Field-free magnetization reversal by spin Hall effect and exchange bias

Recently, is has been discovered that the magnetization of an ultra-thin out-of-plane ferromagnetic layer can be switched by the spin Hall effect (SHE). This spin Hall switching is a major contender for the write mechanism in novel magnetic memory devices such as MRAM (Magnetic Random Acces Memory). Unfortunately, an externally applied magnetic field is necessary to cause deterministic magnetization reversal by the SHE. Such a field is not suitable for implementation in actual devices.In this thesis, the external field is replaced by an effective magnetic field originating from the exchange bias effect between a ferromagnetic and an anti-ferromagnetic material. By creating an Pt/Co/IrMn trilayer in which the ferromagnetic Co layer is magnetized out-of-plane and the anti-ferromagnetic IrMn layer is magnetized in-plane, a novel exchange bias configuration, called orthogonal exchange bias, is successfully created. By investigating the thickness dependence of each layer, thermal stability and magnetic configurations, a thorough qualitative understanding of this system is achieved.By nanostructuring these orthogonal exchange biased samples, field-free deterministic magnetization reversal is observed via the SHE; a breakthrough in the field of MRAM research. The external field is successfully replaced by the intrinsic field from the exchange bias. The magnetization reversal showed characteristic features that appear to be intrinsic to the orthogonal exchange bias configuration. These features, most notably the gradual and partial switching of the magnetization, can be explained by the polycrystalline structure of the IrMn layer and current shunting related to the sample geometry. It is discovered that the effective exchange bias field can be compensated by applying a 5 mT external field. This compensation field is an order of magnitude smaller than the actual exchange bias that is found in full sheet samples. Whether this discrepancy is due to the nanostructuring of the sample or thermal effects on the exchange bias remains open for discussion. Still, this demonstration of field-free magnetization reversal by SHE and orthogonal exchange bias greatly increases the feasibility of future SHE-based MRAM devices. Recently, is has been discovered that the magnetization of an ultra-thin out-of-plane ferromagnetic layer can be switched by the spin Hall effect (SHE). This spin Hall switching is a major contender for the write mechanism in novel magnetic memory devices such as MRAM (Magnetic Random Acces Memory). Unfortunately, an externally applied magnetic field is necessary to cause deterministic magnetization reversal by the SHE. Such a field is not suitable for implementation in actual devices.In this thesis, the external field is replaced by an effective magnetic field originating from the exchange bias effect between a ferromagnetic and an anti-ferromagnetic material. By creating an Pt/Co/IrMn trilayer in which the ferromagnetic Co layer is magnetized out-of-plane and the anti-ferromagnetic IrMn layer is magnetized in-plane, a novel exchange bias configuration, called orthogonal exchange bias, is successfully created. By investigating the thickness dependence of each layer, thermal stability and magnetic configurations, a thorough qualitative understanding of this system is achieved.By nanostructuring these orthogonal exchange biased samples, field-free deterministic magnetization reversal is observed via the SHE; a breakthrough in the field of MRAM research. The external field is successfully replaced by the intrinsic field from the exchange bias. The magnetization reversal showed characteristic features that appear to be intrinsic to the orthogonal exchange bias configuration. These features, most notably the gradual and partial switching of the magnetization, can be explained by the polycrystalline structure of the IrMn layer and current shunting related to the sample geometry. It is discovered that the effective exchange bias field can be compensated by applying a 5 mT external field. This compensation field is an order of magnitude smaller than the actual exchange bias that is found in full sheet samples. Whether this discrepancy is due to the nanostructuring of the sample or thermal effects on the exchange bias remains open for discussion. Still, this demonstration of field-free magnetization reversal by SHE and orthogonal exchange bias greatly increases the feasibility of future SHE-based MRAM devices

Diversiteit op de Pabo

Aandacht voor diversiteit in teams van scholen en dus op de lerarenopleiding is een belangrijk speerpunt voor zowel de PO-raad (de raad waarin werkgevers in het primair onderwijs zich verenigd hebben) als de landelijke Vereniging Hogescholen in Nederland. Er worden drie groepen genoemd die in verband worden gebracht met een ervaren tekort aan diversiteit in onderwijsteams, namelijk een tekort aan mannelijke leraren, leraren met een niet-westers allochtone achtergrond en leraren die als voorafgaand aan de lerarenopleiding een middelbare beroepsopleiding hebben gevolgd (mbo). Dit zijn minderheidsgroepen binnen teams in basisscholen, maar ook binnen de studentenpopulatie op de lerarenopleiding. Bij deze studenten is de instroom relatief laag, de doorstroom moeizamer en vaker dan gemiddeld vallen zij uit zonder diploma. Het voorliggend onderzoek wil meer helderheid verschaffen over voor de opleiding relevante verschillen tussen de doorsnee pabostudent en studenten uit de minderheidsgroepen. Er is gezocht naar kenmerken en factoren waarop studenten kunnen worden onderscheiden en die relevant zijn voor hun professionele identiteit. Door middel van een vragenlijst is geprobeerd een beschrijving te geven van de studentenpopulatie van de pedagogische academie voor basisonderwijs (pabo) in Nederland. In totaal hebben 551 studenten van één opleiding - de HAN Pabo - de vragenlijst volledig ingevuld. De genoemde minderheidsgroepen verschillen op een aantal onderdelen significant van elkaar en van de meerderheidsgroep. Met deze vragenlijst is de diversiteit van de HAN Pabo beter in kaart gebracht; gegevens die de opleiding kan gebruiken om het opleidingsprogramma meer op maat van de diverse studenten te maken

Field-free magnetization reversal by spin-Hall effect and exchange bias

International audienceAs the first magnetic random access memories are finding their way onto the market, an important issue remains to be solved: the current density required to write magnetic bits becomes prohibitively high as bit dimensions are reduced. Recently, spin–orbit torques and the spin-Hall effect in particular have attracted significant interest, as they enable magnetization reversal without high current densities running through the tunnel barrier. For perpendicularly magnetized layers, however, the technological implementation of the spin-Hall effect is hampered by the necessity of an in-plane magnetic field for deterministic switching. Here we interface a thin ferromagnetic layer with an anti-ferromagnetic material. An in-plane exchange bias is created and shown to enable field-free S HE-driven magnetization reversal of a perpendicularly magnetized Pt/Co/IrMn structure. Aside from the potential technological implications, our experiment provides additional insight into the local spin structure at the ferromagnetic/anti-ferromagnetic interface

Field-free magnetization reversal by spin-Hall effect and exchange bias

As the first magnetic random access memories are finding their way onto the market, an important issue remains to be solved: the current density required to write magnetic bits becomes prohibitively high as bit dimensions are reduced. Recently, spin–orbit torques and the spin-Hall effect in particular have attracted significant interest, as they enable magnetization reversal without high current densities running through the tunnel barrier. For perpendicularly magnetized layers, however, the technological implementation of the spin-Hall effect is hampered by the necessity of an in-plane magnetic field for deterministic switching. Here we interface a thin ferromagnetic layer with an anti-ferromagnetic material. An in-plane exchange bias is created and shown to enable field-free S HE-driven magnetization reversal of a perpendicularly magnetized Pt/Co/IrMn structure. Aside from the potential technological implications, our experiment provides additional insight into the local spin structure at the ferromagnetic/anti-ferromagnetic interface\u3cbr/\u3