROM AUTHOR]

For the electric field-effect experiments that we present, the ferromagnetic semiconductor Mn-doped InAs [(In,Mn)As] (6) is incorporated as a channel layer in a metal-insulator-semiconductor field-effect transistor (FET) structure. In such [...], We report electrical manipulation of magnetization processes in a ferromagnetic semiconductor, in which low-density carriers are responsible for the ferromagnetic interaction. The coercive force [H.sub.c] at which magnetization reversal occurs can be manipulated by modifying the carrier density through application of electric fields in a gated structure. Electrically assisted magnetization reversal, as well as electrical demagnetization, has been demonstrated through the effect. This electrical manipulation offers a functionality not previously accessible in magnetic materials and may become useful for reversing magnetization of nanoscale bits for ultrahigh-density information storage.

In this report, current-induced spin–orbit torques (SOTs) in a permalloy (Py)/Pt/Co tri-layer system are investigated. In addition to the conventional SOTs generated from the spin Hall effect in the Pt layer, we observed a distinct existence of unconventional SOT acting on the in-plane magnetized Py layer in which the polarity of SOT reverses with the magnetization of perpendicularly magnetized Co. From its symmetry and experimental verifications, we conclude that this unconventional SOT, especially the damping-like torque term, originates from the additional spin current generated by the spin–orbit precession effect at the Pt/Co interface. Moreover, we reveal that the polarity of this SOT strongly depends on the interface structure of the ferromagnetic material/non-magnetic metal (NM), which can be controlled by the choice of NM material. The interface structure dependence shows a consistent result with first principle calculations of the spin–orbit precession effect that were previously reported. Our findings not only broaden the origin of the current-induced SOT but also pave the way for the design of high-efficient SOT-based devices. [ABSTRACT FROM AUTHOR]

The electric field (EF) modulation of magnetic domain wall (DW) creep velocity v in the Pt/Co/Pd structure with perpendicular magnetic anisotropy (MA) has been studied. The structures with different Co thicknesses tCo up to ∼1 nm are investigated. In all samples, applying a gate voltage induces a clear change in v. Thicker samples provide a higher v modulation efficiency, and the v modulation magnitude of more than a factor of 100 times is observed in the thickest tCo of 0.98 nm. The parameter characterizing the creep motion is significantly affected by the EF, resulting in the modulation of v. Unlike the v case, the MA modulation efficiency decreases with increasing tCo. The present results are discussed based on the EF-induced change in the interfacial Dzyaloshinskii–Moriya interaction (iDMI), which has been recently demonstrated in the same structure, and tCo dependence of the DW energy. The tCo dependence of the v modulation suggests that the EF effect on the iDMI is more important than the MA. [ABSTRACT FROM AUTHOR]

This study investigates the effect of high-temperature (350–500 °C) annealing on CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) directly formed on a flexible polyimide substrate, which has superior thermal tolerance. As the annealing temperature increases, the tunnel magnetoresistance (TMR) ratio enhances and reaches up to ∼200% at an annealing temperature of 450 °C. The annealing temperature dependence is similar to that of MTJs fabricated in the same way on a thermally oxidized silicon substrate. Images taken by a scanning transmission electron microscope confirm the improvement of the crystallization of the CoFeB and MgO layers, which can be an important factor in enhancing the TMR ratio. Furthermore, the endurance of the flexible MTJ against repeated stretching of its substrate is investigated. The TMR ratio shows no change during and after a 1000-cycle application of a tensile strain larger than 1%. The high TMR ratio and strain endurance demonstrated in this study suggest that the flexible MTJ structure is a promising candidate for a future strain-sensing device. [ABSTRACT FROM AUTHOR]

ac Susceptibility of a ferromagnetic semiconductor (Ga,Mn)As is measured by using microscaled Hall bar through the anomalous Hall effect. This method is used for detecting the change of the Curie temperature ([T.sub.C]) as a function of hole concentration by applying electric fields.

