Search

We propose a magnetic random access memory (MRAM) cell that utilizes field-induced switching and is applicable to high-speed memories. The MRAM cell, called the shape-varying MRAM cell, has three free layers, each having different shapes and functions, and achieves low write-current switching with high thermal stability and high external field robustness. We show analytically that one of the layers contributes to the low write-current switching and another contributes to the thermal stability. We also show the results of a micromagnetic simulation, in which write current of <0.5 mA, write time of <2 ns, energy barrier (ΔE/kBT)>100, and external field robustness of >32 Oe were obtained. [ABSTRACT FROM AUTHOR]

Current-driven domain wall motion from pinning sites in nanostrips with perpendicular magnetic anisotropy is studied by using micromagnetic simulations, supported by a one-dimensional model of wall dynamics. The threshold current density of perpendicular anisotropy strips is much smaller than that of in-plane anisotropy strips, and is almost independent of the pinning potential strength. This results from the narrower domain wall width, smaller hard-axis anisotropy, and the larger ratio of the depinning field and hard-axis anisotropy. In the one-dimensional model with a zero damping constant, the threshold current density is found to be about 0.72 of the intrinsic threshold current density for a perfect strip in a strong pinning regime that corresponds to strips with perpendicular magnetic anisotropy. The fact that the threshold current density from the pinning sites is smaller than the intrinsic current density is because the effective field, equivalent to the pinning potential, enhances a breakdown in the pinning site. Moreover, in the strong pinning regime, an opposite-direction depinning hardly ever occurs after current pulse is turned off. These features of strips with perpendicular magnetic anisotropy are attractive for magnetic random access memories where the domain wall should be moved stably between the pinning sites with the small current pulse. [ABSTRACT FROM AUTHOR]

We calculate writing characteristics of two kinds of low-current magnetic random access memory (MRAM) devices using a single domain model. A four-layer synthetic antiferromagnet (SAF) has four antiferromagnetically coupled ferromagnetic (FM) layers, and a two-SM-layer-FC SAF has a two-FM-layer SAF with ferromagnetically coupled (FC) two soft magnetic (SM) layers. The threshold field of these free layers can be calculated analytically. The spin flop field of four-FM-layer SAF film is independent of the strength of antiferromagnetic coupling (AFC) between inner films. The saturation field increases with increasing the AFC strength. The spin flop field of the two-SM-layer-FC SAF film decreases, and the saturation field increases with decreasing ferromagnetic coupling strength. However, activation energy analysis demonstrates that both types of films exhibit a decrease in activation energy near the spin flop field. Considering the activation energy decrease during the toggling write sequence and a sufficient writing margin, MRAM with four ferromagnetic layers decreases writing current by 40%. [ABSTRACT FROM AUTHOR]

Laminated hard disk heads with FeTaN films, which have high saturation magnetic flux density of 16KG, have been newly developed for high density magnetic recording. In this study, read/write characteristics for FeTaN heads were evaluated and compared with the value for Sendust laminated heads. The FeTaN heads have better overwrite characteristics by 10dB than Sendust heads. Even for 2400 Oe high coercivity media, the overwrite value is -32dB. Output voltage for the FeTaN head is at least 1.2times higher than that for a Sendust head. Popcorn noise and wiggle noise are low enough for practical use. FeTaN heads are shown to have a great potential to achieve high a real density recording.

A shape-varying magnetic tunneling junction (MTJ) (SVM) is developed that has a high MR ratio and low write current for use in high-speed magnetic random access memory (MRAM) cells. The switching magnetic field of synthetic ferromagnetic coupling free layer (SFF) is reduced with the increase in the thickness of NiFe.

A write-line-inserted magnetic tunneling junction (MTJ) (WLIM) is developed for using in low-write-current magnetoresistance random access memory (MRAM). A high write-current magnetic-field efficiency is obtained when the aspect ratio of the MTJs is low, indicating that WLIM structure has advantages for using in low-write-current MRAM.

Current driven domain wall motion in nanostrips with perpendicular magnetic anisotropy is analyzed by using micromagentic simulation. The calculations have shown that the threshold current density of perpendicular magnetic anisotropy (PMA) strips required to depin the domain wall is small although the threshold field is sufficiently large relative to those of in-plane magnetic anisotropy (IMA) strips.

The critical current density needed for the current-induced domain wall motion ([J.sub.c]) is reduced by decreasing the magnetization ([M.sub.s]) of the free layer film of a U-shaped pattern for a domain wall motion memory. It is shown that the decrease in [M.sub.s] has caused a decrease in the hard axis anisotropy of the pattern and the [J.sub.c] has decreased, which is predicted by a one-dimensional model.

The magnetoresistance ratio (MR) and resistance area product (RA) of cap/NiFe/Al[O.sub.x] /CoFe stack with several cap layers are investigated and a model explaining correlation between MR ratio and RA and the cap layer material is proposed, in a viewpoint of the standard electrode potential. The highest MR ratio with nonmagnetic-NiFeZr cap is consistent with the lowest electrode potential of Zr, and it is believed that non-magnetic-NiFeZr cap realizes a steep NiFe/AlOx interface without the oxidation of NiFe.

