Multiple-stable anisotropic magnetoresistance memory in antiferromagnetic MnTe

Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic materials. Recently, experimental bistable memories have been realized using fully compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II–VI semiconductors. Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Neel vector aligned along one of the three magnetic easy axes. The robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states are unique properties of antiferromagnets

Interdiffusion in EuS -based epitaxial superlattice nanostructures

The diffusion intermixing of layers during annealing of EuS -based epitaxial superlattice nanostructures was studied by X-ray diffraction technique. The interdiffusion coefficients for EuS —PbS , EuS —PbSe , EuS —SrS superlattices were determined basing on change of the intensity of near-Bragg reflection satellites in X-ray diffraction pattern. There are no layer intermixing in EuS —PbTe superlattice was observed

Investigation of the growth mechanism, structure, and thermoelectric properties of thin PbTe films grown on mica

The growth mechanisms, structure and thermoelectric properties of thin PbTe films prepared by thermal evaporation in vacuum and subsequent deposition on mica substrates at temperatures Ts = 375, 525 and 635 К were studied. The films were prepared from charge with different electron concentrations (n = 10¹⁷ and n = 10²⁰ cm⁻³). The film thickness was varied in the range d =4-500 nm. Electron microscopy study showed that PbTe grows on mica epitaxially in an island like fashion predominantly in the (111) orientation. It is established that in PbTe films there exists a critical thickness at which the transition from electron to hole conductivity with decreasing d is observed. Covering films with a protective layer, lowering the substrate temperature and increasing electron concentration in the charge result in narrowing of the thickness range corresponding to hole conductivity. It is shown that electron concentrations n in the charge and in thick PbTe films grown at the substrate temperature Ts = 525 К differ, the character and magnitude of this difference depending on n in the charge.Исследованы механизм роста, структура и термоэлектрические свойства тонких пленок РЬТе, полученных термическим испарением в вакууме на подложки из слюды. Варьировались толщина пленок (d = 4-500 нм), температура подложки (Т3 = 375, 525 и 635 К) и концентрация носителей заряда в исходной шихте (п = 10¹⁷ и п = 10²⁰ см⁻³). Методом электронной микроскопии установлено, что РbТе растет на слюде эпитаксиально по островковому механизму преимущественно в ориентации (111). Установлено, что в пленках РbТе существует критическая толщина, при которой наблюдается переход от электронной к дырочной проводимости при уменьшении d. Нанесение на пленки защитного покрытия, снижение температуры подложки и увеличение концентрации электронов в шихте приводят к сужению интервала толщин, соответствующих дырочной проводимости. Показано, что значения концентрации электронов п в шихте и толстых пленках РbТе, полученных при температуре подложки Ts = 525К, различаются, причем характер и величина этого изменения зависят от n в шихте.Досліджено механізм росту, структура і термоелектричні властивості тонких плівок РbТе, одержаних термічним випаровуванням у вакуумі на підкладки із слюди. Варіювались товщина плівок (d = 4-500 нм), температура підкладки (Т3 = 375, 525 и 635 К) та концентрація носіїв заряду у вихідній шихті (п = 10¹⁷ и п = 10²⁰ см⁻³). Методом електронної мікроскопії встановлено, що РbТе росте на слюді епітаксіально за острівковим механізмом переважно в орієнтації (111). Встановлено, що у плівках РЬТе існує критична товщина, при якій спостерігається перехід від електронної до діркової провідності при зменшенні d. Нанесення на плівки захисного покриття, зниження температури підкладки та збільшення концентрації електронів у шихті приводять до зменшення інтервалу товщин, який відповідає дірковій провідності. Показано, що значення концентрації електронів n у шихті і товстих плінках РЬТе, одержаних при температурі підкладки Ts = 525 К, відрізняються, а характер і величина цієї відмінності залежать від n у шихті

Pt/Co (4)/NiO thin film perpendicular magnetic anisotropy dependence on Co layer thickness

We have examined the dependence of the magnetism from perpendicular magnetic anisotropy with Co thickness in [Pt/Co] multilayers coupled to a NiO layer. We measure a perpendicular exchange bias field that changes polarity with Co thickness and find that with 2 nm of Co the perpendicular magnetic anisotropy is no longer present. Further evidence of the change in the Co layers preferred orientation is offered by zero field cooled susceptometry, where the low temperature susceptibility is negative for thin Co layers (0.9-1.2 nm) and becomes positive with increasing Co thickness (1.5-2.0 nm). Thin Co layered films also exhibit a compensation point around 100 K. These results indicate that the Co and NiO interface moments are coupled strongly and that there is competition between Pt/Co and Co/Ni at the film layer interfaces that sets the overall anisotropy from perpendicular and parallel configurations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3340511

Magnetization study of interlayer exchange in semiconductor EuS-PbS ferromagnetic wedge multilayers

Interlayer coupling was exptl. studied in semiconductor EuS-PbS ferromagnetic superlattice wedge structures grown on KCl (0 0 1) substrates with the wedges covering the semiconductor nonmagnetic PbS spacer layer thickness from 0.3 to 6 nm. Structural parameters of the wedges were examd. by X-ray diffraction anal. of EuS-PbS superlattice period. Measurements of magnetic hysteresis loops of EuS-PbS structures were performed by both SQUID (for small terminal parts of the wedge) and MOKE (magneto-optical anal. along the wedge) magnetometry. A strong decrease of magnetic remanence and an increase of satn. field obsd. for EuS-PbS structures with the PbS spacer thickness decreasing below about 1.5 nm is discussed in terms of the influence of antiferromagnetic interlayer coupling

Magnetization of EuS-PbS multilayers with antiferromagnetic interlayer coupling

SQUID magnetometry is applied to study the temperature and magnetic field dependence of magnetization M(T, H) of semiconductor EuS–PbS ferromagnetic multilayers grown on insulating KCl(100) and conducting n-PbS(100) monocrystalline substrates. For low external magnetic fields (of the order of 10 Oe) and PbS spacer layers thinner than about 2 nm, we observe in EuS–PbS–EuS trilayers the strongly nonmonotonic temperature dependence of magnetization with almost zero total magnetic moment below the Curie temperature. The application of the magnetic field of the order of 100 Oe restores the regular monotonic increase of magnetization with decreasing temperature. To explain this M(T,H) dependence we present a model that considers the competition of three (temperature dependent) contributions to the total magnetic energy of the trilayer: the antiferromagnetic interlayer interaction energy, the Zeeman energy, and the energy of in-plane magnetocrystalline anisotropy