The field-effect transistor structures with a ferromagnetic [Ga.sub.1-x][Mn.sub.x]As channel having Mn composition of x = 0.027-0.200 are prepared. The studies have shown that the samples with larger x have higher Curie temperature [T.sub.C] and hole concentration p, while the controllable range of [T.sub.C] by applying external electric field has not increased with x.

The magnetic and the crystalline properties of a set of [Ga.sub.1-x][Mn.sub.x]As layers with high nominal Mn compositions (x=0.101-0.198) are examined. The studies have shown that the effective Mn composition has increased with the increase in the x value.

We report the relation between current induced effective fields and ferromagnetic layer thickness. Hall measurements with rotating magnetic field show that the transverse and perpendicular effective fields have linear relations to the inverse of the magnetic moment m per area S. The results imply that both of these effective fields may originate from spin angular momentum transferring. However, the non-zero intercept of the transverse field at m/S=0 implies that magnetization independent effects, such as Rashba effect, may contribute to transverse field. [ABSTRACT FROM AUTHOR]

The pulse-width and magnetic-field dependences of current-induced magnetization switching in a (Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is investigated. The magnetic-field dependence appears to indicate that the observed current-induced magnetization switching proceeds through metastable magnetization structures.

We have demonstrated that the strain direction can be detected sensitively using an exchange-biased spin valve (SV) formed on a flexible substrate. The flexible giant magnetoresistive SV used here contains a strain-sensitive Co free layer and a strain-insensitive exchange-biased NiFe pinned layer. The exchange bias is imparted from an antiferromagnetic FeMn layer stacked on the NiFe layer. When the strain is applied in a direction deviating from the exchange bias field, the free layer magnetization rotates along this directly only, resulting in a resistance change. Compared to the previously reported flexible pseudo SV, the present device allows strain direction sensing at a much smaller strain magnitude because no external magnetic field assistance is needed to fix the pinned layer magnetization, which hampers the rotation of the free layer magnetization. The robustness of the exchange bias to the strain in the simple NiFe/FeMn bilayer structure is also discussed. [ABSTRACT FROM AUTHOR]

The bit-to-bit distribution of a critical current density for magnetic domain wall (DW) motion is studied using Co/Ni wires with various wire widths (ws). The distribution inherently decreases with the w, and the ratio of standard deviation to average is 9.8% for wires with w=40 nm. It is found that a self-distribution within one device, which is evaluated through repeated measurement, is a dominant factor in the bit-to-bit distribution. Micromagnetic simulation reveals that the distribution originates from DW configuration, which varies with device size. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic and the crystalline properties of a set of Ga1-xMnxAs layers with high nominal Mn compositions (x=0.101–0.198). Magnetization measurements and combined channeling Rutherford backscattering (c-RBS) and particle induced x-ray emission (c-PIXE) measurements have been performed to determine the effective Mn composition xeff and the fraction of Mn atoms at various lattice sites. Here, xeff determined from magnetization measurements, which increases with increasing x, is consistent with the results determined from c-RBS-PIXE measurements. [ABSTRACT FROM AUTHOR]

The spin-dependent scattering in ferromagnet/nonmagnet/ferromagnet (Ga,Mn)As/(Al,Ga)As/(Ga,Mn)As trilayer structures was studied. An increase of sheet resistance was observed when the magnetizations of the two ferromagnetic (Ga,Mn)As layers were aligned anti-parallel, which was realized by the different coercivity of the two (Ga,Mn)As layers with different compositions. This is the first demonstration of spin-dependent scattering in magnetic multilayer structures made of semiconductor-materials alone. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We investigated the effect of surface oxidation of a ferromagnetic Co layer on current-induced spin-orbit torque. A Co thin film was deposited on a Pt underlayer, for which the spin current was expected to be generated through the spin Hall effect. Both the damping- and field-like torques quantitatively determined using harmonic Hall voltage measurements were clearly enhanced in the sample with the naturally oxidized Co layer. Even though the oxidized system possessed a larger perpendicular magnetic anisotropy and nearly the same areal magnetization value, i.e., the same effective ferromagnetic thickness, as those of the unoxidized sample, the electrical current required for magnetization switching was greatly reduced. The results clearly show that surface oxidization of a ferromagnetic thin film deposited on a heavy metal layer plays an important role in enlarging spin-orbit torque. [ABSTRACT FROM AUTHOR]