The magnetoresistive tunneling junctions (MTJ) edge oxidation effect on the switching field distribution (SFD) is investigated and the magnetic switching process is analyzed by utilizing the micro magnetic modeling simulation for 0.24 X 0.48 [mu][m.sub.2] MTJs. The results of the simulation predict that the edge magnetization reversals are suppressed by the MTJ edge [M.sub.s] reduction and the edge domain size at the remanent states becomes small.

A write-operating window with a 100% functional bit yield is obtained by the control of stray fields from synthetic antiferromagnetic (SAF) pinned layers in conventional magnetic random access memories. The symmetric switching astroid curves with no offset are obtained and the switching distributions are minimized at the zero offset field.

We have developed a Co-Ni-Fe write head with a short yoke length for high-speed recording. By reducing the yoke length to 9.5 [micro]m, the eddy currents induced in a yoke with a relatively low resistivity (0.2 [micro][Omega]m) were reduced. The head of this short yoke had good write performance for a medium with a coercivity of 400 kA/m (5000 Oe) at frequencies up to 250 MHz (the overwrite less than - 30 dB, and nonlinear transition shift less than 7%). Index Terms--Eddy currents, high-Bs material, high-speed recording, short yoke length, write head.

The relationship between the effects of isoflavone supplementation on bone mineral density and climacteric symptoms and equol-producing ability was assessed by using a randomized trial of soy isoflavone treatment in Japanese women. A double-blind placebo-controlled crossover trial with an isoflavone supplement (IF) of 40 mg/d was carried out in 42 climacteric Japanese women. A questionnaire and an interview covered climacteric symptoms, health status, dietary and exercise habits, and medical history. The following measurements were made at baseline and after 4 and 8 wk of treatment: anthropometrical measurements, blood pressure, bone mineral density (BMD), blood status, and plasma biochemicals. Urinary isoflavones and metabolites were separately measured from refrigerated samples. The number of equol producers both at baseline and after IF treatment (P-P) was 17 (40.5%), of nonproducers at both periods (N-N) was 12 (28.6%), of producers at baseline who changed to producers after IF (P-N) was 7 (16.7%), and of nonproducers at baseline who became producers after IF (N-P) was 6 (14.3%). Urinary equol concentration was higher after IF treatment than after placebo treatment (P = 0.06). There was no significant difference in the average age of each group. The menopausal index score in the P-P group was lower (18 points) than in the other groups (26-31 points). The equol nonproducers at both baseline and after IF treatment had high body fat (30.1%) and high systolic blood pressure (148 mm Hg), and their BMD and climacteric symptoms did not improve with IF treatment. Women who became equol producers after IF treatment (N-P) showed lower plasma LDL at baseline (3.34 vs. 3.39-4.01 mmol/L) and greater improvement in BMD and climacteric symptoms ([+ or -] 0.14 g/[cm.sup.3], -5 points) compared with the other groups. Baseline anthropometric and cholesterol levels and effects of IF treatment on cholesterol, BMD, and climacteric symptoms differed according to equol-producing ability.

Premenstrual syndrome (PMS) is characterized by psychological and/or physical symptoms during the luteal phase of the menstrual cycle. PMS affects a large segment of the population of reproductive-age women. We studied the effects of 2 isoflavone (IF) supplements on the improvement of PMS symptoms. A total of 242 women, aged 18-21 y, voluntarily participated in a questionnaire study on PMS. Premenstrual symptoms interfering with daily life activity were reported by 86.0% of all subjects. Major symptoms were sleepiness, abdominal pain, backache, headache, breast tenderness, and mental irritability. The severity of PMS was related to menstrual pain and to previous dieting for weight loss. From the questionnaire study, 56 women with PMS were selected to participate in a randomized double-blind crossover intervention trial with IFs and placebo. In the supplement groups, 26 (20 mg/d of IFs) and 28 (40 mg/d of IFs) women completed the study that lasted for 8 menstrual cycles, with 3 menstrual cycles of baseline assessment and 2 menstrual cycles of IF or placebo tablet administration. No significant differences in physical and nutritional characteristics between the groups receiving IFs at 20 and 40 mg/d were observed at entry into the intervention trial. Average IF intake from the diet was 20.7 mg/d. The ratio of estradiol to progesterone at the luteal phase tended to decrease with IF treatment in the subjects with severe PMS. Physical symptoms (particularly headache) were significantly improved in the group receiving 40 mg/d compared with placebo group (P < 0.05); in this IF group, increased plasma serotonin concentration (possibly related to decrease in headaches) was observed. Psychological symptoms did not show significant improvement. Individual personality assessed by the NEO Personality Inventory was related to the severity of PMS. Significant associations between openness and mental irritability, agreeableness and acne and mental symptoms, and conscientiousness and headache were present (P < 0.05). We suggest that an IF supplement may be an effective treatment for the improvement of physical PMS symptoms.