The perpendicular magnetic anisotropy (PMA) of a Co (0.5 nm)/Pt (2.4 nm) bilayer film was electrostatically tuned using a high-κ dielectric, SrTiO3, with a back-gating configuration. The Co film was directly deposited onto a SrTiO3 (001) substrate and capped by a Pt layer. The coercivity was enhanced (reduced) by applying a positive (negative) gate bias. The efficiency of the PMA energy modulation by the electric field was determined to be 1300-23 100 fJ/V m, which is 1-3 orders of magnitude higher than the efficiencies obtained in previous studies. The superior efficiency of this system is most likely attributable to the large dielectric constant of the SrTiO3 gate insulator and could be evidence that the PMA energy modulation is induced by charge accumulation. [ABSTRACT FROM AUTHOR]

The dielectric and magnetic properties of electric double layer (EDL) capacitor structures with a perpendicularly magnetized Pt/Co/Pt electrode and an insulating cap layer (MgO) are investigated. An electric field is applied through a mixed ionic liquid/ MgO barrier to the surface of the top Pt layer, at which the magnetic moment is induced by the ferromagnetic proximity effect. The basic dielectric properties of the EDL capacitor are studied by varying the thickness of the MgO cap layer. The results indicate that the capacitance, i.e., the accumulated charge density at the Pt surface, is reduced with increasing the MgO thickness. From the MgO thickness dependence of the capacitance value, the effective dielectric constant of the ionic liquid is evaluated. Almost no electric field effect on the magnetic moment, the coercivity, or the Curie temperature is confirmed in the top Pt layer with the thickness of 1.3 nm, regardless of the presence or absence of the MgO cap layer, whereas the a clear change in the magnetic moment is observed when the top Pt layer is replaced by a Pd layer of 1.7 nm. [ABSTRACT FROM AUTHOR]

We report on the temperature dependence of the magnetic anisotropy in Co/Pd/MgO system, in which magnetic moment in Pd is induced by the magnetic proximity effect. We demonstrate that the magnetic anisotropy is modulated by applying an electric field to the Pd surface. At temperatures below 100K, we find the nonlinear electric-field dependence of the anisotropy with the sign reversal. We obtain a huge anisotropy modulation efficiency of ∼1600 fJ/V m at 10K. [ABSTRACT FROM AUTHOR]

The electric field (EF) effect on the magnetic domain structure of a Pt/Co system was studied, where an EF was applied to the top surface of the Co layer. The width of the maze domain was significantly modified by the application of the EF at a temperature slightly below the Curie temperature. After a detailed analysis, a change in the microscopic exchange stiffness induced by the EF application was suggested to dominate the modulation of the domain width observed in the experiment. The accumulation of electrons at the surface of the Co layer resulted in an increase in the microscopic exchange stiffness and the Curie temperature. The result was consistent with the recent theoretical prediction. [ABSTRACT FROM AUTHOR]

We investigated the effect of electric current on the magnetic-field-driven magnetic domain wall (DW) creep velocity in ultrathin Co with perpendicular magnetic anisotropy deposited on a Pt underlayer. The DW velocity was considerably modulated by the current, and its field dependence deviated from the scaling law with the critical exponent of 1/4, which is generally valid in ferromagnetic metals. This characteristic feature of the DW motion can be explained by considering the perpendicular effective field generated by spin-orbit torque at the Pt/Co interface. From the relation between the injected current and the modified creep velocity, the determination of the effective field was demonstrated. [ABSTRACT FROM AUTHOR]

The Pt thickness dependence of the Curie temperature of perpendicularly magnetized ultra-thin (Pt/)Co/Pt films has been investigated by magnetization measurements. The Curie temperature and the saturation magnetic moment increase with the Co layer thickness and even with the Pt layer thickness. The Curie temperature is found to have linear dependence on the total magnetic moment of the system and the coefficients of the linear fits are almost identical, regardless of whether the thicknesses of the ferromagnetic Co layer or the Pt layer are varied. The Curie temperature also increases with the magnetic anisotropy, but no systematic dependence is observed. These results suggest that the magnetic moment induced in the Pt layer by the ferromagnetic proximity effect plays a significant role in determining the Curie temperatures of such twodimensional ferromagnetic systems. [ABSTRACT FROM AUTHOR]

We have produced stable organic field-effect transistors (OFETs) with an ultra-thin HfO2 gate insulator deposited directly on top of rubrene single crystals by atomic layer deposition (ALD). We find that ALD is a gentle deposition process to grow thin films without damaging rubrene single crystals, as results these devices have a negligibly small threshold voltage and are very stable against gate-bias-stress, and the mobility exceeds 1 cm2/V s. Moreover, the devices show very little degradation even when kept in air for more than 2 months. These results demonstrate thin HfO2 layers deposited by ALD to be well suited as high capacitance gate dielectrics in OFETs operating at small gate voltage. In addition, the dielectric layer acts as an effective passivation layer to protect the organic semiconductor. [ABSTRACT FROM AUTHOR]

Magnetization switching induced by electric fields in the absence of external magnetic field has been demonstrated in a field effect structure with a (Ga,Mn)As layer having an in-plane magnetic anisotropy. The switching is related to the modulation of the in-plane magnetic anisotropy by electric fields. Reducing magnetic anisotropy energy height by electric fields, we observe stochastic magnetization switching. [ABSTRACT FROM AUTHOR]

In this paper, we review the recent experimental developments on electric-field switching of ferromagnetism in ultra-thin Co films. The application of an electric field changes the electron density at the surface of the Co film, which results in modulation of its Curie temperature. A capacitor structure consisting of a gate electrode, a solid-state dielectric insulator and a Co bottom electrode is used to observe the effect. To obtain a larger change in the electron density, we also fabricated an electric double-layer capacitor structure using an ionic liquid. A large change in the Curie temperature of ~100K across room temperature is achieved with this structure. The application of the electric field influences not only the Curie temperature but also the domain-wall motion. A change in the velocity of a domain wall prepared in a Co micro-wire of more than one order of magnitude is observed. Possible mechanisms to explain the above-mentioned electric-field effects in Co ultra-thin films are discussed. (Some figures may appear in colour only in the online journal) [ABSTRACT FROM AUTHOR]

Controlling the position of a magnetic domain wall with electric current may allow for new types of non-volatile memory and logic devices. To be practical, however, the threshold current density necessary for domain wall motion must be reduced below present values. Intrinsic pinning due to magnetic anisotropy, as recently observed in perpendicularly magnetized Co/Ni nanowires, has been shown to give rise to an intrinsic current threshold Jth0. Here, we show that domain wall motion can be induced at current densities 40% below Jth0 when an external magnetic field of the order of the domain wall pinning field is applied. We observe that the velocity of the domain wall motion is the vector sum of current- and field-induced velocities, and that the domain wall can be driven against the direction of a magnetic field as large as 2,000 Oe, even at currents below Jth0. We show that this counterintuitive phenomenon is triggered by Walker breakdown, and that the additive velocities provide a unique way of simultaneously determining the spin polarization of current and the Gilbert damping constant. [ABSTRACT FROM AUTHOR]

Electrical control of magnetic properties is crucial for device applicationsin the field of spintronics. Although the magnetic coercivity or anisotropy has been successfully controlled electrically in metals as well as in semiconductors, the electrical control of Curie temperature has been realized only in semiconductors at low temperature. Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12?K by applying a gate electric field of about ±2?MV?cm?1. The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications. [ABSTRACT FROM AUTHOR]